text: PSD Publications: No conditions. Results ordered Authors, Title. 2017-07-28T09:52:56Z EPrints http://www.esrl.noaa.gov/images/banner_psd.png http://www.esrl.noaa.gov/psd/pubs/ 2012-11-15T19:37:32Z 2013-02-08T23:11:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/801 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/801 2012-11-15T19:37:32Z Climate Dynamics: Why does Climate Vary? Climate Dynamics: Why Does Climate Vary? presents the major climate phenomena within the climate system to underscore the potency of dynamics in giving rise to climate change and variability. These phenomena include deep convection over the Indo-Pacific warm pool and its planetary-scale organization: the Madden-Julian Oscillation, the monsoons, the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, and the low-frequency variability of extratropical circulations. The volume also has a chapter focusing on the discussion of the causes of the recent melting of Arctic sea ice and a chapter devoted to the discussion of the causes of recent changes in the frequency and intensity of tropical cyclones. On each topic, the basic material of climate dynamics is covered to aid the understanding of the forefront research, making the volume accessible to a broad spectrum of readers. 2012-11-09T20:22:29Z 2013-02-05T21:37:40Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/586 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/586 2012-11-09T20:22:29Z Climate Variability and Extremes during the Past 100 years N/A make_name_string expected hash reference make_name_string expected hash reference make_name_string expected hash reference make_name_string expected hash reference make_name_string expected hash reference 2012-11-13T20:09:16Z 2013-02-11T23:26:06Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/641 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/641 2012-11-13T20:09:16Z Dendroclimatology: Progress and Prospects N/A 2015-11-19T23:22:10Z 2016-04-12T16:32:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1293 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1293 2015-11-19T23:22:10Z Explaining Extreme Events of 2014 from a Climate Perspective N/A 2017-07-07T20:44:55Z 2017-07-07T20:44:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1516 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1516 2017-07-07T20:44:55Z Optimizing observations of drizzle onset with millimeter-wavelength radars Cloud Doppler radars are increasingly used to study cloud and precipitation microphysical processes. Typical bulk cloud properties such as liquid or ice content are usually derived using the first three standard moments of the radar Doppler spectrum. Recent studies demonstrated the value of higher moments for the reduction of retrieval uncertainties and for providing additional insights into microphysical processes. Large effort has been undertaken, e.g., within the Atmospheric Radiation Measurement (ARM) program to ensure high quality of radar Doppler spectra. However, a systematic approach concerning the accuracy of higher moment estimates and sensitivity to basic radar system settings, such as spectral resolution, integration time and beam width, are still missing. In this study, we present an approach on how to optimize radar settings for radar Doppler spectra moments in the specific context of drizzle detection. The process of drizzle development has shown to be particularly sensitive to higher radar moments such as skewness. We collected radar raw data (I/Q time series) from consecutive zenith-pointing observations for two liquid cloud cases observed at the cloud observatory JOYCE in Germany. The I/Q data allowed us to process Doppler spectra and derive their moments using different spectral resolutions and integration times during identical time intervals. This enabled us to study the sensitivity of the spatiotemporal structure of the derived moments to the different radar settings. The observed signatures were further investigated using a radar Doppler forward model which allowed us to compare observed and simulated sensitivities and also to study the impact of additional hardware-dependent parameters such as antenna beam width. For the observed cloud with drizzle onset we found that longer integration times mainly modify spectral width (Sw) and skewness (Sk), leaving other moments mostly unaffected. An integration time of 2 s seems to be an optimal compromise: both observations and simulations revealed that a 10 s integration time – as it is widely used for European cloud radars – leads to a significant turbulence-induced increase of Sw and reduction of Sk compared to 2 s integration time. This can lead to significantly different microphysical interpretations with respect to drizzle water content and effective radius. A change from 2 s to even shorter integration times (0. 4 s) has much smaller effects on Sw and Sk. We also find that spectral resolution has a small impact on the moment estimations, and thus on the microphysical interpretation of the drizzle signal. Even the coarsest spectral resolution studied, 0. 08 ms−1, seems to be appropriate for calculation moments of drizzling clouds. Moreover, simulations provided additional insight into the microphysical interpretation of the skewness signatures observed: in low (high)-turbulence conditions, only drizzle larger than 20 µm (40 µm) can generate Sk values above the Sk noise level (in our case 0.4). Higher Sk values are also obtained in simulations when smaller beam widths are adopted. C. Acquistapace S. Kneifel P. Löhnert P. Kollias M. Maahn M. Bauer-Pfundstein 2015-10-07T14:34:01Z 2015-10-07T14:34:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1217 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1217 2015-10-07T14:34:01Z Water and climate: Recognize anthropogenic drought N/A A. AghaKouchak D. Feldman M. P. Hoerling T. Huxman J. Lund 2015-04-24T17:07:03Z 2015-04-29T14:47:49Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1143 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1143 2015-04-24T17:07:03Z Understanding high wintertime ozone pollution events in an oil- and natural gas-producing region of the western US Recent increases in oil and natural gas (NG) production throughout the western US have come with scientific and public interest in emission rates, air quality and climate impacts related to this industry. This study uses a regional-scale air quality model (WRF-Chem) to simulate high ozone (O3) episodes during the winter of 2013 over the Uinta Basin (UB) in northeastern Utah, which is densely populated by thousands of oil and NG wells. The high-resolution meteorological simulations are able qualitatively to reproduce the wintertime cold pool conditions that occurred in 2013, allowing the model to reproduce the observed multi-day buildup of atmospheric pollutants and the accompanying rapid photochemical ozone formation in the UB. Two different emission scenarios for the oil and NG sector were employed in this study. The first emission scenario (bottom-up) was based on the US Environmental Protection Agency (EPA) National Emission Inventory (NEI) (2011, version 1) for the oil and NG sector for the UB. The second emission scenario (top-down) was based on estimates of methane (CH4) emissions derived from in situ aircraft measurements and a regression analysis for multiple species relative to CH4 concentration measurements in the UB. Evaluation of the model results shows greater underestimates of CH4 and other volatile organic compounds (VOCs) in the simulation with the NEI-2011 inventory than in the case when the top-down emission scenario was used. Unlike VOCs, the NEI-2011 inventory significantly overestimates the emissions of nitrogen oxides (NOx), while the top-down emission scenario results in a moderate negative bias. The model simulation using the top-down emission case captures the buildup and afternoon peaks observed during high O3 episodes. In contrast, the simulation using the bottom-up inventory is not able to reproduce any of the observed high O3 concentrations in the UB. Simple emission reduction scenarios show that O3 production is VOC sensitive and NOx insensitive within the UB. The model results show a disproportionate contribution of aromatic VOCs to O3 formation relative to all other VOC emissions. The model analysis reveals that the major factors driving high wintertime O3 in the UB are shallow boundary layers with light winds, high emissions of VOCs from oil and NG operations compared to NOx emissions, enhancement of photolysis fluxes and reduction of O3 loss from deposition due to snow cover. R. Ahmadov . . . R. J. Zamora 2013-08-13T17:25:15Z 2013-08-13T17:25:15Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/935 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/935 2013-08-13T17:25:15Z Continental-scale temperature variability during the past two millennia Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between AD 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period AD 1971–2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years. M. Ahmed K. J. Anchukaitis Asrat Asfawossen . . . H. F. Diaz 2016-04-11T20:12:14Z 2016-06-13T21:35:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1307 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1307 2016-04-11T20:12:14Z Tropical Upper Tropospheric Potential Vorticity Intrusions During Sudden Stratospheric Warmings We examine the intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings (SSWs). Our analysis reveals that SSW-related PV intrusions are significantly stronger, penetrate more deeply into the tropics, and exhibit distinct geographic distributions compared to their climatological counterparts. While climatological upper tropospheric and lower stratospheric (UTLS) PV intrusions are generally attributed to synoptic scale Rossby wave breaking, we find that SSW-related PV intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional PV gradient maximum equatorward. As these deformations unfold, planetary-scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical UTLS. In addition, the material PV deformations also reorganize the geographic structure of the UTLS waveguide, which alters where synoptic scale waves break. In combination, these two intrusion mechanisms provide a robust explanation describing why displacement and split SSWs – or more generally, anomalous stratospheric planetary wave events – produce intrusions with unique geographic distributions: displacement SSWs have a single PV intrusion maximum over the Pacific Ocean, while split SSWs have intrusion maxima over the Pacific and Indian Oceans. We also show that the two intrusion mechanisms involve distinct timescales of variability and highlight that they represent an instantaneous and direct link between the stratosphere and troposphere. This is in contrast to higher latitude stratosphere-troposphere coupling that occurs indirectly via wave-mean flow feedbacks. J. R. Albers G. N. Kiladis T. Birner J. Dias 2013-01-17T16:39:55Z 2013-05-07T20:01:57Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/876 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/876 2013-01-17T16:39:55Z Extratropical air-sea interaction, sea surface temperature variability, and the Pacific Decadal Oscillation We examine processes that influence North Pacific sea surface temperature (SST) anomalies including surface heat fluxes, upper ocean mixing, thermocline variability, ocean currents, and tropical-extratropical interactions via the atmosphere and ocean. The ocean integrates rapidly varying atmospheric heat flux and wind forcing, and thus a stochastic model of the climate system, where white noise forcing produces a red spectrum, appears to provide a baseline for SST variability even on decadal time scales. However, additional processes influence Pacific climate variability including the "reemergence mechanism," where seasonal variability in mixed layer depth allows surface temperature anomalies to be stored at depth during summer and return to the surface in the following winter. Wind stress curl anomalies in the central/east Pacific drive thermocline variability that propagates to the west Pacific via baroclinic Rossby waves and influences SST by vertical mixing and the change in strength and position of the ocean gyres. Atmospheric changes associated with the El Niño-Southern Oscillation (ENSO) also influence North Pacific SST anomalies via the "atmospheric bridge." The dominant pattern of North Pacific SST anomalies, the Pacific Decadal Oscillation (PDO), exhibits variability on interannual as well as decadal time scales. Unlike ENSO, the PDO does not appear to be a mode of the climate system, but rather it results from several different mechanisms including (1) stochastic heat flux forcing associated with random fluctuations in the Aleutian Low, (2) the atmospheric bridge augmented by the reemergence mechanism, and (3) wind-driven changes in the North Pacific gyres. M. A. Alexander 2012-11-09T16:55:37Z 2013-05-08T15:35:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/574 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/574 2012-11-09T16:55:37Z Decadal variability in the northeast Pacific in a physical-ecosystem model: Role of mixed layer depth and trophic interactions A basin-wide interdecadal change in both the physical state and the ecology of the North Pacific occurred near the end of 1976. Here we use a physical-ecosystem model to examine whether changes in the physical environment associated with the 1976–1977 transition influenced the lower trophic levels of the food web and if so by what means. The physical component is an ocean general circulation model, while the biological component contains 10 compartments: two phytoplankton, two zooplankton, two detritus pools, nitrate, ammonium, silicate, and carbon dioxide. The model is forced with observed atmospheric fields during 1960–1999. During spring, there is a ∼40% reduction in plankton biomass in all four plankton groups during 1977–1988 relative to 1970–1976 in the central Gulf of Alaska (GOA). The epoch difference in plankton appears to be controlled by the mixed layer depth. Enhanced Ekman pumping after 1976 caused the halocline to shoal, and thus the mixed layer depth, which extends to the top of the halocline in late winter, did not penetrate as deep in the central GOA. As a result, more phytoplankton remained in the euphotic zone, and phytoplankton biomass began to increase earlier in the year after the 1976 transition. Zooplankton biomass also increased, but then grazing pressure led to a strong decrease in phytoplankton by April followed by a drop in zooplankton by May: Essentially, the mean seasonal cycle of plankton biomass was shifted earlier in the year. As the seasonal cycle progressed, the difference in plankton concentrations between epochs reversed sign again, leading to slightly greater zooplankton biomass during summer in the later epoch. M. A. Alexander A. Capotondi A. Miller et al. 2015-04-20T19:06:03Z 2015-04-29T14:11:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1120 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1120 2015-04-20T19:06:03Z Climate variability during warm and cold phases of the Atlantic Multidecadal Oscillation (AMO) 1871–2008. An extended reanalysis, a combination of observations and model output, is used to examine the spatial patterns of physical variables associated with the Atlantic Multidecadal Oscillation (AMO) from 1871 to 2008. The results are presented as anomalies during positive and negative phases of the AMO. As in previous studies, during positive (negative) AMO phases the sea surface temperature (SST) is anomalously warm (cold) over most of the North Atlantic, with the exception of the east coast of the United States. The atmospheric patterns, associated with the positive phase of the AMO, include anomalous low pressure over the Atlantic between 20°S and 50°N, cyclonic surface winds around the low, reduced wind speeds over the tropical Atlantic and enhanced precipitation in the eastern tropical Atlantic, with roughly opposite conditions during negative AMO phases. There are, however, substantial differences in the SST and the atmospheric anomalies between periods of the same phase, especially in the extratropics. Correlations between the AMO and air temperature anomalies are positive over much of the globe between 40°S and 50°N, with correlations exceeding 0.6 (~ 95% significance level) over the Maritime Continent and northern rim of the Pacific Ocean. Most of the sea level pressure (SLP) anomalies beyond the Atlantic are not statistically significant. M. A. Alexander K. H. Kilbourne J. A. Nye 2012-11-09T17:33:00Z 2013-05-08T15:36:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/575 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/575 2012-11-09T17:33:00Z Forecasting Pacific SSTs: Linear Inverse Model Predictions of the PDO A linear inverse model (LIM) is used to predict Pacific (30°S–60°N) sea surface temperature anomalies (SSTAs), including the Pacific decadal oscillation (PDO). The LIM is derived from the observed simultaneous and lagged covariance statistics of 3-month running mean Pacific SSTA for the years 1951–2000. The model forecasts exhibit significant skill over much of the Pacific for two to three seasons in advance and up to a year in some locations, particulary for forecasts initialized in winter. The predicted and observed PDO are significantly correlated at leads of up to four seasons, for example, the correlation exceeds 0.6 for 12-month forecasts initialized in January–March (JFM). The LIM-based PDO forecasts are more skillful than persistence or a first-order autoregressive model, and have comparable skill to LIM forecasts of El Niño SSTAs. Filtering the data indicates that much of the PDO forecast skill is due to ENSO teleconnections and the global trend. Within LIM, SST anomalies can grow due to constructive interference of the empirically determined modes, even though the individual modes are damped over time. For the Pacific domain, the basinwide SST variance can grow for 14 months, consistent with the skill of the actual predictions. The optimal structure (OS), the initial SSTA pattern that LIM indicates should increase the most rapidly with time, is clearly relevant to the predictions, as the OS develops into a mature ENSO and PDO event 6–10 months later. The OS is also consistent with the seasonal footprinting mechanism (SFM) and the meridional mode (MM); the SFM and MM involve a set of atmosphere–ocean interactions that have been hypothesized to initiate ENSO events. M. A. Alexander L. Matrosova C. Penland J. D. Scott P. Chang 2012-11-09T17:34:35Z 2013-05-08T15:38:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/576 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/576 2012-11-09T17:34:35Z The Role of Ekman Ocean Heat Transport in the Northern Hemisphere Response to ENSO The influence of oceanic Ekman heat transport (Qek) on air–sea variability associated with ENSO teleconnections is examined via a pair of atmospheric general circulation model (AGCM) experiments. In the mixed layer model (MLM) experiment, observed sea surface temperatures (SSTs) for the years 1950–99 are specified over the tropical Pacific, while a grid of mixed layer models is coupled to the AGCM elsewhere over the global oceans. The same experimental design was used in the Ekman transport/mixed layer model (EKM) experiment with the addition of Qek in the mixed layer ocean temperature equation. The ENSO signal was evaluated using differences between composites of El Niño and La Niña events averaged over the 16 ensemble members in each experiment. In both experiments the Aleutian low deepened and the resulting surface heat fluxes cooled the central North Pacific and warmed the northeast Pacific during boreal winter in El Niño relative to La Niña events. Including Qek amplified the ENSO-related SSTs by ⅓ in the central and northeast North Pacific, producing anomalies comparable to those in nature. Differences between the ENSO-induced atmospheric circulation anomalies in the EKM and MLM experiments were not significant over the North Pacific. The sea level pressure (SLP) and SST response to ENSO over the Atlantic strongly projects on the North Atlantic Oscillation (NAO) and the SST tripole pattern in observations and both model experiments. The La Niña anomalies, which are stronger than during El Niño, include high pressure and positive SSTs in the central North Atlantic. Including Ekman transport enhanced the Atlantic SST anomalies, which in contrast to the Pacific, appeared to strengthen the overlying atmospheric circulation. M. A. Alexander J. D. Scott 2014-01-08T20:31:46Z 2014-01-08T20:31:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/978 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/978 2014-01-08T20:31:46Z Greenhouse Gas–Induced Changes in Summer Precipitation over Colorado in NARCCAP Regional Climate Models Precipitation changes between 32-yr periods in the late twentieth and mid-twenty-first centuries are investigated using regional climate model simulations provided by the North American Regional Climate Change Assessment Program (NARCCAP). The simulations generally indicate drier summers in the future over most of Colorado and the border regions of the adjoining states. The decrease in precipitation occurs despite an increase in the surface specific humidity. The domain-averaged decrease in daily summer precipitation occurs in all of the models from the 50th through the 95th percentile, but without a clear agreement on the sign of change for the most extreme (top 1% of) events. M. A. Alexander J. D. Scott K. M. Mahoney J. Barsugli 2015-10-07T14:37:27Z 2015-10-07T14:37:27Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1218 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1218 2015-10-07T14:37:27Z Moisture Pathways into the U.S. Intermountain West Associated with Heavy Winter Precipitation Events Two methods were used to identify the paths of moisture transport that reach the U.S. Intermountain West (IMW) during heavy precipitation events in winter. In the first, the top 150 precipitation events at stations located within six regions in the IMW were identified, and then back trajectories were initiated at 6-h intervals on those days at the four Climate Forecast System Reanalysis grid points nearest the stations. The second method identified the leading patterns of integrated water vapor transport (IVT) using the three leading empirical orthogonal functions of IVT over land that were first normalized by the local standard deviation. The top 1% of the associated 6-hourly time series was used to construct composites of IVT, atmospheric circulation, and precipitation. The results from both methods indicate that moisture originating from the Pacific that leads to extreme precipitation in the IMW during winter takes distinct pathways and is influenced by gaps in the Cascades (Oregon–Washington), the Sierra Nevada (California), and Peninsular Ranges (from Southern California through Baja California). The moisture transported along these routes appears to be the primary source for heavy precipitation for the mountain ranges in the IMW. The synoptic conditions associated with the dominant IVT patterns include a trough–ridge couplet at 500 hPa, with the trough located northwest of the ridge where the associated circulation funnels moisture from the west-southwest through the mountain gaps and into the IMW. M. A. Alexander J. D. Scott D. Swales M. Hughes K. M. Mahoney C. A. Smith 2012-11-08T16:42:39Z 2013-05-06T16:04:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/559 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/559 2012-11-08T16:42:39Z ENSO's Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not. M. A. Alexander H. Seo S. P. Xie J. D. Scott 2012-11-15T16:00:56Z 2013-05-07T20:01:26Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/745 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/745 2012-11-15T16:00:56Z ENSO's Impact on the Gap Wind Regions of the Eastern Tropical Pacific Ocean The recently released NCEP Climate Forecast System Reanalysis (CFSR) is used to examine the response to ENSO in the northeast tropical Pacific Ocean (NETP) during 1979–2009. The normally cool Pacific sea surface temperatures (SSTs) associated with wind jets through the gaps in the Central American mountains at Tehuantepec, Papagayo, and Panama are substantially warmer (colder) than the surrounding ocean during El Niño (La Niña) events. Ocean dynamics generate the ENSO-related SST anomalies in the gap wind regions as the surface fluxes damp the SSTs anomalies, while the Ekman heat transport is generally in quadrature with the anomalies. The ENSO-driven warming is associated with large-scale deepening of the thermocline; with the cold thermocline water at greater depths during El Niño in the NETP, it is less likely to be vertically mixed to the surface, particularly in the gap wind regions where the thermocline is normally very close to the surface. The thermocline deepening is enhanced to the south of the Costa Rica Dome in the Papagayo region, which contributes to the local ENSO-driven SST anomalies. The NETP thermocline changes are due to coastal Kelvin waves that initiate westward-propagating Rossby waves, and possibly ocean eddies, rather than by local Ekman pumping. These findings were confirmed with regional ocean model experiments: only integrations that included interannually varying ocean boundary conditions were able to simulate the thermocline deepening and localized warming in the NETP during El Niño events; the simulation with variable surface fluxes, but boundary conditions that repeated the seasonal cycle, did not. M. A. Alexander H. Seo S.-P. Xie J. D. Scott 2012-11-15T16:16:22Z 2013-05-07T20:29:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/753 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/753 2012-11-15T16:16:22Z The Atmospheric Response to Projected Terrestrial Snow Changes in the Late Twenty-First Century Two atmospheric general circulation model experiments are conducted with specified terrestrial snow conditions representative of 1980–99 and 2080–99. The snow states are obtained from twentieth-century and twenty-first-century coupled climate model integrations under increasing greenhouse gas concentrations. Sea surface temperatures, sea ice, and greenhouse gas concentrations are set to 1980–99 values in both atmospheric model experiments to isolate the effect of the snow changes. The reduction in snow cover in the twenty-first century relative to the twentieth century increases the solar radiation absorbed by the surface, and it enhances the upward longwave radiation and latent and sensible fluxes that warm the overlying atmosphere. The maximum twenty-first-century minus twentieth-century surface air temperature (SAT) differences are relatively small (<3°C) compared with those due to Arctic sea ice changes (10°C). However, they are continental in scale and are largest in fall and spring, when they make a significant contribution to the overall warming over Eurasia and North America in the twenty-first century. The circulation response to the snow changes, while of modest amplitude, involves multiple components, including a local low-level trough, remote Rossby wave trains, an annular pattern that is strongest in the stratosphere, and a hemispheric increase in geopotential height. M. A. Alexander R. Tomas C. Deser D. M. Lawrence 2012-09-25T21:00:10Z 2013-05-07T18:48:00Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/206 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/206 2012-09-25T21:00:10Z The impact of extratropical atmospheric variability on ENSO: Testing the seasonal footprinting mechanism using coupled model experiments Previous studies suggest that extratropical atmospheric variability influences the tropics via the seasonal footprinting mechanism (SFM), in which fluctuations in the North Pacific Oscillation (NPO) impact the ocean via surface heat fluxes during winter and the resulting springtime subtropical SST anomalies alter the atmosphere–ocean system over the tropics in the following summer, fall, and winter. Here, the authors test the SFM hypothesis by imposing NPO-related surface heat flux forcing in an atmospheric GCM coupled to a reduced gravity ocean model in the tropics and a slab ocean in the extratropics. The forcing is only imposed through the first winter, and then the model is free to evolve through the following winter. The evolution of the coupled model response to the forcing is consistent with the SFM hypothesis: the NPO-driven surface fluxes cause positive SST anomalies to form in the central and eastern subtropics during winter; these anomalies propagate toward the equator along with westerly wind anomalies during spring, reach the equator in summer, and then amplify, which leads to an ENSO event in the following winter. The anomalies reach the equator through a combination of thermodynamically coupled air–sea interactions, namely, the wind–evaporation–SST (WES) feedback and equatorial ocean dynamics. The initial off-equatorial anomaly propagates toward the equator through a relaxation of the climatological easterly winds south of the dominant SST anomalies, which leads to a reduction in upward latent heat flux. These westerly anomalies reach the equator during boreal summer, where they can excite downwelling equatorial Kelvin waves. The connection between off-equatorial variations and tropical ENSO-like conditions may also occur via the excitation of westward-propagating equatorial Rossby waves during spring, which reflect off of the western boundary as Kelvin waves, depressing the thermocline in the eastern Pacific during the following summer. NPO-related anomalies that form during the first winter in the tropical Pacific may also contribute to the development of an El Niño event in the following winter. The imposition of the NPO-related forcing caused warming in the ENSO region in 70% of the ensemble of 60 simulations; therefore, the response depends on the state of the tropical atmosphere–ocean system. For years where the control simulation was poised to develop into a neutral or negative ENSO event, the addition of the NPO heat fluxes tended to cause anomalous warming in the tropical Pacific in the following fall/winter; if the control was heading toward a warm ENSO event, the imposition of NPO forcing tends to reduce the amplitude of that event. M. A. Alexander D. J. Vimont P. Chang J. D. Scott 2012-09-21T23:07:05Z 2013-05-10T20:19:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/100 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/100 2012-09-21T23:07:05Z Extratropical Atmosphere-Ocean Variability in CCSM3 Extratropical atmosphere–ocean variability over the Northern Hemisphere of the Community Climate System Model version 3 (CCSM3) is examined and compared to observations. Results are presented for an extended control integration with a horizontal resolution of T85 (1.4°) for the atmosphere and land and 1° for the ocean and sea ice. Several atmospheric phenomena are investigated including storms, clouds, and patterns of variability, and their relationship to both tropical and extratropical SST anomalies. The mean storm track, the leading modes of storm track variability, and the relationship of the latter to tropical and midlatitude sea surface temperature (SST) anomalies are fairly well simulated in CCSM3. The positive correlations between extratropical SST and low-cloud anomalies in summer are reproduced by the model, but there are clear biases in the relationship between clouds and the near-surface meridional wind. The model accurately represents the circulation anomalies associated with the jet stream waveguide, the Pacific–North American (PNA) pattern, and fluctuations associated with the Aleutian low, including how the latter two features are influenced by the El Niño–Southern Oscillation (ENSO). CCSM3 has a reasonable depiction of the Pacific decadal oscillation (PDO), but it is not strongly connected to tropical Pacific SSTs as found in nature. There are biases in the position of the North Atlantic Oscillation (NAO) and other Atlantic regimes, as the mean Icelandic low in CCSM3 is stronger and displaced southeastward relative to observations. Extratropical ocean processes in CCSM3, including upper-ocean mixing, thermocline variability, and extratropical to tropical flow within the thermocline, also influence climate variability. As in observations, the model includes the "reemergence mechanism" where seasonal variability in mixed layer depth (MLD) allows SST anomalies to recur in consecutive winters without persisting through the intervening summer. Remote wind stress curl anomalies drive thermocline variability in the Kuroshio–Oyashio Extension region, which influences SST, surface heat flux anomalies, and the local wind field. The interior ocean pathways connecting the subtropics to the equator in both the Pacific and Atlantic are less pronounced in CCSM3 than in nature or in ocean-only simulations forced by observed atmospheric conditions, and the flow from the subtropical North Atlantic does not appear to reach the equator through either the western boundary or interior pathways. M. A. Alexander J. Yin G. Branstator A. Capotondi C. Cassou R. Cullather Y.-O. Kwon J. Norris J. D. Scott I. Wainer 2012-09-25T19:55:42Z 2015-04-29T14:15:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/200 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/200 2012-09-25T19:55:42Z Columnar water vapor retrievals from multifilter rotating shadowband radiometer data. The multifilter rotating shadowband radiometer (MFRSR) measures direct and diffuse irradiances in the visible and near-infrared spectral range. In addition to characteristics of atmospheric aerosols, MFRSR data also allow retrieval of precipitable water vapor (PWV) column amounts, which are determined from the direct normal irradiances in the 940-nm spectral channel. The HITRAN 2004 spectral database was used in our retrievals to model the water vapor absorption. We present a detailed error analysis describing the influence of uncertainties in instrument calibration and spectral response, as well as those in available spectral databases, on the retrieval results. The results of our PWV retrievals from the Southern Great Plains (SGP) site operated by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program were compared with correlative standard measurements by microwave radiometers (MWRs) and a global positioning system (GPS) water vapor sensor, as well as with retrievals from other solar radiometers (AERONET's CIMEL, AATS-6). Some of these data are routinely available at the SGP's Central Facility; however, we also used measurements from a wider array of instrumentations deployed at this site during the water vapor intensive observation period (WVIOP2000) in September–October 2000. The WVIOP data show better agreement between different solar radiometers or between different microwave radiometers (both groups showing relative biases within 4%) than between these two groups of instruments, with MWR values being consistently higher (up to 14%) than those from solar instruments (especially in the large PWV column amount range). We also demonstrate the feasibility of using MFRSR network data for creation of 2D data sets comparable with that of the MODIS satellite water vapor product. M. D. Alexandrov B. Schmid D. D. Turner B. Cairns V. Oinas A. A. Lacis S. I. Gutman E. R. Westwater A. Smirnov 2015-10-07T14:36:30Z 2015-10-07T14:36:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1219 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1219 2015-10-07T14:36:30Z Improved Moments Estimation for VHF Active Phased Array Radar Using Fuzzy Logic Method Various nonatmospheric signals contaminate radar wind profiler data, introducing bias into the moments and wind velocity estimation. This study applies a fuzzy logic–based method to Doppler velocity spectra to identify and eliminate the clutter echoes. This method uses mathematical analyses and a fuzzy inference system applied to each Doppler velocity spectrum to separate the atmospheric signals from the clutter. After eliminating the clutter, an adaptive algorithm is used to estimate mean Doppler velocities accurately. This combination of techniques is applied to the spectral data obtained by the newly developed 53-MHz active phased array radar located at the National Atmospheric Research Laboratory (NARL), Gadanki, India (13.5°N, 79°E). Winds derived using the conventional method and the method developed for this study are compared with those obtained by collocated GPS radiosonde. The comparison shows that the present method derives the winds more accurately compared to the conventional method. S. Allabakash P. Yasodha L. Bianco S. V. Reddy P. Srinivasulu 2012-05-04T16:02:48Z 2013-05-02T15:49:18Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/22 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/22 2012-05-04T16:02:48Z The International Atmospheric Circulation Reconstructions over the Earth (ACRE) Initiative. N/A R. Allan G. P. Compo R. Stone J. Luterbacher S. Brönnimann 2017-06-27T15:47:27Z 2017-06-27T15:47:27Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1508 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1508 2017-06-27T15:47:27Z Sea Ice Detection Using U.K. TDS-1 GNSS-R Data A sea ice detection algorithm developed using the U.K. TechDemoSat-1 (U.K. TDS-1) global navigation satellite systems (GNSSs)-reflectometry data over the Arctic and Antarctic regions is presented. It is based on measuring the similarity of the received GNSS reflected waveform or delay Doppler map (DDM) to the coherent reflection model waveform. Over the open ocean, the scattered signal has a diffusive, incoherent nature; it is described by the rough surface scattering model based on the geometric optics and the Gaussian statistics for the ocean surface slopes. Over sea ice and, in particular, newly formed sea ice, the scattered signal acquires a coherence, which is characteristic for a surface with large flat areas. In order to measure the similarity of the received waveform or DDM, to the coherent reflection model, three different estimators are presented: the normalized DDM average, the trailing edge slope (TES), and the matched filter approach. Here, a probabilistic study is presented based on a Bayesian approach using two different and independent ground-truth data sets. This approach allows one to thoroughly assess the performance of the estimators. The best results are achieved for both the TES and the matched filter approach with a probability of detection of 98.5%, a probability of false alarm of 3.6%, and a probability of error of 2.5%. However, the matched filter approach is preferred due to its simplicity. Data from AMSR2 processed using the Arctic Radiation and Turbulence Interaction STudy Sea Ice algorithm and from an Special Sensor Microwave Imager/Sounder radiometer processed by Ocean and Sea Ice SAF have been used as ground truth. A pixel has been classified as a sea ice pixel if the sea ice concentration (SIC) in it was larger than 15%. The measurement of the SIC is also assessed in this paper, but the nature of the U.K. TDS-1 data (lack of calibrated data) does not allow to make any specific conclusions about the SIC. A. Alonso-Arroyo V. U. Zavorotny A. Camps 2015-10-07T14:36:08Z 2016-04-11T20:15:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1220 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1220 2015-10-07T14:36:08Z Influence of the Madden Julian Oscillation on precipitation and surface air temperature in South America The regional influence of the Madden–Julian oscillation (MJO) on South America is described. Maps of probability of weekly-averaged rainfall exceeding the upper tercile were computed for all seasons and related statistically with the phase of the MJO as characterized by the Wheeler–Hendon real-time multivariate MJO (RMM) index and with the OLR MJO Index. The accompanying surface air temperature and circulation anomalies were also calculated. The influence of the MJO on regional scales along with their marked seasonal variations was documented. During December–February when the South American monsoon system is active, chances of enhanced rainfall are observed in southeastern South America (SESA) region mainly during RMM phases 3 and 4, accompanied by cold anomalies in the extratropics, while enhanced rainfall in the South Atlantic Convergence Zone (SACZ) region is observed in phases 8 and 1. The SESA (SACZ) signal is characterized by upper-level convergence (divergence) over tropical South America and a cyclonic (anticyclonic) anomaly near the southern tip of the continent. Impacts during March–May are similar, but attenuated in the extratropics. Conversely, in June–November, reduced rainfall and cold anomalies are observed near the coast of the SACZ region during phases 4 and 5, favored by upper-level convergence over tropical South America and an anticyclonic anomaly over southern South America. In September–November, enhanced rainfall and upper-level divergence are observed in the SACZ region during phases 7 and 8. These signals are generated primarily through the propagation of Rossby wave energy generated in the region of anomalous heating associated with the MJO. M. S. Alvarez C. S. Vera G. N. Kiladis B. Liebmann 2013-08-26T21:48:02Z 2014-07-01T16:25:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/941 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/941 2013-08-26T21:48:02Z Intraseasonal variability in South America during the cold season Intraseasonal (IS) variability in South America is analyzed during the cold season using 10–90 day bandpass filtered OLR anomalies (FOLR). IS variability explains a large percentage of variance with maximum values over Paraguay, northeastern Argentina, and southern Brazil. The leading pattern of FOLR, as isolated from an EOF analysis, (Cold Season IS pattern, CSIS), is characterized by a monopole centered over southeastern South America (SESA) with a northwest-southeast orientation. CSIS induces a large modulation on daily precipitation anomalies, especially on both wet spells and daily precipitation extremes, which are favored during positive (wet) CSIS phases. Large-Scale OLR anomalies over the tropical Indian and west Pacific Oceans associated with CSIS exhibit eastward propagation along tropical latitudes. In addition, circulation anomalies in the Southern Hemisphere reveal the presence of an anticyclonic anomaly over Antarctica with opposite-sign anomalies in middle latitudes 10 days before CSIS is maximum as well as evidence of Rossby wave-like patterns. Positive precipitation anomalies in SESA are favored during wet CSIS phases by the intensification of a cyclonic anomaly located further south, which is discernible over the southeastern Pacific for at least 14 days before CSIS peaks. The cyclonic anomaly evolution is accompanied by the intensification of an upstream anticyclonic anomaly, which remains quasi-stationary near the Antarctica Peninsula before the CSIS peak. We speculate that the stationary behavior of the anticyclonic center is favored by a hemispheric circulation anomaly pattern resembling that associated with a negative southern annular mode phase and a wavenumber 3–4 pattern at middle latitudes. M. S. Alvarez C. S. Vera G. N. Kiladis B. Liebmann 2012-11-09T17:51:02Z 2013-05-09T17:57:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/578 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/578 2012-11-09T17:51:02Z Climate and Tourism On the Colorado Plateau N/A C. Alvord B. Udall P. Long R. S. Pulwarty 2012-11-09T17:56:47Z 2013-05-08T15:35:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/579 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/579 2012-11-09T17:56:47Z Boundary layer physics over snow and ice Observations of the unique chemical environment over snow and ice in recent decades, particularly in the polar regions, have stimulated increasing interest in the boundary layer processes that mediate exchanges between the ice/snow interface and the atmosphere. This paper provides a review of the underlying concepts and examples from recent field studies in polar boundary layer meteorology, which will generally apply to atmospheric flow over snow and ice surfaces. It forms a companion paper to the chemistry review papers in this special issue of ACP that focus on processes linking halogens to the depletion of boundary layer ozone in coastal environments, mercury transport and deposition, snow photochemistry, and related snow physics. In this context, observational approaches, stable boundary layer behavior, the effects of a weak or absent diurnal cycle, and transport and mixing over the heterogeneous surfaces characteristic of coastal ocean environments are of particular relevance. P. S. Anderson W. D. Neff 2012-09-21T23:15:28Z 2013-05-10T20:20:26Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/101 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/101 2012-09-21T23:15:28Z Evaluations of the von Kármán constant in the atmospheric surface layer The von Kármán constant $k$ relates the flow speed profile in a wall-bounded shear flow to the stress at the surface. Recent laboratory studies in aerodynamically smooth flow report $k$ values that cluster around 0.42–0.43 and around 0.37–0.39. Recent data from the atmospheric boundary layer, where the flow is usually aerodynamically rough, are similarly ambiguous: $k$ is often reported to be significantly smaller than the canonical value 0.40, and two recent data sets suggest that $k$ decreases with increasing roughness Reynolds number $Re_{\ast}$. To this discussion, we bring two large atmospheric data sets that suggest $k$ is constant, 0.387$\,{\pm}\,$0.003, for $2\, {\le}\,\hbox{\it Re}_\ast \,{\le} \,100$. The data come from our yearlong deployment on Arctic sea ice during SHEBA, the experiment to study the Surface Heat Budget of the Arctic Ocean, and from over 800 h of observations over Antarctic sea ice on Ice Station Weddell (ISW). These were superb sites for atmospheric boundary-layer research; they were horizontally homogeneous, uncomplicated by topography, and unobstructed and uniform for hundreds of kilometres in all directions. During SHEBA, we instrumented a 20 m tower at five levels between 2 and 18 m with identical sonic anemometer/thermometers and, with these, measured hourly averaged values of the wind speed $U(z)$ and the stress $\tau (z)$ at each tower level $z$. On ISW, we measured the wind-speed profile with propeller anemometers at four heights between 0.5 and 4 m and measured $\tau $ with a sonic anemometer/thermometer at one height. On invoking strict quality controls, we gleaned 453 hourly $U(z)$ profiles from the SHEBA set and 100 from the ISW set. All of these profiles reflect near-neutral stratification, and each exhibits a logarithmic layer that extends over all sampling heights. By combining these profiles and our measurements of $\tau $, we made 553 independent determinations of $k$. This is, thus, the largest, most comprehensive atmospheric data set ever used to evaluate the von Kármán constant. E. L. Andreas K. J. Claffey R. E. Jordan C. W. Fairall P. S. Guest P. O. G. Persson A. A. Grachev 2012-09-25T21:12:04Z 2013-05-08T14:53:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/208 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/208 2012-09-25T21:12:04Z Parameterizing turbulent exchange over summer sea ice in the marginal ice zone The surface of the Arctic Ocean in summer is a mix of sea ice and water in both leads and melt ponds. Here we use data collected at multiple sites during the year-long experiment to study the Surface Heat Budget of the Arctic Ocean (SHEBA) to develop a bulk turbulent flux algorithm for predicting the surface fluxes of momentum and sensible and latent heat over the Arctic Ocean during summer from readily measured or modelled quantities. The distinctive aerodynamic feature of summer sea ice is that the leads and melt ponds create vertical ice faces that the wind can push against; momentum transfer to the surface is thus enhanced through form drag. In effect, summer sea ice behaves aerodynamically like the marginal ice zone, which is another surface that consists of sea ice and water. In our bulk flux algorithm, we therefore combine our SHEBA measurements of the neutral-stability drag coefficient at a reference height of 10 m, , with similar measurements from marginal ice zones that have been reported in the literature to create a unified parametrization for for summer sea ice and for any marginal ice zone. This parametrization predicts from a second-order polynomial in ice concentration. Our bulk flux algorithm also includes expressions for the roughness lengths for temperature and humidity, introduces new profile stratification corrections for stable stratification, and effectively eliminates the singularities that often occur in iterative flux algorithms for very light winds. In summary, this new algorithm seems capable of estimating the friction velocity u* (a surrogate for the momentum flux) over summer sea ice with an absolute accuracy of 0.02–0.03 m s−1; the sensible heat flux, with an accuracy of about 6 W m−2; and the latent heat flux, with an accuracy of 3.5 W m−2. E. L. Andreas T. W. Horst A. A. Grachev P. O. G. Persson C. W. Fairall P. S. Guest R. E. Jordan 2012-11-15T16:20:30Z 2013-05-07T23:18:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/754 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/754 2012-11-15T16:20:30Z Production velocity of sea spray droplets The sea spray generation function dF/dr0 predicts the rate at which droplets of initial radius r0 are produced at the sea surface. Because this function is not readily measurable in the marine environment, however, it is often inferred from measurements of the near-surface droplet concentration, C(r0), through an assumed velocity scale, the effective spray production velocity. This paper proceeds in reverse, though: It uses a reliable estimate of dF/dr0 and 13 sets of measurements of C(r0) over the ocean to calculate the implied effective production velocity, Veff, for droplets with initial radii r0 from 5 to 300 μm. It then compares these Veff values with four candidate expressions for this production velocity: the dry-deposition velocity, VDh; the mean wind speed at the significant wave amplitude (A1/3), the standard deviation in vertical droplet velocity, σwd; and laboratory measurements of the ejection velocity of jet droplets, Vej. The velocity scales and Vej agree best with the implied Veff values for 20 ≤ r0 ≤ 300 μm. The deposition velocity, VDh, which is the velocity most commonly used in this application, agrees worst with the Veff values. For droplets with r0 less than about 20 μm, the analysis also rejects the main hypothesis: that dF/dr0 and C(r0) can be related through a velocity scale. These smaller droplets simply have residence times that are too long for spray concentrations to be in local equilibrium with the spray production rate. E. L. Andreas K. F. Jones C. W. Fairall 2012-11-09T18:42:25Z 2013-05-08T15:37:15Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/580 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/580 2012-11-09T18:42:25Z A Bulk Turbulent Air–Sea Flux Algorithm for High-Wind, Spray Conditions Sensible and latent heat can cross the air–sea interface by two routes: as interfacial fluxes controlled by molecular processes right at the interface, and as spray fluxes from the surface of sea spray droplets. Once the 10-m wind speed over the ocean reaches approximately 11–13 m s−1, the spray sensible and latent heat fluxes become significant fractions (i.e., 10% or greater) of the corresponding interfacial fluxes. The analysis here establishes that result by combining the Tropical Ocean-Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (COARE) version 2.6 bulk interfacial flux algorithm with a microphysical spray model to partition measured heat fluxes from two good high-wind datasets into spray and interfacial flux contributions. The measurements come from the Humidity Exchange over the Sea (HEXOS) experiment and the Fronts and Atlantic Storm-Tracks Experiment (FASTEX); wind speeds in these two datasets span 5 to 20 m s−1. After the measured heat fluxes are separated into spray and interfacial contributions, the spray fluxes are used to develop a fast spray flux algorithm to combine with the COARE version 2.6 interfacial flux algorithm in a unified turbulent surface flux algorithm for use in large-scale and ocean storm models. A sensitivity analysis of the spray and interfacial components of this unified flux algorithm demonstrates how the two component fluxes scale differently with the mean meteorological variables and why they must therefore be parameterized separately in models intended to treat air–sea fluxes in high winds. E. L. Andreas P. O. G. Persson J. E. Hare 2012-09-25T21:05:58Z 2013-05-08T14:53:40Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/207 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/207 2012-09-25T21:05:58Z Parameterizing turbulent exchange over sea ice in winter The Surface Heat Budget of the Arctic Ocean (SHEBA) experiment produced 18 000 h of turbulence data from the atmospheric surface layer over sea ice while the ice camp drifted for a year in the Beaufort Gyre. Multiple sites instrumented during SHEBA suggest only two aerodynamic seasons over sea ice. In "winter" (October 1997 through 14 May 1998 and 15 September 1998 through the end of the SHEBA deployment in early October 1998), the ice was compact and snow covered, and the snow was dry enough to drift and blow. In "summer" (15 May through 14 September 1998 in this dataset), the snow melted, and melt ponds and leads appeared and covered as much as 40% of the surface with open water. This paper develops a bulk turbulent flux algorithm to explain the winter data. This algorithm predicts the surface fluxes of momentum, and sensible and latent heat from more readily measured or modeled quantities. A main result of the analysis is that the roughness length for wind speed z0 does not depend on the friction velocity u* in the drifting snow regime (u* ≥ 0.30 m s−1) but, rather, is constant in the SHEBA dataset at about 2.3 × 10−4 m. Previous analyses that found z0 to increase with u* during drifting snow may have suffered from fictitious correlation because u* also appears in z0. The present analysis mitigates this fictitious correlation by plotting measured z0 against the corresponding u* computed from the bulk flux algorithm. Such plots, created with data from six different SHEBA sites, show z0 to be independent of the bulk u* for 0.15 < u* ≤ 0.65 m s−1. This study also evaluates the roughness lengths for temperature zT and humidity zQ, incorporates new profile stratification corrections for stable stratification, addresses the singularities that often occur in iterative flux algorithms in very light winds, and includes an extensive analysis of whether atmospheric stratification affects z0, zT, and zQ. E. L. Andreas P. O. G. Persson R. E. Jordan T. W. Horst P. S. Guest A. A. Grachev C. W. Fairall 2015-04-23T16:42:33Z 2015-04-29T14:48:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1140 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1140 2015-04-23T16:42:33Z CO2, CO, and CH4 measurements from tall towers in the NOAA Earth System Research Laboratory's Global Greenhouse Gas Reference Network: instrumentation, uncertainty analysis, and recommendations for future high-accuracy greenhouse gas monitoring efforts A reliable and precise in situ CO2 and CO analysis system has been developed and deployed at eight sites in the NOAA Earth System Research Laboratory's (ESRL) Global Greenhouse Gas Reference Network. The network uses very tall (> 300 m) television and radio transmitter towers that provide a convenient platform for mid-boundary-layer trace-gas sampling. Each analyzer has three sample inlets for profile sampling, and a complete vertical profile is obtained every 15 min. The instrument suite at one site has been augmented with a cavity ring-down spectrometer for measuring CO2 and CH4. The long-term stability of the systems in the field is typically better than 0.1 ppm for CO2, 6 ppb for CO, and 0.5 ppb for CH4, as determined from repeated standard gas measurements. The instrumentation is fully automated and includes sensors for measuring a variety of status parameters, such as temperatures, pressures, and flow rates, that are inputs for automated alerts and quality control algorithms. Detailed and time-dependent uncertainty estimates have been constructed for all of the gases, and the uncertainty framework could be readily adapted to other species or analysis systems. The design emphasizes use of off-the-shelf parts and modularity to facilitate network operations and ease of maintenance. The systems report high-quality data with > 93% uptime. Recurrent problems and limitations of the current system are discussed along with general recommendations for high-accuracy trace-gas monitoring. The network is a key component of the North American Carbon Program and a useful model for future research-grade operational greenhouse gas monitoring efforts. A. E. Andrews . . . D. Wolfe J.W. Munger P. P. Tans 2013-01-31T21:15:51Z 2013-04-24T17:40:27Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/878 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/878 2013-01-31T21:15:51Z Meteorological Model Evaluation for CalNex 2010 The performance of mesoscale meteorological models is evaluated for the coastal zone and Los Angeles area of Southern California, and for the San Joaquin Valley. Several configurations of the Weather Research and Forecasting Model (WRF) with differing grid spacing, initialization, planetary boundary layer (PBL) physics, and land surface models are compared. One configuration of the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model is also included, providing results from an independent development and process flow. Specific phenomena of interest for air quality studies are examined. All model configurations are biased toward higher wind speeds than observed. The diurnal cycle of wind direction and speed (land–sea-breeze cycle) as modeled and observed by a wind profiler at Los Angeles International Airport is examined. Each of the models shows different flaws in the cycle. Soundings from San Nicolas Island, a case study involving the Research Vessel (R/V) Atlantis and the NOAA P3 aircraft, and satellite images are used to evaluate simulation performance for cloudy boundary layers. In a case study, the boundary layer structure over the water is poorly simulated by all of the WRF configurations except one with the total energy–mass flux boundary layer scheme and ECMWF reanalysis. The original WRF configuration had a substantial bias toward low PBL heights in the San Joaquin Valley, which are improved in the final configuration. WRF runs with 12-km grids have larger errors in wind speed and direction than those present in the 4-km grid runs. W. M. Angevine L. Eddington K. Durkee C. W. Fairall L. Bianco J. Brioude 2012-09-21T23:33:58Z 2013-05-10T20:15:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/103 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/103 2012-09-21T23:33:58Z Structure and formation of the highly stable marine boundary layer over the Gulf of Maine A shallow, stable boundary layer is ubiquitous over the cool waters of the Gulf of Maine in summer. This layer affects pollutant transport throughout the region by isolating overlying flow from the surface. In this paper, we explore how the stable boundary layer is formed and describe its characteristics. The temperature profile of the lowest 1–2 km of the atmosphere over the Gulf of Maine is remarkably similar regardless of transport time over water or the time of day when the flow left the land, provided only that the flow is offshore. This similarity is forced by the (roughly) constant water temperature and the (roughly) constant temperature of the free troposphere over the continent. However, the processes leading to the similar profiles are quite different depending on the time of day when the flow crosses the coast. Air leaving the coast at night already has a stable profile, whereas air leaving the coast at midday or afternoon has a deep mixed layer. In the latter case, the stable layer formation over the water is of interest. Using observations of surface fluxes, profiles, and winds on the NOAA Research Vessel Ronald H. Brown from the 2004 International Consortium for Atmospheric Research in Transport and Transformation (ICARTT)/New England Air Quality Study, we show that the formation of the stable layer, which involves cooling a roughly 50- to 100-m-deep layer by 5–15 K, occurs within 10 km and a half hour after leaving the coast. The internal boundary layer near shore is deeper than predicted by standard relationships. Historical data are explored and also show deeper internal boundary layers than predicted. We also describe one exceptional case where a 200-m-deep neutral layer was observed and discuss the degree of isolation of the stable boundary layer and its duration. W. M. Angevine J. E. Hare C. W. Fairall D. Wolfe R. J. Hill W. A. Brewer A. B. White 2016-10-06T22:26:18Z 2016-10-06T22:26:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1392 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1392 2016-10-06T22:26:18Z Contributions of different time scales to extreme Paraná floods The present study provides the first complete examination of how different time scales contributed to generate the four largest observed floods of the Paraná River (1905, 1983, 1992 and 1998). This inspection is based on the results from a previous study where an empirical method was used to decompose a 1904–2010 Paraná flow record (monthly means) into several physically meaningful oscillations with distinctive time scales or periods (few months to decades), and a secular increasing trend. We show that all the oscillations largely contributed to the four extreme floods, except an 18-year cycle that did not contribute to the 1992 flood. Sporadic intense constructive interferences between interannual-to-interdecadal (3–85 years) cycles determined (i) the favorable conditions for extreme-flood occurrence, and (ii) notable differences among floods. Indeed, in 1983, the largest flood ever recorded resulted mainly from an exceptionally strong constructive interference between cycles of 3–5, 9, 18 and 31–85 years, which are related to El Niño events, the North Atlantic Oscillation, the South Atlantic Convergence Zone, and the Pacific Ocean, respectively. Contributions of the 31–85-year cycle to the two biggest floods (1983 and 1992) are larger than the contributions of the secular upward trend, suggesting the importance of this slow oscillation in flood formation processes. The implications of our results for understanding and predicting Paraná floods are discussed. A. Antico M. E. Torres H. F. Diaz 2012-10-15T23:21:08Z 2013-05-07T17:25:13Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/292 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/292 2012-10-15T23:21:08Z Internal solitons in the ocean and their effect on underwater sound Nonlinear internal waves in the ocean are discussed (a) from the standpoint of soliton theory and (b) from the viewpoint of experimental measurements. First, theoretical models for internal solitary waves in the ocean are briefly described. Various nonlinear analytical solutions are treated, commencing with the well-known Boussinesq and Korteweg–de Vries equations. Then certain generalizations are considered, including effects of cubic nonlinearity, Earth's rotation, cylindrical divergence, dissipation, shear flows, and others. Recent theoretical models for strongly nonlinear internal waves are outlined. Second, examples of experimental evidence for the existence of solitons in the upper ocean are presented; the data include radar and optical images and in situ measurements of wave forms, propagation speeds, and dispersion characteristics. Third, and finally, action of internal solitons on sound wave propagation is discussed. This review paper is intended for researchers from diverse backgrounds, including acousticians, who may not be familiar in detail with soliton theory. Thus, it includes an outline of the basics of soliton theory. At the same time, recent theoretical and observational results are described which can also make this review useful for mainstream oceanographers and theoreticians. J. R. Apel L. A. Ostrovsky Y. A. Stepanyants 2016-10-13T18:44:46Z 2016-10-13T18:44:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1395 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1395 2016-10-13T18:44:46Z Measurement of wind profiles by motion-stabilised ship-borne Doppler lidar Three months of Doppler lidar wind measurements were obtained during the Arctic Cloud Summer Experiment on the icebreaker Oden during the summer of 2014. Such ship-borne Doppler measurements require active stabilisation to remove the effects of ship motion. We demonstrate that the combination of a commercial Doppler lidar with a custom-made motion-stabilisation platform enables the retrieval of wind profiles in the Arctic atmospheric boundary layer during both cruising and ice-breaking with statistical uncertainties comparable to land-based measurements. This held true particularly within the atmospheric boundary layer even though the overall aerosol load was very low. Motion stabilisation was successful for high wind speeds in open water and the resulting wave conditions. It allows for the retrieval of vertical winds with a random error below 0.2 m s−1. The comparison of lidar-measured wind and radio soundings gives a mean bias of 0.3 m s−1 (2°) and a mean standard deviation of 1.1 m s−1 (12°) for wind speed (wind direction). The agreement for wind direction degrades with height. The combination of a motion-stabilised platform with a low-maintenance autonomous Doppler lidar has the potential to enable continuous long-term high-resolution ship-based wind profile measurements over the oceans. P. Archtert I. M. Brooks B. J. Brooks B. I. Moat J. Prytherch P. O. G. Persson M. Tjernström 2017-05-05T19:39:49Z 2017-05-05T19:45:23Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1489 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1489 2017-05-05T19:39:49Z Measuring ocean waves in sea ice using SAR imagery: A quasi-deterministic approach evaluated with Sentinel-1 and in situ data Measurements of wave heights in marginal ice zones are limited to very few in situ data. Here we revisit the linear and quasilinear theories of Synthetic Aperture Radar imaging of waves in the particular case of waves in sea ice. Instead of only working with spectra, we have developed an iterative nonlinear algorithm to estimate phase-resolved deterministic maps of wave-induced orbital velocities, from which elevation spectra can be derived. Application of this algorithm to Sentinel 1A wave mode images in the Southern Ocean shows that it produces reasonable results for swells in all directions except when they propagate at a few degrees off the range direction. The estimate of wave parameters is expected to work best when the shortest wave components, those which cause a pixel displacement of the order of the dominant wavelength in azimuth, can be neglected. Otherwise short waves produce a blurring of the image, increasing exponentially with the azimuthal wavenumber and reducing the estimated wave amplitude. Given the expected spatial attenuation of waves in ice-covered regions, our deterministic method should apply beyond a few tens of kilometers in the ice, without any correction for short wave effects. In situ data collected around the ice edge as part of the 2015 SeaState DRI cruise in the Beaufort confirm the progressive image blurring caused by such short waves, and the apparent reduction in the wave modulation. When short waves propagate from the open ocean towards the ice, this blurring can produce an unrealistic apparent increase of wave height, from the open ocean up to a few tens of kilometers inside the ice. F. Ardhuin J. Stopa B. Chapron F. Collard M. Smith M. D. Thomson B. W. Blomquist P. O. G. Persson C. O. Collins P. Wadhams 2016-04-11T20:21:51Z 2016-10-06T21:57:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1308 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1308 2016-04-11T20:21:51Z Aerosol size distribution seasonal characteristics measured in Tiksi, Russian Arctic Four years of continuous aerosol number size distribution measurements from the Arctic Climate Observatory in Tiksi, Russia, are analyzed. Tiksi is located in a region where in situ information on aerosol particle properties has not been previously available. Particle size distributions were measured with a differential mobility particle sizer (in the diameter range of 7–500 nm) and with an aerodynamic particle sizer (in the diameter range of 0.5–10 μm). Source region effects on particle modal features and number, and mass concentrations are presented for different seasons. The monthly median total aerosol number concentration in Tiksi ranges from 184 cm−3 in November to 724 cm−3 in July, with a local maximum in March of 481 cm−3. The total mass concentration has a distinct maximum in February–March of 1.72–2.38 μg m−3 and two minimums in June (0.42 μg m−3) and in September–October (0.36–0.57 μg m−3). These seasonal cycles in number and mass concentrations are related to isolated processes and phenomena such as Arctic haze in early spring, which increases accumulation and coarse-mode numbers, and secondary particle formation in spring and summer, which affects the nucleation and Aitken mode particle concentrations. Secondary particle formation was frequently observed in Tiksi and was shown to be slightly more common in marine, in comparison to continental, air flows. Particle formation rates were the highest in spring, while the particle growth rates peaked in summer. These results suggest two different origins for secondary particles, anthropogenic pollution being the important source in spring and biogenic emissions being significant in summer. The impact of temperature-dependent natural emissions on aerosol and cloud condensation nuclei numbers was significant: the increase in both the particle mass and the CCN (cloud condensation nuclei) number with temperature was found to be higher than in any previous study done over the boreal forest region. In addition to the precursor emissions of biogenic volatile organic compounds, the frequent Siberian forest fires, although far away, are suggested to play a role in Arctic aerosol composition during the warmest months. Five fire events were isolated based on clustering analysis, and the particle mass and cloud condensation nuclei number were shown to be somewhat affected by these events. In addition, during calm and cold months, aerosol concentrations were occasionally increased by local aerosol sources in trapping inversions. These results provide valuable information on interannual cycles and sources of Arctic aerosols. E. Asmi V. Kondratyev D. Brus . . . T. Uttal V. Ivakhov A. Makshtas 2012-11-13T17:00:02Z 2013-05-02T16:24:31Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/610 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/610 2012-11-13T17:00:02Z Detection of Asian dust in California orographic precipitation Aerosols impact the microphysical properties of clouds by serving as cloud condensation nuclei (CCN) and ice nuclei (IN). By modifying cloud properties, aerosols have the potential to alter the location and intensity of precipitation, but determining the magnitude and reproducibility of aerosol-induced changes to precipitation remains a significant challenge to experimentalists and modelers. During the CalWater Early Start campaign (22 February to 11 March 2009), a uniquely comprehensive set of atmospheric chemistry, precipitation, and meteorological measurements were made during two extratropical cyclones. These two storms showed enhanced integrated water vapor concentrations and horizontal water vapor transports due to atmospheric river conditions and, together, produced 23% of the annual precipitation and 38% of the maximum snowpack at California's Central Sierra Snow Lab (CSSL). Precipitation measurements of insoluble residues showed very different chemistry occurring during the two storms with the first one showing mostly organic species from biomass burning, whereas the second storm showed a transition from biomass burning organics to the dominance of Asian dust. As shown herein, the dust was transported across the Pacific during the second storm and became incorporated into the colder high-altitude precipitating orographic clouds over the Sierra Nevada. The second storm produced 1.4 times as much precipitation and increased the snowpack by 1.6 times at CSSL relative to the first storm. As described in previous measurement and modeling studies, dust can effectively serve as ice nuclei, leading to increased riming rates and enhanced precipitation efficiency, which ultimately can contribute to differences in precipitation. Future modeling studies will help deconvolute the meteorological, microphysical, and aerosol factors leading to these differences and will use CalWater's meteorological and aerosol observations to constrain the model-based interpretations. The ultimate goal of such combined efforts is to use the results to improve aerosol-cloud impacts on precipitation in regional climate models. A. P. Ault C. R. Williams A. B. White P. J. Neiman . . . F. M. Ralph et al. 2014-01-09T00:40:18Z 2014-01-09T00:40:18Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1007 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1007 2014-01-09T00:40:18Z Characterizing decadal to centennial variability in the equatorial Pacific during the last millennium The magnitude of sea surface temperature variability in the NINO3.4 region of the equatorial Pacific on decadal and longer timescales is assessed in observational data, state-of-the-art (Coupled Model Intercomparison Project 5) climate model simulations, and a new ensemble of paleoclimate reconstructions. On decadal to multidecadal timescales, variability in these records is consistent with the null hypothesis that it arises from "multivariate red noise" (a multivariate Ornstein-Uhlenbeck process) generated from a linear inverse model of tropical ocean-atmosphere dynamics. On centennial and longer timescales, both a last millennium simulation performed using the Community Climate System Model 4 (CCSM4) and the paleoclimate reconstructions have variability that is significantly stronger than the null hypothesis. However, the time series of the model and the reconstruction do not agree with each other. In the model, variability primarily reflects a thermodynamic response to reconstructed solar and volcanic activity, whereas in the reconstruction, variability arises from either internal climate processes, forced responses that differ from those in CCSM4, or nonclimatic proxy processes that are not yet understood. These findings imply that the response of the tropical Pacific to future forcings may be even more uncertain than portrayed by state-of-the-art models because there are potentially important sources of century-scale variability that these models do not simulate. T. R. Ault C. Deser M. Newman J. Emile-Geay 2012-09-25T21:15:00Z 2013-05-08T14:52:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/209 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/209 2012-09-25T21:15:00Z Are we successfully adapting science to climate change? N/A K. Averyt 2015-04-24T17:13:27Z 2015-04-29T14:47:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1144 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1144 2015-04-24T17:13:27Z An In Situ Method for Sizing Insoluble Residues in Precipitation and Other Aqueous Samples Particles are frequently incorporated into clouds or precipitation, influencing climate by acting as cloud condensation or ice nuclei, taking up coatings during cloud processing, and removing species through wet deposition. Many of these particles, particularly ice nuclei, can remain suspended within cloud droplets/crystals as insoluble residues. While previous studies have measured the soluble or bulk mass of species within clouds and precipitation, no studies to date have determined the number concentration and size distribution of insoluble residues in precipitation or cloud water using in situ methods. Herein, for the first time we demonstrate that nanoparticle tracking analysis (NTA) is a powerful in situ method for determining the total number concentration, number size distribution, and surface area distribution of insoluble residues in precipitation, both of rain and melted snow. The method uses 500 μL or less of liquid sample and does not require sample modification. Number concentrations for the insoluble residues in aqueous precipitation samples ranged from 2.0–3.0 (±0.3) × 108 particles cm−3, while surface area ranged from 1.8 (±0.7)–3.2 (±1.0) × 107 μm2 cm−3. Number size distributions peaked between 133 and 150 nm, with both single and multi-modal character, while surface area distributions peaked between 173 and 270 nm. Comparison with electron microscopy of particles up to 10 μm show that, by number, >97% residues are <1 μm in diameter, the upper limit of the NTA. The range of concentration and distribution properties indicates that insoluble residue properties vary with ambient aerosol concentrations, cloud microphysics, and meteorological dynamics. NTA has great potential for studying the role that insoluble residues play in critical atmospheric processes. J. L. Axson J. M. Creamean A. L. Bondy S. S. Capracotta K. Y. Warner A. P. Ault 2016-04-11T20:25:10Z 2016-04-11T20:25:10Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1309 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1309 2016-04-11T20:25:10Z Transported Mineral Dust Deposition Case Study at a Hydrologically Sensitive Mountain Site: Size and Composition Shifts in Ambient Aerosol and Snowpack Transported mineral dust deposition to remote mountain snow decreases snow albedo and increases absorption of solar radiation, which accelerates snowpack melt and alters water supply. Mineralogy and chemical composition determine dust particle optical properties, which vary by source region. While impacts of dust deposition at remote mountain sites have been established, few studies have connected the chemical composition of ambient particles during deposition events with the properties of those deposited on the snowpack. Ambient particles and surface snow were sampled in the San Juan Mountains of southwestern Colorado, which frequently experiences dust deposition in the spring and has evidence of dust-enhanced snow melt. Individual particles were analyzed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The number concentration and size distribution of insoluble residues in the top level of snow were determined with nanoparticle tracking analysis (NTA). During a minor dust event (April 2–3, 2015), the fraction of absorbing iron-enriched dust in the ambient aerosol, the number concentration, and size of insoluble residues in snow all increased. This can be traced to shifts in mineral dust source region within the Colorado Plateau, during which, there were higher wind speeds leading to increased transport. The shift in chemical composition and mineralogy of the transported dust has the potential to impact snowpack radiative forcing during dry deposition. In addition, it can also modify the snowpack through scavenging of particles during wet deposition, as well as alter the properties of clouds and orographic precipitation. Understanding these impacts is crucial to understanding the hydrological cycle at remote mountain sites. J. L. Axson H. Shen A. L. Bondy C. C. Landry J. Welz J. M. Creamean 2017-04-13T21:30:53Z 2017-04-13T21:30:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1487 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1487 2017-04-13T21:30:53Z Assessment of an atmospheric transport model for annual inverse estimates of California greenhouse gas emissions Atmospheric inverse estimates of gas emissions depend on transport model predictions, hence driving a need to assess uncertainties in the transport model. In this study we assess the uncertainty in WRF-STILT (Weather Research and Forecasting and Stochastic Time-Inverted Lagrangian Transport) model predictions using a combination of meteorological and carbon monoxide (CO) measurements. WRF configurations were selected to minimize meteorological biases using meteorological measurements of winds and boundary layer depths from surface stations and radar wind profiler sites across California. We compare model predictions with CO measurements from four tower sites in California from June 2013 through May 2014 to assess the seasonal biases and random errors in predicted CO mixing ratios. In general, the seasonal mean biases in boundary layer wind speed (< ~ 0.5 m/s), direction (< ~ 15°), and boundary layer height (< ~ 200 m) were small. However, random errors were large (~1.5–3.0 m/s for wind speed, ~ 40–60° for wind direction, and ~ 300–500 m for boundary layer height). Regression analysis of predicted and measured CO yielded near-unity slopes (i.e., within 1.0 ± 0.20) for the majority of sites and seasons, though a subset of sites and seasons exhibit larger (~30%) uncertainty, particularly when weak winds combined with complex terrain in the South Central Valley of California. Looking across sites and seasons, these results suggest that WRF-STILT simulations are sufficient to estimate emissions of CO to up to 15% on annual time scales across California. J. E. Badgley S. Jeong X. Cui S. Newman J. Zhang C. Priest M. Campos-Pineda A. E. Andrews L. Bianco M. Lloyd N. Lareau C. Clements M. L. Fischer 2012-09-25T20:34:51Z 2013-08-28T17:20:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/201 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/201 2012-09-25T20:34:51Z Use of the Koppen-Trewartha climate classification to evaluate climatic refugia in statistically derived ecoregions for the People's Republic of China Changes in climate as projected by state-of-the-art climate models are likely to result in novel combinations of climate and topo-edaphic factors that will have substantial impacts on the distribution and persistence of natural vegetation and animal species. We have used multivariate techniques to quantify some of these changes; the method employed was the Multivariate Spatio-Temporal Clustering (MSTC) algorithm. We used the MSTC to quantitatively define ecoregions for the People's Republic of China for historical and projected future climates. Using the Köppen–Trewartha classification system we were able to quantify some of the temperature and precipitation relationships of the ecoregions. We then tested the hypothesis that impacts to environments will be lower for ecoregions that retain their approximate geographic locations. Our results showed that climate in 2050, as projected from anthropogenic forcings using the Hadley Centre HadCM3 general circulation model, were sufficient to create novel environmental conditions even where ecoregions remained spatially stable; cluster number was found to be of paramount importance in detecting novelty. Continental-scale analyses are generally able to locate potentially static ecoregions but they may be insufficient to define the position of those reserves at a grid cell-by-grid cell basis. B. Baker H. F. Diaz W. Hargrove F. Hoffman 2016-10-06T22:30:18Z 2016-10-06T22:30:18Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1393 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1393 2016-10-06T22:30:18Z Long-range correlations of microseism-band pressure fluctuations in the ocean We investigate the spatial coherence of underwater ambient noise using a yearlong time-series measured off Ascension Island. Qualitative agreement with observed cross-correlations is achieved using a simple range-dependent model, constrained by earlier, active tomographic studies in the area. In particular, the model correctly predicts the existence of two weakly dispersive normal modes in the microseism frequency range, with the group speed of one of the normal modes being smaller than the sound speed in water. The agreement justifies our interpretation of the peaks of the measured cross-correlation function of ambient noise as modal arrivals, with dispersion that is sensitive to crustal velocity structure. Our observations are consistent with Scholte to Moho head wave coupled propagation, with double mode conversion occurring due to the bathymetric variations between receivers. We thus demonstrate the feasibility of interrogating crustal properties using noise interferometry of moored hydrophone data at ranges in excess of 120 km. J. S. Ball O. A. Godin L. G. Evers C. Lv 2014-07-15T18:19:39Z 2014-07-15T18:19:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1053 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1053 2014-07-15T18:19:39Z Hydroclimate variability and change in the Prairie Pothole Region: The "duck factory" of North America The Prairie Pothole Region (PPR) of the Northern Great Plains is a vital ecosystem responsible each year for producing 50-80% of new recruits to the North American duck population. Climate variability and change can impact the hydrology and ecology of the region with implications for waterfowl populations. The historical relationship between PPR wetlands, duck populations, and seasonal hydroclimate are explored. Model experiments from the Coupled Model Intercomparison Project Phase 5 are used to determine whether a recent wetting trend is due to natural variability or changing climate and how PPR hydroclimate will change into the future. Year-to-year variations in May duck populations, pond numbers and Palmer Drought Severity Index are well correlated over past decades. Pond and duck numbers tend to increase in spring following La Niña events, but the correlation is not strong. Model simulations suggest that the strengthening of the precipitation gradient across the PPR over the past century is predominantly due to natural variability and therefore could reverse. Model projections of future climate indicate precipitation will increase across the PPR in all seasons except summer, but this gain for surface moisture is largely offset by increased evapotranspiration due to higher temperatures and increased atmospheric evaporative demand. In summer, the combined effects of warming and precipitation changes indicate seasonal surface drying in the future. The presented hydroclimate analyses produce potential inputs to ecological and hydrological simulations of PPR wetlands to inform risk analysis of how this North American waterfowl habitat will evolve in the future, providing guidance to land managers facing conservation decisions. T. Ballard R. Seager J. E. Smerdon B. I. Cook A. J. Ray 2015-04-20T20:58:09Z 2015-04-29T14:52:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1121 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1121 2015-04-20T20:58:09Z Hydroclimate Variability and Change in the Prairie Pothole Region, the "Duck Factory" of North America The Prairie Pothole Region (PPR) of the northern Great Plains is a vital ecosystem responsible each year for producing 50%–80% of new recruits to the North American duck population. Climate variability and change can impact the hydrology and ecology of the region with implications for waterfowl populations. The historical relationship between PPR wetlands, duck populations, and seasonal hydroclimate are explored. Model experiments from phase 5 of the Coupled Model Intercomparison Project are used to determine whether a recent wetting trend is due to natural variability or changing climate and how PPR hydroclimate will change into the future. Year-to-year variations in May duck populations, pond numbers, and the Palmer drought severity index are well correlated over past decades. Pond and duck numbers tend to increase in spring following La Niña events, but the correlation is not strong. Model simulations suggest that the strengthening of the precipitation gradient across the PPR over the past century is predominantly due to natural variability and therefore could reverse. Model projections of future climate indicate precipitation will increase across the PPR in all seasons except summer, but this gain for surface moisture is largely offset by increased evapotranspiration because of higher temperatures and increased atmospheric evaporative demand. In summer, the combined effects of warming and precipitation changes indicate seasonal surface drying in the future. The presented hydroclimate analyses produce potential inputs to ecological and hydrological simulations of PPR wetlands to inform risk analysis of how this North American waterfowl habitat will evolve in the future, providing guidance to land managers facing conservation decisions. T. Ballard R. Seager J. E. Smerdon B. I. Cook A. J. Ray B. Rajagopalan Y. Kushnir J. Nakamura N. Henderson 2012-11-13T17:05:08Z 2013-05-02T16:25:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/611 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/611 2012-11-13T17:05:08Z Dependence of daily peak O3 concentrations near Houston, Texas on environmental factors: Wind speed, temperature, and boundary-layer depth Airborne and surface measurements of ozone (O3) during the Texas Air Quality Study campaigns in 2000 and 2006 (TexAQS 2000 and TexAQS 2006) were used to investigate the relationship between maximum daily O3 and the vector-averaged wind speed <U>, calculated from radar wind profiler data, in the lower atmospheric boundary layer (BL). Both the maximum daily O3 and the peak "add-on" O3 contribution (calculated as the maximum minus the background values) from the Houston area showed a strong correlation (r∼0.7–0.9) with both the reciprocal of this wind speed <U>−1, and the wind speed <U> itself. Data from airborne platforms produced higher correlations in general than surface-measured values. Except for special cases where O3 was measured close to source activity in a location where the BL depth h was suppressed, peak daily ozone concentrations were not strongly correlated with h, and attempts to include 1/h dependence with <U>−1 degraded the correlations—indicating that in general, h was not a strong predictor for maximum daily O3. Inclusion of daily maximum temperature in the regression analysis also failed to improve the correlations significantly. The high correlations for wind speed thus showed that <U> was the meteorological variable most strongly associated with peak daily O3 concentrations. The best-fit regression line of peak daily O3 vs. <U> for the 2000 data lay above the line for 2006 for wind speeds less than 5 m s−1, the difference increasing as the wind speeds weakened. This six-year decrease in O3 concentrations for the weakest-wind, most polluted days suggests that control strategies implemented between 2000 and 2006 may be producing beneficial effects, especially on the most polluted days. R. M. Banta C. J. Senff R. J. Alvarez . . . L. S. Darby . . . A. B. White 2013-01-31T21:27:48Z 2013-04-24T17:25:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/879 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/879 2013-01-31T21:27:48Z Observational Techniques: Sampling the Mountain Atmosphere In this chapter several types of instruments are surveyed that have contributed to increased understanding of the structure of atmospheric flows and processes that drive these flows in complex terrain. After a brief example of the use of in-situ measurements, those that are in contact with the air they are measuring, a review of basic remote sensing principles serves as a background for a discussion of several types of remote sensors. The review focuses on active remote sensing systems, those that transmit and receive their own signal, including sodar, radar, radar wind profilers, and lidar. Examples of the kind of data available from each type of system allow an appreciation for how these systems contribute to advanced understanding of atmospheric processes by providing data above the surface and revealing the evolving vertical and horizontal structure of complex terrain flows. Advantages of deploying combinations of complementary instruments are described. The roles of measurements and mesoscale numerical models are discussed in a section where modeling studies have used high-resolution remote sensing and other advanced measurement systems to verify the models. Finally a brief section describes turbulence measurement techniques by remote sensing that may be able to provide profiles of turbulence quantities in mountain studies. R. M. Banta C. M. Shun D. C. Law . . . M. J. Post L. S. Darby 2012-05-03T16:52:00Z 2013-05-02T15:41:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/19 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/19 2012-05-03T16:52:00Z Parameterizations of sea-spray impact on the air-sea momentum and heat fluxes This paper focuses on parameterizing the effect of sea spray at hurricane-strength winds on the momentum and heat fluxes in weather prediction models using the Monin–Obukhov similarity theory (a common framework for the parameterizations of air–sea fluxes). In this scheme, the mass-density effect of sea spray is considered as an additional modification to the stratification of the near-surface profiles of wind, temperature, and moisture in the marine surface boundary layer (MSBL). The overall impact of sea-spray droplets on the mean profiles of wind, temperature, and moisture depends on the wind speed at the level of sea-spray generation. As the wind speed increases, the mean droplet size and the mass flux of sea-spray increase, rendering an increase of stability in the MSBL and the leveling-off of the surface drag. Sea spray also tends to increase the total air–sea sensible and latent heat fluxes at high winds. Results from sensitivity testing of the scheme in a numerical weather prediction model for an idealized case of hurricane intensification are presented along with a dynamical interpretation of the impact of the parameterized sea-spray physics on the structure of the hurricane boundary layer. J.-W. Bao C. W. Fairall S. A. Michelson L. Bianco J.-W. Bao 2013-01-31T21:30:43Z 2013-04-24T17:40:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/880 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/880 2013-01-31T21:30:43Z Impact of Physics Representations in the HWRFX on Simulated Hurricane Structure and Pressure–Wind Relationships A series of idealized experiments with the NOAA Experimental Hurricane Weather Research and Forecasting Model (HWRFX) are performed to examine the sensitivity of idealized tropical cyclone (TC) intensification to various parameterization schemes of the boundary layer (BL), subgrid convection, cloud microphysics, and radiation. Results from all the experiments are compared in terms of the maximum surface 10-m wind (VMAX) and minimum sea level pressure (PMIN)—operational metrics of TC intensity—as well as the azimuthally averaged temporal and spatial structure of the tangential wind and its material acceleration. The conventional metrics of TC intensity (VMAX and PMIN) are found to be insufficient to reveal the sensitivity of the simulated TC to variations in model physics. Comparisons of the sensitivity runs indicate that (i) different boundary layer physics parameterization schemes for vertical subgrid turbulence mixing lead to differences not only in the intensity evolution in terms of VMAX and PMIN, but also in the structural characteristics of the simulated tropical cyclone; (ii) the surface drag coefficient is a key parameter that controls the VMAX–PMIN relationship near the surface; and (iii) different microphysics and subgrid convection parameterization schemes, because of their different realizations of diabatic heating distribution, lead to significant variations in the vortex structure. The quantitative aspects of these results indicate that the current uncertainties in the BL mixing, surface drag, and microphysics parameterization schemes have comparable impacts on the intensity and structure of simulated TCs. The results also indicate that there is a need to include structural parameters in the HWRFX evaluation. J.-W. Bao S. G. Gopalakrishnan S. A. Michelson F. D. Marks M. T. Montgomery 2016-10-06T22:34:14Z 2016-10-06T22:34:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1394 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1394 2016-10-06T22:34:14Z Pathways to the Production of Precipitating Hydrometeors and Tropical Cyclone Development Pathways to the production of precipitation in two cloud microphysics schemes available in the Weather Research and Forecasting (WRF) Model are investigated in a scenario of tropical cyclone intensification. Comparisons of the results from the WRF Model simulations indicate that the variation in the simulated initial rapid intensification of an idealized tropical cyclone is due to the differences between the two cloud microphysics schemes in their representations of pathways to the formation and growth of precipitating hydrometeors. Diagnoses of the source and sink terms of the hydrometeor budget equations indicate that the major differences in the production of hydrometeors between the schemes are in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes, such as accretion growth and sedimentation. These differences lead to different horizontally averaged vertical profiles of net latent heating rate associated with significantly different horizontally averaged vertical distributions and production rates of hydrometeors in the simulated clouds. Results from this study also highlight the possibility that the advantage of double-moment formulations can be overshadowed by the uncertainties in the spectral definition of individual hydrometeor categories and spectrum-dependent microphysical processes. J.-W. Bao S. A. Michelson E. D. Grell 2012-07-11T16:14:22Z 2013-05-07T19:08:31Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/29 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/29 2012-07-11T16:14:22Z Meteorological evaluation of a weather-chemistry forecasting model using observations from the TEXAS AQS 2000 field experiment Meteorological forecasts for the period of 25–30 August 2000 from a coupled weather-chemistry model are evaluated both qualitatively and quantitatively using the observations from different instruments that were deployed in metropolitan Houston during the Texas Air-Quality Study 2000 field experiment. The qualitative comparison is carried out with respect to the meteorological processes associated with the influence of the large-scale flow on the sea breeze that are essential to the development of the surface ozone exceedances over Houston, while the quantitative comparison is focused on the errors and uncertainties of the forecasts. The qualitative comparison is performed with respect to a conceptual model for the influence of the large-scale flow on the sea breeze. The comparison shows that although the overall forecasted influence of the large-scale flow on the sea breeze compares qualitatively well to the observations, quantitative differences do exist between the forecasted and observed wind speed and direction, as well as with temperature and moisture. It is found that the forecasted low-level winds have a systematic easterly bias and the forecasted low-level temperature has a cold bias. The errors in the forecasted low-level moisture appear relatively small, but with a cold bias they lead to higher relative humidity in the forecast than in reality. There is great sensitivity of the model forecasted low-level winds to different initial conditions. The quantitative comparison also indicates that the model's effective horizontal resolution corresponding to 1.67-km grid spacing is actually about 10 km. J.-W. Bao S. A. Michelson S. A. McKeen G. A. Grell 2012-09-21T23:39:28Z 2013-05-10T20:01:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/104 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/104 2012-09-21T23:39:28Z Interpretation of Enhanced Integrated Water Vapor Bands Associated with Extratropical Cyclones: Their Formation and Connection to Tropical Moisture Trajectory analysis using a weather prediction model is performed for five cases to interpret the formation of enhanced bands of vertically integrated water vapor (IWV) in the central and eastern Pacific that are frequently seen in satellite images from the Special Sensor Microwave Imager. The connection of these enhanced bands with poleward water vapor transport from the Tropics is also examined. It is shown that the leading end of the enhanced IWV bands (defined as the most eastward and poleward end) is the manifestation of moisture convergence in the warm conveyor belt associated with extratropical cyclones, while the bands away from the leading end result mainly from moisture convergence along the trailing cold fronts. There is evidence that some enhanced IWV bands may be associated with a direct poleward transport of tropical moisture along the IWV bands from the Tropics all the way to the extratropics. The trajectory analysis, together with the seasonal mean sea level pressure analysis, indicates that a favorable condition for the occurrence of a direct, along-IWV band transport of tropical (defined as south of 23.5°N) moisture to the U.S. West Coast in the eastern Pacific is a weakened subtropical ridge in the central Pacific with an enhanced southwesterly low-level flow. The authors hypothesize that the direct poleward transport of tropical moisture within an enhanced IWV band in the eastern Pacific is most possible in the neutral El Niño–Southern Oscillation (ENSO) phase and is least possible in the El Niño phase. J.-W. Bao S. A. Michelson P. J. Neiman F. M. Ralph J. M. Wilczak 2012-11-09T18:47:29Z 2013-05-08T15:36:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/581 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/581 2012-11-09T18:47:29Z Observed and WRF-Simulated Low-Level Winds in a High-Ozone Episode during the Central California Ozone Study A case study is carried out for the 29 July–3 August 2000 episode of the Central California Ozone Study (CCOS), a typical summertime high-ozone event in the Central Valley of California. The focus of the study is on the low-level winds that control the transport and dispersion of pollutants in the Central Valley. An analysis of surface and wind profiler observations from the CCOS field experiment indicates a number of important low-level flows in the Central Valley: 1) the incoming low-level marine airflow through the Carquinez Strait into the Sacramento River delta, 2) the diurnal cycle of upslope–downslope flows, 3) the up- and down-valley flow in the Sacramento Valley, 4) the nocturnal low-level jet in the San Joaquin Valley, and 5) the orographically induced mesoscale eddies (the Fresno and Schultz eddies). A numerical simulation using the advanced research version of the Weather Research and Forecasting Model (WRF) reproduces the overall pattern of the observed low-level flows. The physical reasons behind the quantitative differences between the observed and simulated low-level winds are also analyzed and discussed, although not enough observations are available to diagnose thoroughly the model-error sources. In particular, hodograph analysis is applied to provide physical insight into the impact of the large-scale, upper-level winds on the locally forced low-level winds. It is found that the diurnal rotation of the observed and simulated hodographs of the local winds varies spatially in the Central Valley, resulting from the combining effect of topographically induced local forcing and the interaction between the upper-level winds and the aforementioned low-level flows. The trajectory analysis not only further confirms that WRF reproduces the observed low-level transport processes reasonably well but also shows that the simulated upper-level winds have noticeable errors. The results from this study strongly suggest that the errors in the WRF-simulated low-level winds are related not only to the errors in the model's surface conditions and atmospheric boundary layer physics but also to the errors in the upper-level forcing mostly prescribed in the model's lateral boundary conditions. J.-W. Bao S. A. Michelson P. O. G. Persson et al. 2014-01-08T20:34:50Z 2014-01-08T20:34:50Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/979 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/979 2014-01-08T20:34:50Z Planning for an Uncertain Future: Climate Change Sensitivity Assessment toward Adaptation Planning for Public Water Supply Assessing climate change risk to municipal water supplies is often conducted by hydrologic modeling specific to local watersheds and infrastructure to ensure that outputs are compatible with existing planning frameworks and processes. This study leverages the modeling capacity of an operational National Weather Service River Forecast Center to explore the potential impacts of future climate-driven hydrologic changes on factors important to planning at the Salt Lake City Department of Public Utilities (SLC). Hydrologic modeling results for the study area align with prior research in showing that temperature changes alone will lead to earlier runoff and reduced runoff volume. The sensitivity of average annual flow to temperature varies significantly between watersheds, averaging −3.8% °F−1 and ranging from −1.8% to −6.5% flow reduction per degree Fahrenheit of warming. The largest flow reductions occur during the high water demand months of May–September. Precipitation drives hydrologic response more strongly than temperature, with each 1% precipitation change producing an average 1.9% runoff change of the same sign. This paper explores the consequences of climate change for the reliability of SLC's water supply system using scenarios that include hydrologic changes in average conditions, severe drought scenarios, and future water demand test cases. The most significant water management impacts will be earlier and reduced runoff volume, which threaten the system's ability to maintain adequate streamflow and storage to meet late-summer water demands. T. Bardsley A. Wood M. T. Hobbins et al. 2012-09-25T21:27:41Z 2013-05-08T14:58:40Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/211 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/211 2012-09-25T21:27:41Z Determination of oceanic ozone deposition by ship-borne eddy covariance flux measurements A fast response ozone analyzer based on the ozone-nitric oxide chemiluminescence method was integrated into the NOAA-ESRL flux system to achieve the first ship-borne, direct ozone flux measurements over the open ocean. Air was collected from an inlet at 18 m height over the ocean surface mounted to the bow-jackstaff and via a 30 m-long sampling line to the ozone instrument on the ship deck. A "puff" system was used for accurate and regular determination of the sample transport time (lag) between the inlet and the chemical analyzer. A Nafion-membrane dryer facilitated removal of fast water vapor fluctuations, which eliminated the need for quenching and density correction of the ozone signal. The sampling-analyzer system was found to have a ~0.25–0.40 s response time at a sensitivity of ~2800 counts s−1 per ppbv of ozone. Quality control and data filtering procedures for eliminating data that did not meet measurement requirements were critically evaluated. The new ozone flux system was deployed aboard the NOAA Ship Ronald H. Brown, and evaluated using results obtained during several research cruises off the coasts of the North and South America continents, yielding ozone deposition velocities (mean ± standard error) ranging from 0.009±0.001 cm s−1 to 0.24±0.020 cm s−1. L. Baritreau D. Helmig C. W. Fairall J. E. Hare J. Hueber E. K. Lang 2012-11-09T18:54:43Z 2013-05-08T15:37:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/582 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/582 2012-11-09T18:54:43Z The Monte Carlo Independent Column Approximation: an assessment using several global atmospheric models The Monte Carlo Independent Column Approximation (McICA) computes domain-average, broadband radiative flux profiles within conventional global climate models (GCMs). While McICA is unbiased with respect to the full ICA, it generates, as a by-product, random noise. If this by-product leads to statistically significant impacts on GCM simulations, it could limit the usefulness of McICA. This paper assesses the impact of McICA's random noise on six GCMs. To this end, the GCMs performed ensembles of 14-day long simulations for various renditions of McICA, each with differing amounts of random noise. As seen in the past, low-cloud fraction and surface temperature were affected most by noise. However, all GCM simulations using operationally viable renditions of McICA showed no statistically significant impacts, even for precipitation - a highly intermittent variable that one might expect to be sensitive to random fluctuations. Two GCMs showed statistically significant responses using an academic version of McICA that generates overly large sampling noise. Time series analyses of high-resolution (i.e. typically 2-hourly) data revealed that fluctuations associated with most variables and GCMs are immune to McICA noise. Moreover, the nature of these fluctuations can vary substantially among GCMs and most often they overwhelm any noise impacts. Overall, the results presented here corroborate a range of previous studies done on one GCM at a time: random noise produced by recommended versions of McICA has statistically insignificant effects on GCM simulations. Copyright © 2008 Royal Meteorological Society and Her Majesty in Right of Canada. H. W. Barker J. Cole J.-J. Morcrette R. Pincus et al. 2016-04-11T20:27:48Z 2016-04-11T20:27:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1310 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1310 2016-04-11T20:27:48Z Drought in the Middle East and Central–Southwest Asia During Winter 2013/14 N/A M. Barlow A. Hoell 2012-07-11T22:06:10Z 2014-07-22T20:35:26Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/97 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/97 2012-07-11T22:06:10Z Improving seasonal prediction practices through attribution of climate variability The Seasonal Diagnostics Consortium of the Applied Research Centers is engaging in a real-time activity to detect and understand the role of sea surface temperature (SST) anomalies in observed climate anomalies. The activity is aimed to improve practices in seasonal climate forecasting by fully harvesting the accumulated research evidence of the climate's sensitivity to ocean forcing. The approach, in the first phase of the activity, involves performing ensembles of atmospheric general circulation models (AGCMs) at several institutions, using the most recently observed global SST anomalies as prescribed forcings. The runs are routinely updated each month as the latest SST observations become available, adding to the archive of historical simulations spanning the last half-century. The SST-forced signal in the seasonal mean climate is detected through the agreement among ensemble mean anomalies drawn from the simulations of the various AGCMs. The consortium activity also compares the dynamically forced signals with those estimated empirically, based on the observational archive. A comparison of the coordinated simulations with the observed climate anomalies is then made for two principal reasons: 1) to offer an attribution for the ocean's role in the origin of the observed seasonal climate anomalies, and 2) to determine the causes for success or failure of operational seasonal climate predictions, whose tools may be either mainly dynamically or empirically derived. It is expected that routine climate diagnostics and attribution efforts for climate anomalies will help further develop the knowledge base for improving the practice of seasonal climate predictions, and advance understanding of global climate on seasonal to decadal time scales. A. G. Barnston A. Kumar L Goddard M. P. Hoerling 2012-09-28T20:52:44Z 2014-01-08T21:03:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/203 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/203 2012-09-28T20:52:44Z Comment on "Global warming and United States landfalling hurricanes" by Chunzai Wang and Sang-Ki Lee. N/A J. J. Barsugli 2014-01-08T20:39:35Z 2014-01-08T20:58:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/980 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/980 2014-01-08T20:39:35Z The Practitioner's Dilemma: How to Assess the Credibility of Downscaled Climate Projections Suppose you are a city planner, regional water manager, or wildlife conservation specialist who is asked to include the potential impacts of climate variability and change in your risk management and planning efforts. What climate information would you use? The choice is often regional or local climate projections downscaled from global climate models (GCMs; also known as general circulation models) to include detail at spatial and temporal scales that align with those of the decision problem. A few years ago this information was hard to come by. Now there is Web-based access to a proliferation of high-resolution climate projections derived with differing downscaling methods. J. J. Barsugli G. Guentchev R. M. Horton . . . A. J. Ray et al. 2012-09-28T20:54:52Z 2014-01-08T21:04:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/276 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/276 2012-09-28T20:54:52Z Comment on " When will Lake Mead go dry?" by T. P. Barnett and D. W. Pierce. N/A J. J. Barsugli K. Nowak B. Rajagopalan J. R. Prarie B. Harding 2012-09-21T23:42:32Z 2014-01-08T21:00:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/105 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/105 2012-09-21T23:42:32Z Sensitivity of global warming to the pattern of tropical ocean warming The current generations of climate models are in substantial disagreement as to the projected patterns of sea surface temperatures (SSTs) in the Tropics over the next several decades. We show that the spatial patterns of tropical ocean temperature trends have a strong influence on global mean temperature and precipitation and on global mean radiative forcing. We identify the SST patterns with the greatest influence on the global mean climate and find very different, and often opposing, sensitivities to SST changes in the tropical Indian and West Pacific Oceans. Our work stresses the need to reduce climate model biases in these sensitive regions, as they not only affect the regional climates of the nearby densely populated continents, but also have a disproportionately large effect on the global climate. J. J. Barsugli S.-I. Shin P. D. Sardeshmukh 2012-07-11T16:11:17Z 2014-01-08T20:59:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/32 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/32 2012-07-11T16:11:17Z Tropical climate regimes and global climate sensitivity in a simple setting Multiple tropical climate regimes are found in an atmospheric general circulation model (AGCM) coupled to a global slab ocean when the model is forced by different values of globally uniform insolation. Even in this simple setting, convection organizes into an intertropical convergence zone (ITCZ) solely due to the effect of planetary rotation, as was found in Kirtman and Schneider, for a single value of insolation. Here the response to a range of insolation values is explored, and surprisingly, multiple climate regimes characterized by radically different ITCZ structures are found. In order from the coldest to warmest climates, these are a symmetric double ITCZ, a near-symmetric equatorial ITCZ, a transient asymmetric ITCZ, and a stable, strongly asymmetric ITCZ. The model exhibits hysteresis in the transition from the near-symmetric to the strongly asymmetric ITCZ regimes when insolation is increased and then decreased. The initial transition away from symmetry can occur in the absence of air–sea coupling; however, the coupling is essential for the establishment and maintenance of the strongly asymmetric ITCZ. Wind–evaporation–SST feedback as well as the longwave radiative effects of clouds and water vapor on SSTs appear to be important in maintaining the asymmetric regime. The existence of multiple regimes in a single AGCM, and the dependence of these regimes on SST feedbacks, may have a bearing on the ITCZ simulation errors of current coupled climate models. The sensitivity of the global mean surface temperature generally decreases with increasing insolation, a consequence primarily of increasingly negative shortwave cloud forcing. Climate sensitivity measured across a regime transition can be much larger than the sensitivity within a single regime. J. J. Barsugli S.-I. Shin P. D. Sardeshmukh 2012-12-21T20:19:37Z 2013-05-06T16:34:38Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/842 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/842 2012-12-21T20:19:37Z Two Faces of Uncertainty: Climate Science and Water Utility Planning Methods N/A J. J. Barsugli J. M. Vogel L. Kaatz J. B. Smith M. Waage C. J. Anderson 2016-04-11T20:52:19Z 2016-04-11T21:58:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1311 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1311 2016-04-11T20:52:19Z Improving Flash Flood Forecasts: The HMT-WPC Flash Flood and Intense Rainfall Experiment Despite advancements in numerical modeling and the increasing prevalence of convection-allowing guidance, flash flood forecasting remains a substantial challenge. Accurate flash flood forecasts depend not only on accurate quantitative precipitation forecasts (QPFs), but also on an understanding of the corresponding hydrologic response. To advance forecast skill, innovative guidance products that blend meteorology and hydrology are needed, as well as a comprehensive verification dataset to identify areas in need of improvement. To address these challenges, in 2013 the Hydrometeorological Testbed at the Weather Prediction Center (HMT-WPC), partnering with the National Severe Storms Laboratory (NSSL) and the Earth System Research Laboratory (ESRL), developed and hosted the inaugural Flash Flood and Intense Rainfall (FFaIR) Experiment. In its first two years, the experiment has focused on ways to combine meteorological guidance with available hydrologic information. One example of this is the creation of neighborhood flash flood guidance (FFG) exceedance probabilities, which combine QPF information from convection-allowing ensembles with flash flood guidance; these were found to provide valuable information about the flash flood threat across the contiguous United States. Additionally, WPC has begun to address the challenge of flash flood verification by developing a verification database that incorporates observations from a variety of disparate sources in an attempt to build a comprehensive picture of flash flooding across the nation. While the development of this database represents an important step forward in the verification of flash flood forecasts, many of the other challenges identified during the experiment will require a long-term community effort in order to make notable advancements. F. E. Barthold T. E. Workoff B. A. Cosgrove J. J. Gourley D. R. Novak K. M. Mahoney 2015-10-28T22:49:53Z 2016-10-13T18:47:49Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1281 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1281 2015-10-28T22:49:53Z Aspects of ECMWF model performance in polar areas Global numerical weather prediction skill over polar areas is assessed, mostly based on the European Centre for Medium-Range Weather Forecasts (ECMWF) system but also the Met Office, Japan Meteorological Agency (JMA), Environment Canada and National Centers for Environmental Prediction (NCEP) analysis data. Polar forecast verification against analyses shows a similar trend of forecast improvement over the past 12 years compared with improvements at lower latitudes. These improvements are presumably due to increased model resolution and model sophistication, improved data assimilation methods and increased observational data coverage and better data quality. By comparing ECMWF's real-time forecast skill changes against those from reforecasts initialized from reanalyses, it is possible to quantify how much of the improvement is from system improvements and how much is attributable to weather variability. Ensemble skill also improved over time and, again, consistently across latitudes. The quality of analyses serving for forecast verification and initialization has been investigated further. An intercomparison of The Observing system Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) analyses and forecasts revealed substantial differences for surface parameters, but also at lower levels in the troposphere, where most of the physical processes relevant to weather in the short-to-medium range take place over the poles. The differences between the TIGGE analyses were generally much larger than differences between members of the ECMWF 4D-Var ensemble of analyses generated internally at ECMWF. This suggests that neither the multi-analysis approach nor ensemble data assimilation may represent polar analysis uncertainty properly. This is particularly visible at the surface and lower levels in the atmosphere. Forecast spread and error match much better north of 65∘N where less atmospheric variability prevails along the entire forecast range, while in areas of significant synoptic activity the spread also appears too low. P. Bauer L. Magnusson J.-N. Thépaut T. M. Hamill 2015-04-24T17:18:48Z 2015-10-06T22:27:24Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1145 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1145 2015-04-24T17:18:48Z Verification of Quantitative Precipitation Reforecasts over the Southeastern United States NOAA's second-generation reforecasts are approximately consistent with the operational version of the 2012 NOAA Global Ensemble Forecast System (GEFS). The reforecasts allow verification to be performed across a multidecadal time period using a static model, in contrast to verifications performed using an ever-evolving operational modeling system. This contribution examines three commonly used verification metrics for reforecasts of precipitation over the southeastern United States: equitable threat score, bias, and ranked probability skill score. Analysis of the verification metrics highlights the variation in the ability of the GEFS to predict precipitation across amount, season, forecast lead time, and location. Beyond day 5.5, there is little useful skill in quantitative precipitation forecasts (QPFs) or probabilistic QPFs. For lighter precipitation thresholds [e.g., 5 and 10 mm (24 h)−1], use of the ensemble mean adds about 10% to the forecast skill over the deterministic control. QPFs have increased in accuracy from 1985 to 2013, likely due to improvements in observations. Results of this investigation are a first step toward using the reforecast database to distinguish weather regimes that the GEFS typically predicts well from those regimes that the GEFS typically predicts poorly. M. A. Baxter G. M. Lackmann K. M. Mahoney T. E. Workoff T. M. Hamill 2012-11-06T17:36:20Z 2013-05-07T19:10:24Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/484 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/484 2012-11-06T17:36:20Z Low-frequency atmospheric acoustic energy associated with vortices produced by thunderstorms An infrasonic observatory collocated with the Colorado State University CHILL radar during the summer of 1995 permitted unique comparisons between severe storm kinematics and detected acoustic energy at subaudible frequencies near 1 Hz. Radar observations of a velocity couplet aloft (evolving into a tornado) showed a circulation maximum descending for about 30 min while moving to the east. The detected infrasound followed the trend of these observations. A model of sound radiated from vortex systems predicts frequencies in the range observed. These data are interpreted in the context of past infrasonic observations. An ongoing study comparing regional tornado and funnel sightings with archived infrasonic data has identified over 100 cases to date where the infrasonic signals occurred at the time of, and from the direction of, the vortices. For some of these cases, the distances were greater than 100 km. The author and his associates continue to collect datasets to permit further evaluation of infrasonic detection methods. A. J. Bedard 2012-11-15T16:29:03Z 2013-05-08T14:57:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/756 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/756 2012-11-15T16:29:03Z Meteorology, Chapter 257 This chapter reviews impacts on aircraft posed by a variety of atmospheric phenomena covering a large range of altitudes, scale sizes, and origins. Such weather hazards can be regional, long-duration fields of turbulence or, on the other hand, concentrated, short-duration microbursts. Accident statistics indicate the frequency and severities of encounters with various types of weather. A review of key weather features describes physical processes involved. Methods for prediction and warning discussed suggest hazard mitigation approaches and areas of need for further research. A. J. Bedard 2014-01-08T20:43:28Z 2014-01-08T20:43:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/981 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/981 2014-01-08T20:43:28Z Infrasonic ray tracing applied to mesoscale atmospheric structures: Refraction by hurricanes A ray-tracing program is used to estimate the refraction of infrasound by the temperature structure of the atmosphere and by hurricanes represented by a Rankine-combined vortex wind plus a temperature perturbation. Refraction by the hurricane winds is significant, giving rise to regions of focusing, defocusing, and virtual sources. The refraction of infrasound by the temperature anomaly associated with a hurricane is small, probably no larger than that from uncertainties in the wind field. The results are pertinent to interpreting ocean wave generated infrasound in the vicinities of tropical cyclones. A. J. Bedard R. M. Jones 2016-04-11T21:06:17Z 2016-04-11T21:06:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1314 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1314 2016-04-11T21:06:17Z On the Quantification of Atmospheric Rivers Precipitation from Space: Composite Assessments and Case Studies over the Eastern North Pacific Ocean and the Western United States Atmospheric rivers (ARs) are often associated with extreme precipitation, which can lead to flooding or alleviate droughts. A decade (2003–12) of landfalling ARs impacting the North American west coast (between 32.5° and 52.5°N) is collected to assess the skill of five commonly used satellite-based precipitation products [T3B42, T3B42 real-time (T3B42RT), CPC morphing technique (CMORPH), PERSIANN, and PERSIANN–Cloud Classification System (CCS)] in capturing ARs' precipitation rate and pattern. AR detection was carried out using a database containing twice-daily satellite-based integrated water vapor composite observations. It was found that satellite products are more consistent over ocean than land and often significantly underestimate precipitation rate over land compared to ground observations. Incorrect detection of precipitation from IR-based methods is prevalent over snow and ice surfaces where microwave estimates often show underestimation or missing data. Bias adjustment using ground observation is found very effective to improve satellite products, but it also raises concern regarding near-real-time applicability of satellite products for ARs. The analysis using individual case studies (6–8 January and 13–14 October 2009) and an ensemble of AR events suggests that further advancement in capturing orographic precipitation and precipitation over cold and frozen surfaces is needed to more reliably quantify AR precipitation from space. A. Behrangi B. Guan P. J. Neiman M. Schreier B. Lambrigtsen 2013-04-12T22:23:26Z 2013-04-24T17:26:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/900 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/900 2013-04-12T22:23:26Z July 2012 Greenland melt extent enhanced by low-level liquid clouds Melting of the world's major ice sheets can affect human and environmental conditions by contributing to sea-level rise. In July 2012, an historically rare period of extended surface melting was observed across almost the entire Greenland ice sheet, raising questions about the frequency and spatial extent of such events. Here we show that low-level clouds consisting of liquid water droplets ('liquid clouds'), via their radiative effects, played a key part in this melt event by increasing near-surface temperatures. We used a suite of surface-based observations, remote sensing data, and a surface energy-balance model. At the critical surface melt time, the clouds were optically thick enough and low enough to enhance the downwelling infrared flux at the surface. At the same time they were optically thin enough to allow sufficient solar radiation to penetrate through them and raise surface temperatures above the melting point. Outside this narrow range in cloud optical thickness, the radiative contribution to the surface energy budget would have been diminished, and the spatial extent of this melting event would have been smaller. We further show that these thin, low-level liquid clouds occur frequently, both over Greenland and across the Arctic, being present around 30–50 per cent of the time. Our results may help to explain the difficulties that global climate models have in simulating the Arctic surface energy budget, particularly as models tend to under-predict the formation of optically thin liquid clouds at supercooled temperatures—a process potentially necessary to account fully for temperature feedbacks in a warming Arctic climate. R. Bennartz M. D. Shupe D. D. Turner et al. 2013-04-12T22:32:10Z 2013-04-24T17:26:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/901 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/901 2013-04-12T22:32:10Z El Niño-Southern Oscillation impacts on winter winds over Southern California Changes in wintertime 10 m winds due to the El Niño-Southern Oscillation are examined using a 6 km resolution climate simulation of Southern California covering the period from 1959 through 2001. Wind speed statistics based on regional averages reveal a general signal of increased mean wind speeds and wind speed variability during El Niño across the region. An opposite and nearly as strong signal of decreased wind speed variability during La Niña is also found. These signals are generally more significant than the better-known signals in precipitation. In spite of these regional-scale generalizations, there are significant sub-regional mesoscale structures in the wind speed impacts. In some cases, impacts on mean winds and wind variability at the sub-regional scale are opposite to those of the region as a whole. All of these signals can be interpreted in terms of shifts in occurrences of the region's main wind regimes due to the El Niño phenomenon. The results of this study can be used to understand how interannual wind speed variations in regions of Southern California are influenced by the El Niño phenomenon. N. Berg A. Hall S. B. Capps M. Hughes 2016-10-27T22:59:45Z 2016-10-27T23:02:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1444 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1444 2016-10-27T22:59:45Z Surface-atmosphere decoupling limits accumulation at Summit, Greenland Despite rapid melting in the coastal regions of the Greenland Ice Sheet, a significant area (~40%) of the ice sheet rarely experiences surface melting. In these regions, the controls on annual accumulation are poorly constrained owing to surface conditions (for example, surface clouds, blowing snow, and surface inversions), which render moisture flux estimates from myriad approaches (that is, eddy covariance, remote sensing, and direct observations) highly uncertain. Accumulation is partially determined by the temperature dependence of saturation vapor pressure, which influences the maximum humidity of air parcels reaching the ice sheet interior. However, independent proxies for surface temperature and accumulation from ice cores show that the response of accumulation to temperature is variable and not generally consistent with a purely thermodynamic control. Using three years of stable water vapor isotope profiles from a high altitude site on the Greenland Ice Sheet, we show that as the boundary layer becomes increasingly stable, a decoupling between the ice sheet and atmosphere occurs. The limited interaction between the ice sheet surface and free tropospheric air reduces the capacity for surface condensation to achieve the rate set by the humidity of the air parcels reaching interior Greenland. The isolation of the surface also acts to recycle sublimated moisture by recondensing it onto fog particles, which returns the moisture back to the surface through gravitational settling. The observations highlight a unique mechanism by which ice sheet mass is conserved, which has implications for understanding both past and future changes in accumulation rate and the isotopic signal in ice cores from Greenland. M. Berkelhammer D. C. Noone H. C. Steen-Larsen A. Bailey C. J. Cox M. S. O'Neill D. Schneider K. Steffen J. W. C. White 2016-11-10T15:07:07Z 2017-04-11T19:32:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1447 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1447 2016-11-10T15:07:07Z Stochastic Parameterization: Towards a new view of Weather and Climate Models Stochastic parameterizations - empirically derived, or based on rigorous mathematical and statistical concepts - have great potential to increase the predictive capability of next generation weather and climate models. The last decade has seen the success of stochastic parameterizations in short-term, medium-range and seasonal forecasts: operational weather centers now routinely use stochastic parameterization schemes to better represent model inadequacy and improve the quantification of forecast uncertainty. Developed initially for numerical weather prediction, the inclusion of stochastic parameterizations not only provides better estimates of uncertainty, but it is also extremely promising for reducing longstanding climate biases and relevant for determining the climate response to external forcing. This article highlights recent developments from different research groups which show that the stochastic representation of unresolved processes in the atmosphere, oceans, land surface and cryosphere of comprehensive weather and climate models (a) gives rise to more reliable probabilistic forecasts of weather and climate and (b) reduces systematic model bias. We make a case that the use of mathematically stringent methods for the derivation of stochastic dynamic equations will lead to substantial improvements in our ability to accurately simulate weather and climate at all scales. Recent work in mathematics, statistical mechanics and turbulence is reviewed, its relevance for the climate problem demonstrated, and future research directions outlined. J. Berner U. Achatz L. Batté . . . C. Penland et al. 2012-11-13T17:11:14Z 2013-05-02T16:26:00Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/612 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/612 2012-11-13T17:11:14Z Impact of Sea-Spray on the Atmospheric Surface Layer The feedback effects of sea-spray on the heat and momentum fluxes under equilibrium conditions associated with winds of tropical cyclones are investigated using a one-dimensional coupled sea-spray and atmospheric surface-layer (ASL) model. This model is capable of simulating the microphysical aspects of the evaporation of saline water droplets of various sizes and their dynamic and thermal interaction with the turbulence mixing that is simulated by the Mellor–Yamada 1.5-order closure scheme. Sea-spray droplet generation is described by a state-of-the-art parametrization that predicts the size spectrum of sea-spray droplets for a given surface forcing. The results from a series of simulations indicate the way in which evaporating droplets of various sizes modify the turbulence mixing near the surface, which in turn affects further droplet evaporation. All these results are direct consequences of the effects of sea-spray on the balance of turbulent kinetic energy in the spray-filled surface layer. In particular, the overall impact of sea-spray droplets on the mean wind depends on the wind speed at the level of sea-spray generation. When the wind speed is below 40 m s−1, the droplets are small in size and tend to evaporate substantially and thus cool the spray-filled layer, while for wind speeds above 50 m s−1, the size of the droplets is so large that they do not have enough time to evaporate much before falling back into the sea. The sensible heat carried by the droplets is released to the ambient air, increasing the buoyancy of the surface layer and enhancing the turbulent mixing. The suspension of sea-spray droplets reduces the buoyancy and makes the surface layer more stable, decreasing the friction velocity and the downward turbulent mixing of momentum. The results from the numerical experiments also suggest that, in order not to violate the constant flux assumption critical to the Monin–Obukhov similarity theory, a displacement equal to the mean wave height should be included in the logarithmic profiles of the wind and thermal fields. L. Bianco J.-W. Bao C. W. Fairall S. A. Michelson 2012-11-06T17:41:38Z 2013-05-07T19:11:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/485 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/485 2012-11-06T17:41:38Z Combining microwave radiometer and wind profiler radar measurements for high-resolution atmospheric humidity profiling A self-consistent remote sensing physical method to retrieve atmospheric humidity high-resolution profiles by synergetic use of a microwave radiometer profiler (MWRP) and wind profiler radar (WPR) is illustrated. The proposed technique is based on the processing of WPR data for estimating the potential refractivity gradient profiles and their optimal combination with MWRP estimates of potential temperature profiles in order to fully retrieve humidity gradient profiles. The combined algorithm makes use of recent developments in WPR signal processing, computing the zeroth-, first-, and second-order moments of WPR Doppler spectra via a fuzzy logic method, which provides quality control of radar data in the spectral domain. On the other hand, the application of neural network to brightness temperatures, measured by a multichannel MWRP, can provide continuous estimates of tropospheric temperature and humidity profiles. Performance of the combined algorithm in retrieving humidity profiles is compared with simultaneous in situ radiosonde observations (raob's). The empirical sets of WPR and MWRP data were collected at the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains (SGP) site. Combined microwave radiometer and wind profiler measurements show encouraging results and significantly improve the spatial vertical resolution of atmospheric humidity profiles. Finally, some of the limitations found in the use of this technique and possible future improvements are also discussed. L. Bianco D. Cimini 2012-11-13T17:13:43Z 2013-05-02T16:26:38Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/613 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/613 2012-11-13T17:13:43Z Diurnal Evolution and Annual Variability of Boundary-Layer Height and Its Correlation to Other Meteorological Variables in California's Central Valley One year of observations from a network of five 915-MHz boundary-layer radar wind profilers equipped with radio acoustic sounding systems located in California's Central Valley are used to investigate the annual variability of convective boundary-layer depth and its correlation to meteorological parameters and conditions. Results from the analysis show that at four of the sites, the boundary-layer height reaches its maximum in the late-spring months then surprisingly decreases during the summer months, with mean July depths almost identical to those for December. The temporal decrease in boundary-layer depth, as well as its spatial variation, is found to be consistent with the nocturnal low-level lapse rate observed at each site. Multiple forcing mechanisms that could explain the unexpected seasonal behaviour of boundary-layer depth are investigated, including solar radiation, precipitation, boundary-layer mesoscale convergence, low-level cold-air advection, local surface characteristics and irrigation patterns and synoptic-scale subsidence. Variations in solar radiation, precipitation and synoptic-scale subsidence do not explain the shallow summertime convective boundary-layer depths observed. Topographically forced cold-air advection and local land-use characteristics can help explain the shallow CBL depths at the four sites, while topographically forced low-level convergence helps maintain larger CBL depths at the fifth site near the southern end of the valley. L. Bianco I. Djalalova C. W. King J. M. Wilczak 2016-10-13T18:51:14Z 2016-10-13T18:51:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1396 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1396 2016-10-13T18:51:14Z A Wind Energy Ramp Tool and Metric for Measuring the Skill of Numerical Weather Prediction Models A wind energy Ramp Tool and Metric (RT&M) has been developed out of recognition that during significant ramp events (large changes in wind power over short periods of time ) it is more difficult to balance the electric load with power production than during quiescent periods between ramp events. A ramp-specific metric is needed because standard metrics do not give special consideration to ramp events and hence may not provide an appropriate measure of model skill or skill improvement. This RT&M has three components. The first identifies ramp events in the power time series. The second matches in time forecast and observed ramps. The third determines a skill score of the forecast model. This is calculated from a utility operator's perspective, incorporates phase and duration errors in time as well as power amplitude errors, and recognizes that up and down ramps have different impacts on grid operation. The RT&M integrates skill over a matrix of ramp events of varying amplitudes and durations. L. Bianco I. Djalalova J. M. Wilczak J. Cline S. Calvert E. A. Konopleva C. Finley J. Freedman 2014-07-15T18:26:47Z 2014-07-15T18:26:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1055 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1055 2014-07-15T18:26:47Z Implementation of a Gabor Transform Data Quality-Control Algorithm for UHF Wind Profiling Radars In this paper a Gabor transform–based algorithm is applied to identify and eliminate intermittent signal contamination in UHF wind profiling radars, such as that produced by migrating birds. The algorithm is applied in the time domain, and so it can be used to improve the accuracy of UHF radar wind profiler data in real time—an essential requirement if these wind profiler data are to be assimilated into operational weather forecast models. The added value of using a moment-level Weber–Wuertz pattern recognition scheme that follows the Gabor transform processing is demonstrated. L. Bianco D. J. Gottas J. M. Wilczak 2012-11-09T20:06:59Z 2013-05-08T15:37:00Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/583 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/583 2012-11-09T20:06:59Z Convective Boundary Layer Depth Estimation from Wind Profilers: Statistical Comparison between an Automated Algorithm and Expert Estimations A previous study showed success in determining the convective boundary layer depth with radar wind-profiling radars using fuzzy logic methods, and improvements to the earlier work are discussed. The improved method uses the Vaisala multipeak picking (MPP) procedure to identify the atmospheric signal in radar spectra in place of a fuzzy logic peak picking procedure that was previously used. The method then applies fuzzy logic techniques to calculate the depth of the convective boundary layer. The planetary boundary layer depth algorithm is improved with respect to the one used in the previous study in that it adds information obtained from the small-scale turbulence (vertical profiles of the spectral width of the vertical velocity), while also still using vertical profiles of the radar-derived refractive index structure parameter C2n and the variance of vertical velocity. Modifications to the fuzzy logic rules (especially to those using vertical velocity data) that improve the algorithm's accuracy in cloudy boundary layers are incorporated. In addition, a reliability threshold value to the fuzzy logic–derived score is applied to eliminate PBL depth data values with low score values. These low score values correspond to periods when the PBL structure does not match the conceptual model of the convective PBL built into the algorithm. Also, as a final step, an optional temporal continuity test on boundary layer depth has been developed that helps improve the algorithm's skill. A comparison with independent boundary layer depth estimations made "by eye" by meteorologists at two radar wind-profiler sites, significantly different in their characteristics, shows that the new improved method gives significantly more accurate estimates of the boundary layer depth than does the previous method, and also much better estimates than the simpler "standard" method of selecting the peak of C2n. The new method produces an absolute error of the mixing-depth estimates comparable to the vertical range resolution of the profilers. L. Bianco J. M. Wilczak A. B. White 2012-11-09T20:12:07Z 2013-02-05T21:31:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/584 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/584 2012-11-09T20:12:07Z Aircraft based soil moisture retrievals under mixed vegetation and topographic conditions An unresolved issue in global soil moisture retrieval using passive microwave sensors is the spatial integration of heterogeneous landscape features to the nominal 50 km footprint observed by most low frequency satellite systems. One of the objectives of the Soil Moisture Experiments 2004 (SMEX04) was to address some aspects of this problem, specifically variability introduced by vegetation, topography and convective precipitation. Other goals included supporting the development of soil moisture data sets that would contribute to understanding the role of the land surface in the concurrent North American Monsoon System. SMEX04 was conducted over two regions: Arizona — semi-arid climate with sparse vegetation and moderate topography, and Sonora (Mexico) — moderate vegetation with strong topographic gradients. The Polarimetric Scanning Radiometer (PSR/CX) was flown on a Naval Research Lab P-3B aircraft as part of SMEX04 (10 dates of coverage over Arizona and 11 over Sonora). Radio Frequency Interference (RFI) was observed in both PSR and satellite-based (AMSR-E) observations at 6.92 GHz over Arizona, but no detectable RFI was observed over the Sonora domain. The PSR estimated soil moisture was in agreement with the ground-based estimates of soil moisture over both domains. The estimated error over the Sonora domain (SEE = 0.021 cm3/cm3) was higher than over the Arizona domain (SEE = 0.014 cm3/cm3). These results show the possibility of estimating soil moisture in areas of moderate and heterogeneous vegetation and high topographic variability. R. Bindlish T. J. Jackson A. J. Gasiewski B. B. Stankov et al. 2014-07-15T18:58:49Z 2015-04-30T17:26:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1056 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1056 2014-07-15T18:58:49Z Detection and Attribution of Climate Change: from Global to Regional N/A N. L. Bindoff P. A. Stott . . . J. Perlwitz et al. 2012-09-28T20:54:15Z 2013-05-03T14:51:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/277 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/277 2012-09-28T20:54:15Z The performance of a global and mesoscale model over the central Arctic Ocean during late summer Measurements of turbulent fluxes, clouds, radiation, and profiles of mean meteorological parameters, obtained over an ice floe in the central Arctic Ocean during the Arctic Ocean Experiment 2001, are used to evaluate the performance of U.K. Met Office Unified Model (MetUM) and Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) in the lower atmosphere during late summer. Both the latest version of the MetUM and the version operational in 2001 are used in the comparison to gain an insight as to whether updates to the model have improved its performance over the Arctic region. As with previous model evaluations over the Arctic, the pressure, humidity, and wind fields are satisfactorily represented in all three models. The older version of the MetUM underpredicts the occurrence of low-level Arctic clouds, and the liquid and ice cloud water partitioning is inaccurate compared to observations made during SHEBA. In the newer version, simulated ice and liquid water paths are improved, but the occurrence of low-level clouds are overpredicted. Both versions overestimate the amount of radiative heat absorbed at the surface, leading to a significant feedback of errors involving the surface albedo, which causes a large positive bias the surface temperature. Cloud forcing in COAMPS produces similar biases in the downwelling shortwave and longwave radiation fluxes to those produced by UM(G25). The surface albedo parameterization is, however, more realistic, and thus, the total heat flux and surface temperature are more accurate for the majority of the observation period. C. E. Birch I. M. Brooks M. Tjernström S. F. Milton P. Earnshaw S. Söderberg P. O. G. Persson 2012-09-20T21:03:58Z 2013-05-06T16:03:50Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/99 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/99 2012-09-20T21:03:58Z Modelling atmospheric structure, cloud and their responses to CCN in the central Arctic: ASCOS case studies Observations made during late summer in the central Arctic Ocean, as part of the Arctic Summer Cloud Ocean Study (ASCOS), are used to evaluate cloud and vertical temperature structure in the Met Office Unified Model (MetUM). The observation period can be split into 5 regimes; the first two regimes had a large number of frontal systems, which were associated with deep cloud. During the remainder of the campaign a layer of low-level cloud occurred, typical of central Arctic summer conditions, along with two periods of greatly reduced cloud cover. The short-range operational NWP forecasts could not accurately reproduce the observed variations in near-surface temperature. A major source of this error was found to be the temperature-dependant surface albedo parameterisation scheme. The model reproduced the low-level cloud layer, though it was too thin, too shallow, and in a boundary-layer that was too frequently well-mixed. The model was also unable to reproduce the observed periods of reduced cloud cover, which were associated with very low cloud condensation nuclei (CCN) concentrations (<1 cm−3). As with most global NWP models, the MetUM does not have a prognostic aerosol/cloud scheme but uses a constant CCN concentration of 100 cm−3 over all marine environments. It is therefore unable to represent the low CCN number concentrations and the rapid variations in concentration frequently observed in the central Arctic during late summer. Experiments with a single-column model configuration of the MetUM show that reducing model CCN number concentrations to observed values reduces the amount of cloud, increases the near-surface stability, and improves the representation of both the surface radiation fluxes and the surface temperature. The model is shown to be sensitive to CCN only when number concentrations are less than 10–20 cm−3. C. E. Birch I. M. Brooks M. Tjernström M. D. Shupe T. Mauritsen J. Sedlar A. P. Lock P. Earnshaw P. O. G. Persson S. F. Milton C. Leck 2016-04-11T20:57:43Z 2016-04-11T20:59:08Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1312 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1312 2016-04-11T20:57:43Z Scenarios for vulnerability: opportunities and constraints in the context of climate change and disaster risk Most scientific assessments for climate change adaptation and risk reduction are based on scenarios for climatic change. Scenarios for socio-economic development, particularly in terms of vulnerability and adaptive capacity, are largely lacking. This paper focuses on the utility of socio-economic scenarios for vulnerability, risk and adaptation research. The paper introduces the goals and functions of scenarios in general and reflects on the current global debate around shared socio-economic pathways (SSPs). It examines the options and constraints of scenario methods for risk and vulnerability assessments in the context of climate change and natural hazards. Two case studies are used to contrast the opportunities and current constraints in scenario methods at different scales: the global WorldRiskIndex, based on quantitative data and indicators; and a local participatory scenario development process in Jakarta, showing a qualitative approach. The juxtaposition of a quantitative approach with global data and a qualitative-participatory local approach provides new insights on how different methods and scenario techniques can be applied in vulnerability and risk research. J. Birkmann S. L. cutter D. S. Rothman . . . R. S. Pulwarty 2012-09-21T23:46:41Z 2014-01-08T21:03:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/106 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/106 2012-09-21T23:46:41Z Rates of thermohaline recovery from freshwater pulses in Modern, Last Glacial Maximum and Greenhouse Warming Climates Recovery rates of the thermohaline circulation after a freshwater pulse in the North Atlantic vary considerably depending on the background climate, as demonstrated in the Community Climate System Model. The recovery is slowest in a Last Glacial Maximum (LGM) climate, fastest in a modern climate, and intermediate between the two in a greenhouse warming (4XCO2) climate. Previously proposed mechanisms to explain thermohaline circulation stability involving altered horizontal freshwater transport in the North Atlantic are consistent with relative recovery rates in the modern and 4XCO2 climates, but fail to explain the slow LGM recovery. Instead, sea ice expansion inhibits deep-water formation after freshening in the LGM climate by reducing heat loss to the atmosphere and providing additional surface freshwater. In addition, anomalous vertical freshwater transport across ∼1 km depth after freshening is most effective at weakening the stratification in the modern case but is negligible in the LGM case. C. M. Bitz J. C. H. Chiang W. Cheng J. J. Barsugli 2012-10-15T23:44:29Z 2013-05-07T17:25:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/293 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/293 2012-10-15T23:44:29Z Air–Sea Exchange in Hurricanes: Synthesis of Observations from the Coupled Boundary Layer Air–Sea Transfer Experiment The Coupled Boundary Layer Air–Sea Transfer (CBLAST) field program, conducted from 2002 to 2004, has provided a wealth of new air–sea interaction observations in hurricanes. The wind speed range for which turbulent momentum and moisture exchange coefficients have been derived based upon direct f lux measurements has been extended by 30% and 60%, respectively, from airborne observations in Hurricanes Fabian and Isabel in 2003. The drag coefficient (CD) values derived from CBLAST momentum flux measurements show CD becoming invariant with wind speed near a 23 m s−1 threshold rather than a hurricane-force threshold near 33 m s−1. Values above 23 m s−1 are lower than previous open-ocean measurements. The Dalton number estimates (CE) derived from CBLAST moisture flux measurements are shown to be invariant with wind speeds up to 30 m s−1, which is in approximate agreement with previous measurements at lower winds. These observations imply a CE/CD ratio of approximately 0.7, suggesting that additional energy sources are necessary for hurricanes to achieve their maximum potential intensity. One such additional mechanism for augmented moisture flux in the boundary layer might be "roll vortex" or linear coherent features, observed by CBLAST 2002 measurements to have wavelengths of 0.9–1.2 km. Linear features of the same wavelength range were observed in nearly concurrent RADARSAT Synthetic Aperture Radar (SAR) imagery. As a complement to the aircraft measurement program, arrays of drifting buoys and subsurface floats were successfully deployed ahead of Hurricanes Fabian (2003) and Frances (2004) [16 (6) and 38 (14) drifters (floats), respectively, in the two storms]. An unprecedented set of observations was obtained, providing a four-dimensional view of the ocean response to a hurricane for the first time ever. Two types of surface drifters and three types of floats provided observations of surface and sub-surface oceanic currents, temperature, salinity, gas exchange, bubble concentrations, and surface wave spectra to a depth of 200 m on a continuous basis before, during, and after storm passage, as well as surface atmospheric observations of wind speed (via acoustic hydrophone) and direction, rain rate, and pressure. Float observations in Frances (2004) indicated a deepening of the mixed layer from 40 to 120 m in approximately 8 h, with a corresponding decrease in SST in the right-rear quadrant of 3.2°C in 11 h, roughly one-third of an inertial period. Strong inertial currents with a peak amplitude of 1.5 m s−1 were observed. Vertical structure showed that the critical Richardson number was reached sporadically during the mixed-layer deepening event, suggesting shear-induced mixing as a prominent mechanism during storm passage. Peak significant waves of 11 m were observed from the floats to complement the aircraft-measured directional wave spectra. P. G. Black E. A. D'Asaro W. M. Drennan J. R. French P. P. Niiler T. B. Sanford E. J. Terrill E. J. Walsh J. A. Zhang 2012-12-21T20:25:14Z 2013-05-06T16:34:57Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/843 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/843 2012-12-21T20:25:14Z The summer North Atlantic Oscillation in CMIP3 models and related uncertainties in projected summer drying in Europe This paper discusses uncertainties in model projections of summer drying in the Euro-Mediterranean region related to errors and uncertainties in the simulation of the summer NAO (SNAO). The SNAO is the leading mode of summer SLP variability in the North Atlantic/European sector and modulates precipitation not only in the vicinity of the SLP dipole (northwest Europe) but also in the Mediterranean region. An analysis of CMIP3 models is conducted to determine the extent to which models reproduce the signature of the SNAO and its impact on precipitation and to assess the role of the SNAO in the projected precipitation reductions. Most models correctly simulate the spatial pattern of the SNAO and the dry anomalies in northwest Europe that accompany the positive phase. The models also capture the concurrent wet conditions in the Mediterranean, but the amplitude of this signal is too weak, especially in the east. This error is related to the poor simulation of the upper-level circulation response to a positive SNAO, namely the observed trough over the Balkans that creates potential instability and favors precipitation. The SNAO is generally projected to trend upwards in CMIP3 models, leading to a consistent signal of precipitation reduction in NW Europe, but the intensity of the trend varies greatly across models, resulting in large uncertainties in the magnitude of the projected drying. In the Mediterranean, because the simulated influence of the SNAO is too weak, no precipitation increase occurs even in the presence of a strong SNAO trend, reducing confidence in these projections. I. Bladé D. Fortuny G. J. van Oldenborgh B. Liebmann 2012-11-09T23:07:05Z 2013-05-06T16:10:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/603 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/603 2012-11-09T23:07:05Z Observed and simulated impacts of the summer NAO in Europe: implications for projected drying in the Mediterranean region Climate models predict substantial summer precipitation reductions in Europe and the Mediterranean region in the twenty-first century, but the extent to which these models correctly represent the mechanisms of summertime precipitation in this region is uncertain. Here an analysis is conducted to compare the observed and simulated impacts of the dominant large-scale driver of summer rainfall variability in Europe and the Mediterranean, the summer North Atlantic Oscillation (SNAO). The SNAO is defined as the leading mode of July–August sea level pressure variability in the North Atlantic sector. Although the SNAO is weaker and confined to northern latitudes compared to its winter counterpart, with a southern lobe located over the UK, it significantly affects precipitation in the Mediterranean, particularly Italy and the Balkans (correlations of up to 0.6). During high SNAO summers, when strong anticyclonic conditions and suppressed precipitation prevail over the UK, the Mediterranean region instead is anomalously wet. This enhanced precipitation is related to the presence of a strong upper-level trough over the Balkans—part of a hemispheric pattern of anomalies that develops in association with the SNAO—that leads to mid-level cooling and increased potential instability. Neither this downstream extension nor the surface influence of the SNAO is captured in the two CMIP3 models examined (HadCM3 and GFDL-CM2.1), with weak or non-existent correlations between the SNAO and Mediterranean precipitation. Because these models also predict a strong upward SNAO trend in the future, the error in their representation of the SNAO surface signature impacts the projected precipitation trends. In particular, the attendant increase in precipitation that, based on observations, should occur in the Mediterranean and offset some of the non-SNAO related drying does not occur. Furthermore, the fact that neither the observed SNAO nor summer precipitation in Europe/Mediterranean region exhibits any significant trend so far (for either the full century or the recent half of the record) does not increase our confidence in these model projections. I. Bladé B. Liebmann D. Fortuny G. J. van Oldenborgh 2012-11-09T20:16:02Z 2013-05-08T15:37:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/585 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/585 2012-11-09T20:16:02Z The Late Fall Extratropical Response to ENSO: Sensitivity to Coupling and Convection in the Tropical West Pacific The extratropical response to El Niño in late fall departs considerably from the canonical El Niño signal. Observational analysis suggests that this response is modulated by anomalous forcing in the tropical west Pacific (TWP), so that a strong fall El Niño teleconnection is more likely when warm SST conditions and/or enhanced convection prevail in the TWP. While these TWP SST anomalies may arise from noise and/or long-term variability, they may also be generated by differences between El Niño events, through variations in the tropical "atmospheric bridge." This bridge typically drives subsidence west of the date line and enhanced trade winds over the far TWP, which cool the ocean. In late fall, however, some relatively weaker and/or more eastward-shifted El Niño events produce a correspondingly weakened and displaced tropical bridge, which results in no surface cooling and enhanced convection in the TWP. Because the North Pacific circulation is very sensitive to forcing from the TWP at this time of year, the final outcome is a strong extratropical El Niño teleconnection. This hypothesis is partly supported by regionally coupled ensemble GCM simulations for the 1950–99 period, in which prescribed observed El Niño SST anomalies in the eastern/central equatorial Pacific and an oceanic mixed layer model elsewhere coexist, so that the TWP is allowed to interact with the El Niño atmospheric bridge. To separate the deterministic signal driven by TWP coupling from that associated with inter–El Niño differences and from the "noise" due to intrinsic TWP convection variability (not induced by local SST anomalies), a second large-ensemble (100) simulation of the 1997/98 El Niño event, with coupling limited to the TWP and tropical Indian Ocean, is carried out. Together, the model findings suggest that the extratropical El Niño teleconnection during late fall is very sensitive to convective forcing in the TWP and that coupling-induced warming in the TWP may enhance this El Niño teleconnection by promoting convection in this critical TWP region. A more general implication is that diagnostic studies using December–February (DJF) seasonal averages may obscure some important aspects of climate anomalies associated with forcing in the tropical Pacific. I. Bladé M. Newman M. A. Alexander J. D. Scott 2015-04-24T17:23:50Z 2015-10-06T22:30:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1146 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1146 2015-04-24T17:23:50Z Synergistic Analysis of Cloud Cover and Vertical Distribution from A-Train and Ground-Based Sensors over the High Arctic Station Eureka from 2006 to 2010 Active remote sensing instruments such as lidar and radar allow one to accurately detect the presence of clouds and give information on their vertical structure and phase. To better address cloud radiative impact over the Arctic area, a combined analysis based on lidar and radar ground-based and A-Train satellite measurements was carried out to evaluate the efficiency of cloud detection, as well as cloud type and vertical distribution, over the Eureka station (80°N, 86°W) between June 2006 and May 2010. Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat data were first compared with independent ground-based cloud measurements. Seasonal and monthly trends from independent observations were found to be similar among all datasets except when compared with the weather station observations because of the large reported fraction of ice crystals suspended in the lower troposphere in winter. Further investigations focused on satellite observations that are collocated in space and time with ground-based data. Cloud fraction occurrences from ground-based instruments correlated well with both CALIPSO operational products and combined CALIPSO–CloudSat retrievals, with a hit rate of 85%. The hit rate was only 77% for CloudSat products. The misdetections were mainly attributed to 1) undetected low-level clouds as a result of sensitivity loss and 2) missed clouds because of the distance between the satellite track and the station. The spaceborne lidar–radar synergy was found to be essential to have a complete picture of the cloud vertical profile down to 2 km. Errors are quantified and discussed. Y. Blanchard J. Pelon E. W. Eloranta K. P. Moran J. Delanoë G. Sèze 2015-10-07T14:35:17Z 2015-10-07T14:35:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1221 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1221 2015-10-07T14:35:17Z A Vertically Flow-Following Icosahedral Grid Model for Medium-Range and Seasonal Prediction. Part I: Model Description A hydrostatic global weather prediction model based on an icosahedral horizontal grid and a hybrid terrain-following/isentropic vertical coordinate is described. The model is an extension to three spatial dimensions of a previously developed, icosahedral, shallow-water model featuring user-selectable horizontal resolution and employing indirect addressing techniques. The vertical grid is adaptive to maximize the portion of the atmosphere mapped into the isentropic coordinate subdomain. The model, best described as a stacked shallow-water model, is being tested extensively on real-time medium-range forecasts to ready it for possible inclusion in operational multimodel ensembles for medium-range to seasonal prediction. R. Bleck J.-W. Bao S. G. Benjamin . . . 2012-09-21T23:52:55Z 2013-05-15T16:11:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/107 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/107 2012-09-21T23:52:55Z Soil moisture mapping and AMSR-E validation using the PSR in SMEX02 Field experiments (SMEX02) were conducted to evaluate the effects of dense agricultural crop conditions on soil moisture retrieval using passive microwave remote sensing. Aircraft observations were collected using a new version of the Polarimetric Scanning Radiometer (PSR) that provided four C band and four X band frequencies. Observations were also available from the Aqua satellite Advanced Microwave Scanning Radiometer (AMSR-E) at these same frequencies. SMEX02 was conducted over a three-week period during the summer near Ames, Iowa. Corn and soybeans dominate the region. During the study period the corn was approaching its peak water content state and the soybeans were at the mid point of the growth cycle. Aircraft observations are compared to ground observations. Subsequently models are developed to describe the effects of corn and soybeans on soil moisture retrieval. Multiple altitude aircraft brightness temperatures were compared to AMSR-E observations to understand brightness temperature scaling and provide validation. The X-band observations from the two sensors were in reasonable agreement. The AMSR-E C-band observations were contaminated with anthropogenic RFI, which made comparison to the PSR invalid. Aircraft data along with ancillary data were used in a retrieval algorithm to map soil moisture. The PSR estimated soil moisture retrievals on a field-by-field comparison had a standard error of estimate (SEE) of 5.5%. The error reduced when high altitude soil moisture estimates were aggregated to 25 km resolution (same as AMSR-E EASE grid product resolution) (SEE ∼ 2.85%). These soil moisture products provide a validation of the AMSR retrievals. PSR/CX soil moisture images show spatial and temporal patterns consistent with meteorological and soil conditions. The dynamic range of the PSR/CX observations indicates that reasonable soil moisture estimates can be obtained from AMSR, even in areas of high vegetation biomass content (∼ 4–8 kg/m2). R. Blindish T. J. Jackson A. J. Gasiewski M. Klein E. G. Njoku 2012-09-21T23:57:27Z 2013-05-13T15:18:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/108 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/108 2012-09-21T23:57:27Z DMS sea-air transfer velocity. Direct measurements by eddy covariance and parameterization based on the NOAA/COARE gas transfer model Estimates of the DMS sea-air transfer velocity (kDMS) derived from direct flux measurements are poorly modeled by parameterizations based solely on wind speed and Schmidt number. DMS and CO2 flux measurements show to be a stronger function of wind speed than kDMS. The NOAA/COARE gas flux parameterization, incorporating the bubble-mediated gas transfer theory of Woolf (1997), appears to do a better job reproducing the observations for both gases, illustrating the importance of trace gas solubility in sea-air exchange. The development of gas transfer parameterizations based on physical principles is still in its infancy, but recent advances in direct flux measurement methods provide an opportunity to evaluate the success of various modeling approaches for this critical geophysical process. B. W. Blomquist C. W. Fairall B. J. Huebert D. J. Kieber G. R. Westby 2013-01-31T21:32:59Z 2013-04-24T17:41:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/881 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/881 2013-01-31T21:32:59Z Direct measurement of the oceanic carbon monoxide flux by eddy correlation This report presents results from a field trial of ship-based air–sea flux measurements of carbon monoxide (CO) by direct eddy correlation with an infrared-laser trace gas analyzer. The analyzer utilizes Off-Axis Integrated-Cavity-Output Spectroscopy (OA-ICOS) to achieve high selectivity for CO, rapid response (~2 Hz) and low noise. Over a two-day sea trial, peak daytime seawater CO concentrations were ~1.5 nM and wind speeds were consistently 10–12 m s−1. A clear diel cycle in CO flux with an early afternoon maximum was observed. An analysis of flux error suggests the effects of non-stationarity are important, and air–sea CO flux measurements are best performed in regions remote from continental pollution sources. B. W. Blomquist C. W. Fairall B. J. Huebert S. T. Wilson 2012-09-25T21:33:17Z 2013-05-08T14:54:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/212 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/212 2012-09-25T21:33:17Z Determining the sea-air flux of dimethylsulfide by eddy correlation using mass spectrometry Mass spectrometric measurement of DMS by atmospheric pressure ionization with an isotopically labeled standard (APIMS-ILS) is a sensitive method with sufficient bandpass for direct flux measurements by eddy correlation. Use of an isotopically labeled internal standard greatly reduces instrumental drift, improving accuracy and precision. APIMS-ILS has been used in several recent campaigns to study ocean-atmosphere gas transfer and the chemical budget of DMS in the marine boundary layer. This paper provides a comprehensive description of the method and errors associated with DMS flux measurement from ship platforms. The APIMS-ILS instrument used by most groups today has a sensitivity of 100–200 counts s−1 pptv−1, which is shown to be more than sufficient for flux measurement by eddy covariance. Mass spectral backgrounds (blanks) are determined by stripping DMS from ambient air with gold. The instrument is found to exhibit some high frequency signal loss, with a half-power frequency of ≈1 Hz, but a correction based on an empirically determined instrument response function is presented. Standard micrometeorological assumptions of steady state and horizontal uniformity are found to be appropriate for DMS flux measurement, but rapid changes in mean DMS mixing ratio may serve as a warning that measured flux does not represent the true surface flux. In addition, bias in surface flux estimates arising from the flux divergence is not generally significant in the surface layer, but under conditions of lowered inversion and high flux may become so. The effects of error in motion corrections and of vertical motion within the surface layer concentration gradient are discussed and the estimated maximum error from these effects is ≤18%. B. W. Blomquist B. J. Huebert C. W. Fairall I. C. Faloona 2015-04-20T20:58:40Z 2015-04-29T16:06:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1122 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1122 2015-04-20T20:58:40Z Advances in Air–Sea CO2 Flux Measurement by Eddy Correlation Eddy-correlation measurements of the oceanic CO2 flux are useful for the development and validation of air–sea gas exchange models and for analysis of the marine carbon cycle. Results from more than a decade of published work and from two recent field programs illustrate the principal interferences from water vapour and motion, demonstrating experimental approaches for improving measurement precision and accuracy. Water vapour cross-sensitivity is the greatest source of error for CO2 flux measurements using infrared gas analyzers, often leading to a ten-fold bias in the measured CO2 flux. Much of this error is not related to optical contamination, as previously supposed. While various correction schemes have been demonstrated, the use of an air dryer and closed-path analyzer is the most effective way to eliminate this interference. This approach also obviates density corrections described by Webb et al. (Q J R Meteorol 106:85–100, 1980). Signal lag and frequency response are a concern with closed-path systems, but periodic gas pulses at the inlet tip provide for precise determination of lag time and frequency attenuation. Flux attenuation corrections are shown to be <5 % for a cavity ring-down analyzer (CRDS) and dryer with a 60-m inlet line. The estimated flux detection limit for the CRDS analyzer and dryer is a factor of ten better than for IRGAs sampling moist air. While ship-motion interference is apparent with all analyzers tested in this study, decorrelation or regression methods are effective in removing most of this bias from IRGA measurements and may also be applicable to the CRDS. B. W. Blomquist B. J. Huebert C. W. Fairall L. Bariteau J. B. Edson J. E. Hare W. R. McGillis 2012-05-04T16:36:21Z 2013-05-02T16:10:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/24 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/24 2012-05-04T16:36:21Z Evaluation of the flux gradient technique for measurement of ozone surface fluxes over snowpack at Summit, Greenland. A multi-step procedure for investigating ozone surface fluxes over polar snow by the tower gradient method was developed and evaluated. These measurements were then used to obtain five months (April–August 2004) of turbulent ozone flux data at the Summit research camp located in the center of the Greenland ice shield. Turbulent fluxes were determined by the gradient method incorporating tower measurements of (a) ozone gradients measured by commercial ultraviolet absorption analyzers, (b) ambient temperature gradients using aspirated thermocouple sensors, and (c) wind speed gradients determined by cup anemometers. All gradient instruments were regularly inter-compared by bringing sensors or inlets to the same measurement height. The developed protocol resulted in an uncertainty on the order of 0.1 ppbv for 30-min averaged ozone gradients that were used for the ozone flux calculations. This protocol facilitated a lower sensitivity threshold for the ozone flux determination of ∼8 × 10−3μg m−2 s−1, respectively ∼0.01 cm s−1 for the ozone deposition velocity for typical environmental conditions encountered at Summit. Uncertainty in the 30-min ozone exchange measurements (evaluated by the Monte Carlo statistical approach) was on the order of 10−2 cm s−1. This uncertainty typically accounted to ~20–100% of the ozone exchange velocities that were determined. These measurements are among the most sensitive ozone deposition determinations reported to date. This flux experiment allowed for measurements of the relatively low ozone uptake rates encountered for polar snow, and thereby the study of their environmental and spring-versus-summer dependencies. F. Bocquet D. Helmig B. Van Dam C. W. Fairall 2012-11-13T17:15:58Z 2013-05-02T16:27:00Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/614 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/614 2012-11-13T17:15:58Z COSP: Satellite simulation software for model assessment Errors in the simulation of clouds in general circulation models (GCMs) remain a long-standing issue in climate projections, as discussed in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report. This highlights the need for developing new analysis techniques to improve our knowledge of the physical processes at the root of these errors. The Cloud Feedback Model Intercomparison Project (CFMIP) pursues this objective, and under that framework the CFMIP Observation Simulator Package (COSP) has been developed. COSP is a flexible software tool that enables the simulation of several satellite-borne active and passive sensor observations from model variables. The flexibility of COSP and a common interface for all sensors facilitates its use in any type of numerical model, from high-resolution cloud-resolving models to the coarser-resolution GCMs assessed by the IPCC, and the scales in between used in weather forecast and regional models. The diversity of model parameterization techniques makes the comparison between model and observations difficult, as some parameterized variables (e.g., cloud fraction) do not have the same meaning in all models. The approach followed in COSP permits models to be evaluated against observations and compared against each other in a more consistent manner. This permits a more detailed diagnosis of the physical processes that govern the behavior of clouds and precipitation in numerical models. The World Climate Research Programme (WCRP) Working Group on Coupled Modelling has recommended the use of COSP in a subset of climate experiments that will be assessed by the next IPCC report. In this article we describe COSP, present some results from its application to numerical models, and discuss future work that will expand its capabilities. A. Bodas-Salcedo M. J. Webb S. Bony . . . R. Pincus et al. 2014-01-09T00:44:01Z 2014-01-09T00:44:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1008 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1008 2014-01-09T00:44:01Z Global evaluation of MTCLIM and related algorithms for forcing of ecological and hydrological models We assessed the performance of the MTCLIM scheme for estimating downward shortwave (SWdown) radiation and surface humidity from daily temperature range (DTR), as well as several schemes for estimating downward longwave radiation (LWdown), at 50 Baseline Solar Radiation Network stations globally. All of the algorithms performed reasonably well under most climate conditions, with biases and mean absolute errors generally less than 3% and 20%, respectively, over more than 70% of the global land surface. However, estimated SWdown had a bias of −26% at coastal sites, due to the ocean's moderating influence on DTR, and in continental interiors, SWdown had an average bias of −15% in the presence of snow, which was reduced by MTCLIM 4.3's snow correction if local topography was taken into account. Vapor pressure (VP) and relative humidity (RH) had large negative biases (up to −50%) under the most arid conditions. At coastal sites, LWdown had positive biases of up to 10%, while biases at interior sites exhibited a weak dependence on DTR. The largest biases in both RH (negative) and LWdown (positive) were concentrated over the world's deserts, while smaller positive humidity biases were found over tropical and boreal forests. Evaluation of the diurnal cycle showed negative morning, and positive afternoon biases in vapor pressure deficit and LWdown related to errors in the interpolation of the diurnal air temperature. T. J. Bohn B. Livneh J. W. Oyler S. W. Running B. Nijssen D. Lettenmaier 2016-04-11T21:03:29Z 2016-04-11T21:03:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1313 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1313 2016-04-11T21:03:29Z Relative Contributions of Mean-State Shifts and ENSO-Driven Variability to Precipitation Changes in a Warming Climate El Niño–Southern Oscillation (ENSO) is an important driver of regional hydroclimate variability through far-reaching teleconnections. This study uses simulations performed with coupled general circulation models (CGCMs) to investigate how regional precipitation in the twenty-first century may be affected by changes in both ENSO-driven precipitation variability and slowly evolving mean rainfall. First, a dominant, time-invariant pattern of canonical ENSO variability (cENSO) is identified in observed SST data. Next, the fidelity with which 33 state-of-the-art CGCMs represent the spatial structure and temporal variability of this pattern (as well as its associated precipitation responses) is evaluated in simulations of twentieth-century climate change. Possible changes in both the temporal variability of this pattern and its associated precipitation teleconnections are investigated in twenty-first-century climate projections. Models with better representation of the observed structure of the cENSO pattern produce winter rainfall teleconnection patterns that are in better accord with twentieth-century observations and more stationary during the twenty-first century. Finally, the model-predicted twenty-first-century rainfall response to cENSO is decomposed into the sum of three terms: 1) the twenty-first-century change in the mean state of precipitation, 2) the historical precipitation response to the cENSO pattern, and 3) a future enhancement in the rainfall response to cENSO, which amplifies rainfall extremes. By examining the three terms jointly, this conceptual framework allows the identification of regions likely to experience future rainfall anomalies that are without precedent in the current climate. C. J. W. Bonfils B. D. Santer T. J. Phillips K. Marvel L. R. Leung C. Doutriaux A. Capotondi 2015-04-24T19:57:26Z 2015-10-06T22:56:15Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1147 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1147 2015-04-24T19:57:26Z Clouds, circulation and climate sensitivity Fundamental puzzles of climate science remain unsolved because of our limited understanding of how clouds, circulation and climate interact. One example is our inability to provide robust assessments of future global and regional climate changes. However, ongoing advances in our capacity to observe, simulate and conceptualize the climate system now make it possible to fill gaps in our knowledge. We argue that progress can be accelerated by focusing research on a handful of important scientific questions that have become tractable as a result of recent advances. We propose four such questions below; they involve understanding the role of cloud feedbacks and convective organization in climate, and the factors that control the position, the strength and the variability of the tropical rain belts and the extratropical storm tracks. S. Bony B. Stevens . . . R. Pincus et al. 2012-11-08T17:11:56Z 2013-05-06T16:04:40Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/561 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/561 2012-11-08T17:11:56Z An Analysis of Multiple Predecessor Rain Events ahead of Tropical Cyclones Ike and Lowell: 10–15 September 2008 An analysis of three predecessor rain events (PREs) that occurred ahead of North Atlantic tropical cyclone (TC) Ike and east Pacific TC Lowell during 10–15 September 2008 is presented. The three PREs produced all-time daily record rainfall at many locations, including Lubbock, Texas (189.5 mm); Wichita, Kansas (262 mm); and Chicago–O'Hare, Illinois (169 mm), on 11–13 September, respectively. PRE 1 organized over Texas on 10 September with moisture from a stalled frontal boundary and the Bay of Campeche, and matured with moisture from TC Lowell. PRE 2 organized over the Texas Panhandle on 11 September with moisture from the Bay of Campeche, and developed and matured over Kansas and Missouri with moisture from TC Lowell. PRE 3 developed over Texas on 11 September, merged with and absorbed PRE 2 over Kansas and Missouri, and matured as it ingested moisture from TC Ike. All three PREs matured in the equatorward entrance region of an intensifying subtropical jet stream (STJ). Heavy rainfall with the three PREs occurred along a plume of moist air characterized by high precipitable water values that extended poleward over the central United States near the juxtaposition of the nose of a low-level jet, a region of lower-tropospheric forcing for ascent along a surface baroclinic zone, and the STJ equatorward entrance region. The cumulative upscale effect of persistent deep convection from the three PREs enhanced and "locked in" a favorable upper-tropospheric flow pattern conducive to ridge development over the Ohio Valley and STJ intensification over the central U.S. and Great Lakes region. L. F. Bosart J. M. Cordeira T. J. Galarneau B. J. Moore H. M. Archambault 2012-09-25T21:45:50Z 2013-05-08T15:02:19Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/213 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/213 2012-09-25T21:45:50Z The THORPEX interactive grand global ensemble Ensemble forecasting is increasingly accepted as a powerful tool to improve early warnings for high-impact weather. Recently, ensembles combining forecasts from different systems have attracted a considerable level of interest. The Observing System Research and Predictability Experiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) project, a prominent contribution to THORPEX, has been initiated to enable advanced research and demonstration of the multimodel ensemble concept and to pave the way toward operational implementation of such a system at the international level. The objectives of TIGGE are 1) to facilitate closer cooperation between the academic and operational meteorological communities by expanding the availability of operational products for research, and 2) to facilitate exploring the concept and benefits of multimodel probabilistic weather forecasts, with a particular focus on high-impact weather prediction. Ten operational weather forecasting centers producing daily global ensemble forecasts to 1–2 weeks ahead have agreed to deliver in near–real time a selection of forecast data to the TIGGE data archives at the China Meteorological Agency, the European Centre for Medium-Range Weather Forecasts, and the National Center for Atmospheric Research. The volume of data accumulated daily is 245 GB (1.6 million global fields). This is offered to the scientific community as a new resource for research and education. The TIGGE data policy is to make each forecast accessible via the Internet 48 h after it was initially issued by each originating center. Quicker access can also be granted for field experiments or projects of particular interest to the World Weather Research Programme and THORPEX. A few examples of initial results based on TIGGE data are discussed in this paper, and the case is made for additional research in several directions. P. Bougeault Z. Toth C. Bishop B. Brown D. Burridge D.H. Chen B. Ebert M. Fuentes T. M. Hamill K. Mylne J. Nicolau T. Paccagnella Y.Y. Park D. Parsons B. Raoult D. Schuster P.S. Dias R. Swinbank Y. Takeuchi W. Tennant L. Wilson S. Worley 2013-04-12T22:36:12Z 2013-04-24T17:26:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/902 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/902 2013-04-12T22:36:12Z High-Latitude Ocean and Sea Ice Surface Fluxes: Challenges for Climate Research Polar regions have great sensitivity to climate forcing; however, understanding of the physical processes coupling the atmosphere and ocean in these regions is relatively poor. Improving our knowledge of high-latitude surface fluxes will require close collaboration among meteorologists, oceanographers, ice physicists, and climatologists, and between observationalists and modelers, as well as new combinations of in situ measurements and satellite remote sensing. This article describes the deficiencies in our current state of knowledge about air–sea surface fluxes in high latitudes, the sensitivity of various high-latitude processes to changes in surface fluxes, and the scientific requirements for surface fluxes at high latitudes. We inventory the reasons, both logistical and physical, why existing flux products do not meet these requirements. Capturing an annual cycle in fluxes requires that instruments function through long periods of cold polar darkness, often far from support services, in situations subject to icing and extreme wave conditions. Furthermore, frequent cloud cover at high latitudes restricts the availability of surface and atmospheric data from visible and infrared (IR) wavelength satellite sensors. Recommendations are made for improving high-latitude fluxes, including 1) acquiring more in situ observations, 2) developing improved satellite-flux-observing capabilities, 3) making observations and flux products more accessible, and 4) encouraging flux intercomparisons. M. A. Bourassa S. T. Gille C. M. Bitz . . . C. W. Fairall . . . G. A. Wick 2012-11-15T16:46:29Z 2013-05-07T20:01:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/759 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/759 2012-11-15T16:46:29Z Ocean Winds and Turbulent Air-Sea Fluxes Inferred From Remote Sensing Surface turbulent fluxes are key pathways through which the atmosphere is coupled with the ocean. They provide mechanisms through which momentum, energy, moisture, and materials such as CO2 are transferred between the ocean and atmosphere. Surface fluxes are also important players in vertical and horizontal transport in the atmosphere and the ocean. There have been attempts to estimate surface fluxes directly from satellite observations; however, they are typically calculated from observations of surface and near‑surface variables. Recent improvements in the measurement of vector winds, air temperatures, and atmospheric humidities have all contributed to better estimation of surface fluxes from satellite observations. These advances are discussed in the context of applications, with examples from a tropical cyclone and a very strong mid-latitude storm. Proposed future systems that use improved instrumentation and collocate observations of winds, temperatures, and humidities will increase the accuracy beyond current capabilities. Targets for a variety of important climate-related processes are provided. M. A. Bourassa S. T. Gille D. L. Jackson J. B. Roberts G. A. Wick 2014-07-15T19:02:30Z 2014-07-15T19:02:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1057 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1057 2014-07-15T19:02:30Z Boundary layer dynamics during the Ocean-Atmosphere-Sea-Ice-Snow (OASIS) 2009 experiment at Barrow, AK Three-dimensional atmospheric turbulence measurements were conducted from seven sonic anemometers on two different towers in Barrow, AK, during the spring of 2009 as part of the Ocean-Atmosphere-Sea-Ice-Snow (OASIS) campaign. This was the largest number of side-by-side atmospheric turbulence measurements in the Arctic at one time. These analyses allowed for (1) a comparison of the instrumental measurement approaches and (2) a comparison of the variability of the lower atmospheric surface layer at these measurement heights and tower sites. Friction velocity estimates were affected for a sonic anemometer that was operated on the tower in the near vicinity of a building module. Boundary layer height (BLH) was estimated from sonic anemometer measurements based both on a turbulence variable estimator and a temperature gradient method. Results from both methods were compared to radiosonde-estimated BLH and generally underestimated the BLH for shallower depths. Conditions with low BLH (< 100 m) often lasted for several days. The seven ozone depletion events (ODE) that were observed during the OASIS campaign had a tendency of coinciding with BLH of less than 50 m and stable atmospheric conditions; however, there was not a clear relationship between the occurrence of ODE and wind speed or wind direction as ODE occurred under a wide range of conditions of BLH, wind speed, local wind direction, and atmospheric stability. Comparisons of these surface layer dynamics to sites in Antarctica and Greenland reveal that boundary layer dynamics are not the primary driving force that fosters the unique ozone chemistry at this coastal Arctic site. P. Boylan D. Helmig R. Staebler A. Turnipseed C. W. Fairall W. D. Neff 2015-04-24T19:19:08Z 2015-10-06T23:06:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1148 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1148 2015-04-24T19:19:08Z Impact of a spectral sampling technique for radiation on ECMWF weather forecasts Radiation transfer computations are one of the most expensive components of atmospheric models integrations. Methods generally applied to reduce their computational cost, include less frequent update of the radiative fluxes or coarser spatial grids than those used for the rest of the model. In the operational configuration of the Integrated Forecast System (IFS) used at the European Centre for Medium Range Weather Forecasts (ECMWF), radiation accounts for ∼ 10% of the total computer time, and the radiative fluxes are computed with both a reduced temporal and spatial resolution. In this study, we show that these approximations have a negligible impact on the forecast errors when looking at the large-scale circulation but they lead to biases in the surface temperature. These are linked to inconsistencies in the representation of surface properties or to poorly sampled temporal evolution of the radiative fluxes. Here we explore an alternative method to alleviate such errors, based on a recently developed technique that estimates radiative fluxes from randomly-chosen subsets of spectral points designed to minimize the surface flux error. This approach introduces substantial uncorrelated noise in the radiative fluxes at the surface and heating rates, but it reduces the cost associated to the spectral integration. Therefore, it allows to update the radiative transfer computations more frequently and to perform them on a denser spatial grid. We evaluate how this approach applies to 5 days weather forecasts by testing different combinations of temporal and spectral sampling at high spatial resolution. We assess the impact of each radiation configuration on the forecast, by comparing the near-surface temperatures to observations from synoptic stations. The results show that a combination of spectrally sparse but temporally and spatially dense radiation calculations has the potential to reduce the forecast errors, particularly those associated with underresolved topography and stable nocturnal boundary layers, with affordable computational costs. A. Bozzo R. Pincus I. Sandu J.-J. Morcrette 2015-10-07T14:34:42Z 2015-10-07T14:34:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1222 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1222 2015-10-07T14:34:42Z Spatial variability of seasonal extreme precipitation in the western United States We examine the characteristics of 3 day total extreme precipitation in the western United States. Coherent seasonal spatial patterns of timing and magnitude are evident in the data, motivating a seasonally based analysis. Using a clustering method that is consistent with extreme value theory, we identify coherent regions for extremes that vary seasonally. Based on storm back trajectory analysis, we demonstrate unique moisture sources and dominant moisture pathways for each spatial region. In the winter the Pacific Ocean is the dominant moisture source across the west, but in other seasons the Gulf of Mexico, the Gulf of California, and the land surface over the midwestern U.S. play an important role. We find the El Niño–Southern Oscillation (ENSO) to not have a strong impact on dominant moisture delivery pathways or moisture sources. The frequency of extremes under ENSO is spatially coherent and seasonally dependent with certain regions tending to have more (less) frequent extreme events in El Niño (La Niña) conditions. C. Bracken B. Rajagopalan M. A. Alexander S. Gangopadhyay 2017-07-07T20:31:03Z 2017-07-07T20:31:03Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1515 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1515 2017-07-07T20:31:03Z Spatial Bayesian hierarchical modeling of precipitation extremes over a large domain We propose a Bayesian hierarchical model for spatial extremes on a large domain. In the data layer a Gaussian elliptical copula having generalized extreme value (GEV) marginals is applied. Spatial dependence in the GEV parameters is captured with a latent spatial regression with spatially varying coefficients. Using a composite likelihood approach, we are able to efficiently incorporate a large precipitation data set, which includes stations with missing data. The model is demonstrated by application to fall precipitation extremes at approximately 2600 stations covering the western United States, −125°E to −100°E longitude and 30°N–50°N latitude. The hierarchical model provides GEV parameters on a 1/8° grid and, consequently, maps of return levels and associated uncertainty. The model results indicate that return levels and their associated uncertainty have a well-defined spatial structure. Maps of return levels provide information about the spatial variations of the risk of extreme precipitation in the western US and is expected to be useful for infrastructure planning. C. Bracken B. Rajagopalan L. Cheng W. Kleiber S. Gangopadhyay 2012-09-28T20:53:18Z 2013-04-24T20:47:37Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/278 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/278 2012-09-28T20:53:18Z Recent changes in freezing level heights in the Tropics with implications for the deglacierization of high mountain regions The height of the freezing level in the tropical atmosphere (the free air 0°C isotherm) has increased across most of the region, particularly in the outer Tropics. In the tropical Andes, south of the Equator, high elevation surface temperatures and upper air data show a similar trend in temperature, of ∼0.1°C/decade over the last 50 years. Meteorological observations at 5680 m on the summit of the Quelccaya Ice Cap, the largest ice mass in the Tropics, indicate that daily maximum temperatures often exceed 0°C from October–May, and rise well above freezing for much of the year around the ice cap margin at 5200 m. This is consistent with observations of a rise in the percolation facies (an indicator of surface melting) in recent decades, and other observations of marginal recession, showing that the ice cap is rapidly losing mass. Similar conditions are likely to be affecting other high elevation ice caps and glaciers in Ecuador, Perú and Bolivia, with important implications for water supplies in the region. Over the Tropics as a whole, freezing level height (FLH) is closely related to mean SSTs, with inter-annual variations in FLH controlled by the phase of ENSO variability. More extensive monitoring of climatic conditions at high elevations in the mountains of the Tropics is urgently needed. R. S. Bradley F. T. Keimig H. F. Diaz D. R. Hardy 2012-09-22T00:01:33Z 2013-05-10T20:20:41Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/109 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/109 2012-09-22T00:01:33Z Threats to water supplies in the tropical Andes Climate models predict that greenhouse warming will cause temperatures to rise faster at higher than at lower altitudes. In the tropical Andes, glaciers may soon disappear, with potentially grave consequences for water supplies. R. S. Bradley M. Vuille H. F. Diaz W. Vergara 2016-10-13T18:54:16Z 2016-10-13T18:54:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1397 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1397 2016-10-13T18:54:16Z The Medieval Quiet Period For several centuries in early Medieval times the climate system was relatively unperturbed by natural forcing factors, resulting in a unique period of climate stability. We argue that this represents a reference state for the Common Era, well before anthropogenic forcing became the dominant driver of the climate system. R. S. Bradley H. Wanner H. F. Diaz 2017-07-07T20:48:02Z 2017-07-07T20:48:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1517 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1517 2017-07-07T20:48:02Z Emergent anthropogenic trends in California Current upwelling Upwelling in the California Current System (CCS) sustains a productive ecosystem and is mediated by alongshore, equatorward wind stress. A decades-old hypothesis proposes that global warming will accelerate these upwelling favorable winds. Recent analyses provide empirical support for upwelling intensification in the poleward portion of the CCS. However, these studies rely on proxies for upwelling and are limited in their ability to distinguish anthropogenic forcing from internal climate variability. Here we estimate simulated changes in CCS upwelling from 1920 to 2100 using monthly output from a single climate model ensemble, where divergences among simulations can be attributed entirely to internal climate variability. Our projections suggest that CCS upwelling will become more intense in the spring and less intense in the summer as a result of anthropogenic climate change. Anthropogenic changes in upwelling will emerge primarily in the second half of the century. R. X. Brady M. A. Alexander N. S. Lovenduski R. R. Rykaczewski 2012-11-15T16:52:21Z 2013-05-07T23:22:57Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/764 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/764 2012-11-15T16:52:21Z How to Take Climate Change Into Account: A Guidance Document for Judges Adjudicating Water Disputes This report is intended for use by federal, state, and administrative judges who are confronted with a legal dispute involving a water resource that is alleged to be impacted by climate change. It may be useful as well for attorneys litigating or experts working on water adjudications. The purpose of this document is to summarize the manner in which climate change may impact rights and frameworks established under state and federal law concerning water resources and to anticipate the issues that water-related climate claims will pose to legal decisionmakers. This report arose out of the November 11-12, 2009, workshop, "Water Law and Climate Change," held in Reno, Nevada, and sponsored by the National Judicial College and Dividing the Waters, a nonprofit organization of federal and state water adjudicators. No judge who attended the workshop has reviewed or approved of the content of this document. This document does not reflect the personal opinion of any individual judge. C. Brickey K. Engel K. Jacobs . . . B. Udall 2012-09-28T21:02:02Z 2013-05-03T14:50:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/279 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/279 2012-09-28T21:02:02Z Using Dual-Polarized Radar and Dual-Frequency Profiler for DSD Characterization: A Case Study from Darwin, Australia Comparisons are made between the reflectivity Z, median volume diameter D0, and rain rate R from a dual-frequency profiler and the C-band polarimetric radar (C-POL), which are both located near Darwin, Australia. Examples from the premonsoon "buildup" regime and the monsoon (oceanic) regime are used to illustrate the excellent agreement between the dual-profiler retrievals and the polarimetric radar-based retrievals. This work builds on similar works that were limited in scope to shallow tropical showers and predominantly stratiform rain events. The dual-frequency profiler retrievals of D0 and R herein are based on ensemble statistics, whereas the polarimetric radar retrievals are based on algorithms derived by using one season of disdrometer data from Darwin along with scattering simulations. The latest drop shape versus D relation is used as well as the canting angle distribution results obtained from the 80-m fall bridge experiment in the scattering simulations. The scatterplot of D0 from dual-frequency profiler versus Zdr measurements from C-POL is shown to be consistent not only with the theoretical simulations and prior data but also within prior predicted error bars for both stratiform rain as well as convective rain. Based on dual-frequency profiler–retrieved gamma drop size distribution parameters, a new smoothly varying "separator" indexing scheme has been developed that classifies between stratiform and convective rain types, including a continuous "transition" region between the two. This indexing technique has been applied on a number of low-elevation-angle plan position indicator (PPI) sweeps with the C-POL from the two regime examples, to construct "unconditioned" histograms of D0 in stratiform and convective rain (to within the sensitivity of the radar). With reference to the latter, it is demonstrated that the distribution of D0 is different in the buildup example than in the monsoon example, because of the differences in both the microphysical and kinematic features between the two regimes. In particular, (i) the mean D0 is significantly larger in the buildup example than in the monsoon example, irrespective of rain type; (ii) the histogram width (or standard deviation) is much larger for the buildup example than the monsoon example, irrespective of rain type; and (iii) the histogram skewness is negative for the monsoon regime example because of a lack of larger D0 values, whereas the buildup histogram is positively skewed irrespective of rain type. V. N. Bringi C. R. Williams 2015-10-07T14:33:32Z 2015-10-07T14:33:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1224 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1224 2015-10-07T14:33:32Z Climate-change adaptation on rangelands: linking regional exposure with diverse adaptive capacity The ecological consequences of climate change are predicted to vary greatly throughout US rangelands. Projections show warming and drying in the southern Great Plains and the Southwest, warmer and drier summers with reduced winter snowpack in the Northwest, and warmer and wetter conditions in the northern Great Plains. Primarily through their combined effects on soil water availability, these climatic changes will modify plant production and community composition, which will, in turn, affect the livelihoods of humans who rely upon livestock grazing. The ability of rangeland managers to assess risk and prepare for climate change varies greatly and reflects their different adaptive capacities. Geographically specific exposure to climate change and a diverse adaptive capacity to counteract these changes will require development of varied adaptation strategies that can accommodate the various needs and abilities of livestock managers. D. D. Briske L. A. Joyce H. W. Polley J. R. Brown K. Wolter J. A. Morgan B. A. McCarl D. W. Bailey 2012-09-28T21:02:13Z 2013-04-25T14:58:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/280 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/280 2012-09-28T21:02:13Z Marine Observations of Old Weather Weather observations are vital for climate change monitoring and prediction. For the world's oceans, there are many meteorological and oceanographic observations available back to the mid-twentieth century, but coverage is limited in earlier periods, and particularly also during the two world wars. Before 1850 there are currently very few instrumental observations available. Consequently, detailed observational estimates of surface climate change can be made only back to the mid-nineteenth century. To improve and extend this early coverage, scientists need more observations from these periods. Fortunately, many such observations exist in logbooks, reports, and other paper records, but their inclusion in the climatic datasets requires that these paper records be abstracted from the world's archives, digitized into an electronic form, and blended into existing climate databases. As a first step in this direction, selected Royal Navy logbooks from the period of 1938–47, kept in the U.K. National Archives, have been photographed and digitized. These have provided more than 1,500,000 new observations for this period, and a preliminary analysis has shown significant improvements to the record of climate change in the mid-twentieth century. P. Brohan R. Allan J. E. Freeman A. M. Waple D. Wheeler C. Wilkinson S. D. Woodruff 2015-04-20T20:13:10Z 2015-04-29T14:16:37Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1123 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1123 2015-04-20T20:13:10Z Acoustic Green's function extraction from ambient noise in a coastal ocean environment We report on the results of an underwater acoustic field experiment conducted in December 2012 on the continental shelf off the Florida Keys in water of approximately 100 m depth. Ambient noise was recorded concurrently on three moored near-bottom instruments with horizontal separations of approximately 5 km, 10 km, and 15 km. We focus in this letter on instrument pairs with 5 km and 10 km separations. Consistent with theoretical predictions, coherent sums of many realizations of cross correlations of ambient noise records at two measurement locations are shown to yield approximations to deterministic acoustic Green's functions that describe propagation between those two locations. The results presented demonstrate the feasibility of extracting information suitable for use in tomographic inversions from measurements of underwater acoustic ambient noise. M. G. Brown O. A. Godin N. J. Williams N. A. Zabotin L. Y. Zabotina G. J. Banker 2016-10-13T22:54:45Z 2016-10-13T22:54:45Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1398 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1398 2016-10-13T22:54:45Z Ocean acoustic remote sensing using ambient noise: results from the Florida Straits Noise interferometry is the process by which approximations to acoustic Green's functions, which describe sound propagation between two locations, are estimated by cross-correlating time series of ambient noise measured at those locations. Noise-interferometry-based approximations to Green's functions can be used as the basis for a variety of inversion algorithms, thereby providing a purely passive alternative to active-source ocean acoustic remote sensing. In this paper we give an overview of results from noise interferometry experiments conducted in the Florida Straits at 100 m depth in December 2012, and at 600 m depth in September/October 2013. Under good conditions for noise interferometry, estimates of cross-correlation functions are shown to allow one to perform advanced phase-coherent signal processing techniques to perform waveform inversions, estimate currents by exploiting non-reciprocity, perform time-reversal/back-propagation calculations and investigate modal dispersion using time-warping techniques. Conditions which are favourable for noise interferometry are identified and discussed. M. G. Brown O. A. Godin X. Zang J. S. Ball N. A. Zabotin L. Y. Zabotina N. J. Williams 2012-09-22T00:06:30Z 2013-05-13T15:18:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/110 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/110 2012-09-22T00:06:30Z High resolution vertical distributions of NO3 and N2O5 through the nocturnal boundary layer The shallow mixing depth and vertical stratification of the lowest levels of the atmosphere at night has implications for the chemistry of nitrogen oxides emitted from the surface. Here we report vertical profiles of NO3, N2O5 and O3 measured from in-situ instruments on a movable carriage on a 300 m tower. The study offers high-resolution (<1 m) vertical distributions of both NO3 and N2O5 and shows that the nocturnal mixing ratios of these compounds vary widely over short vertical distance scales (10 m or less). Furthermore, there are systematic differences in the steady state lifetimes of NO3 and NO5 and in the partitioning among nitrogen oxides between different near-surface layers. These differences imply that NO3 and N2O5 occupy distinct chemical regimes as a function of altitude, potentially serving as sinks for nitrogen oxides and O3 near the surface but as reservoirs of NOx and O3 aloft. S. S. Brown W. P. Dubé H. D. Osthoff D. Wolfe W. M. Angevine A. R. Ravishankara 2012-10-15T23:23:15Z 2013-05-07T17:26:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/294 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/294 2012-10-15T23:23:15Z High resolution vertical distributions of NO3 and N2O5 through the nocturnal boundary layer The shallow mixing depth and vertical stratification of the lowest levels of the atmosphere at night has implications for the chemistry of nitrogen oxides emitted from the surface. Here we report vertical profiles of NO3, N2O5 and O3 measured from in-situ instruments on a movable carriage on a 300 m tower. The study offers high-resolution (<1 m) vertical distributions of both NO3 and N2O5 and shows that the nocturnal mixing ratios of these compounds vary widely over short vertical distance scales (10 m or less). Furthermore, there are systematic differences in the steady state lifetimes of NO3 and N2O5 and in the partitioning among nitrogen oxides between different near-surface layers. These differences imply that NO3 and N2O5 occupy distinct chemical regimes as a function of altitude, potentially serving as sinks for nitrogen oxides and O3 near the surface but as reservoirs of NOx and O3 aloft. S. S. Brown W. P. Dubé H. D. Osthoff D. E. Wolfe W. M. Angevine A. R. Ravishankara 2013-08-26T21:53:17Z 2013-08-26T22:06:04Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/942 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/942 2013-08-26T21:53:17Z Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT): Overview of a wintertime air chemistry field study in the front range urban corridor of Colorado The Nitrogen, Aerosol Composition, and Halogens on a Tall Tower (NACHTT) field experiment took place during late winter, 2011, at a site 33 km north of Denver, Colorado. The study included fixed-height measurements of aerosols, soluble trace gases, and volatile organic compounds near surface level, as well as vertically resolved measurements of nitrogen oxides, aerosol composition, soluble gas-phase acids, and halogen species from 3 to 270 m above ground level. There were 1928 individual profiles during the three-week campaign to characterize trace gas and aerosol distributions in the lower levels of the boundary layer. Nitrate and ammonium dominated the ionic composition of aerosols and originated primarily from local or regional sources. Sulfate and organic matter were also significant and were associated primarily with longer-range transport to the region. Aerosol chloride was associated primarily with supermicron size fractions and was always present in excess of gas-phase chlorine compounds. The nighttime radical reservoirs, nitryl chloride, ClNO2, and nitrous acid, HONO, were both consistently present in nighttime urban air. Nitryl chloride was especially pronounced in plumes from large point sources sampled aloft at night. Nitrous acid was typically most concentrated near the ground surface and was the dominant contributor (80%) to diurnally averaged primary OH radical production in near-surface air. Large observed mixing ratios of light alkanes, both in near-surface air and aloft, were attributable to local emissions from oil and gas activities. S. S. Brown J. A. Thornton W. C. Keene . . . D. E. Wolfe 2015-11-19T21:27:39Z 2015-11-19T21:27:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1285 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1285 2015-11-19T21:27:39Z A collection of sub-daily pressure and temperature observations for the early instrumental period with a focus on the "year without a summer" 1816 The eruption of Mount Tambora (Indonesia) in April 1815 is the largest documented volcanic eruption in history. It is associated with a large global cooling during the following year, felt particularly in parts of Europe and North America, where the year 1816 became known as the "year without a summer". This paper describes an effort made to collect surface meteorological observations from the early instrumental period, with a focus on the years of and immediately following the eruption (1815–1817). Although the collection aimed in particular at pressure observations, correspondent temperature observations were also recovered. Some of the series had already been described in the literature, but a large part of the data, recently digitised from original weather diaries and contemporary magazines and newspapers, is presented here for the first time. The collection puts together more than 50 sub-daily series from land observatories in Europe and North America and from ships in the tropics. The pressure observations have been corrected for temperature and gravity and reduced to mean sea level. Moreover, an additional statistical correction was applied to take into account common error sources in mercury barometers. To assess the reliability of the corrected data set, the variance in the pressure observations is compared with modern climatologies, and single observations are used for synoptic analyses of three case studies in Europe. All raw observations will be made available to the scientific community in the International Surface Pressure Databank. Y. Brugnara R. Auchmann S. Brönnimann . . . G. P. Compo et al. 2012-11-15T16:54:37Z 2013-05-07T23:20:45Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/766 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/766 2012-11-15T16:54:37Z Collaboration of the Weather and Climate Communities to Advance Subseasonal-to-Seasonal Prediction The World Weather Research Programme (WWRP) and the World Climate Research Programme (WCRP) have identified collaborations and scientific priorities to accelerate advances in analysis and prediction at subseasonal-to-seasonal time scales, which include i) advancing knowledge of mesoscale–planetary-scale interactions and their prediction; ii) developing high-resolution global–regional climate simulations, with advanced representation of physical processes, to improve the predictive skill of subseasonal and seasonal variability of high-impact events, such as seasonal droughts and floods, blocking, and tropical and extratropical cyclones; iii) contributing to the improvement of data assimilation methods for monitoring and predicting used in coupled ocean–atmosphere–land and Earth system models; and iv) developing and transferring diagnostic and prognostic information tailored to socioeconomic decision making. The document puts forward specific underpinning research, linkage, and requirements necessary to achieve the goals of the proposed collaboration. G. Brunet M. Shapiro B. Hoskins M. Moncrieff R. M. Dole G. N. Kiladis et al. 2014-01-09T00:46:22Z 2014-01-09T00:46:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1010 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1010 2014-01-09T00:46:22Z Impact of dust radiative forcing in snow on accuracy of operational runoff prediction in the Upper Colorado River Basin Accurate prediction of snowmelt runoff is critical in the US Intermountain West, where water demand is increasing and snow patterns are shifting. Here, we show that errors in the National Weather Service Colorado Basin River Forecast Center's operational streamflow predictions are correlated with the interannual variability of dust radiative forcing in snow. With data from 2000–2010, we show that errors in snowmelt period streamflow prediction for the southern Colorado Rockies are linearly related to melt period dust radiative forcing in snow as inferred from NASA Moderate Resolution Imaging Spectroradiometer data, which ranged interannually from 20 to 80 W m−2. Each 10 W m−2 change of melt period dust forcing resulted in a corresponding change in runoff prediction bias of 10.0% ± 1.5% and a 1.5 ± 0.6 day shift in runoff center of mass. Accounting for bias introduced by dust forcing could improve streamflow prediction in regions prone to dust deposition in the snowpack. A. C. Bryant T. H. Painter J. S. Deems S. M. Bender 2012-05-04T16:12:44Z 2013-05-06T16:07:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/23 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/23 2012-05-04T16:12:44Z Ozone highs and associated flow features in the first half of the twentieth century in different data. sets. In order to better understand weather extremes, their relation to the large-scale climate variability, and their possible changes over time, observation-based atmospheric data sets are required that reach back in time as far as possible and that provide information on the 3-dimensional structure of the atmosphere. A number of new such data sets have been published in recent years, including historical observations, reanalyses, and reconstructions, some of which reach back into the nineteenth century. However, their usefulness for studying weather extremes remains to be shown. Here we compare some of these historical data sets in the first half of the twentieth century, focusing on one specific type of extreme, namely "ozone highs". Using historical total ozone observations as a starting point, we assess dynamical links between total ozone, the flow near the tropopause, and tropospheric circulation in the "Twentieth Century Reanalysis" (20CR), historical radiosonde and aircraft observations, and hand drawn historical maps. Selected cases are presented for two regions (Europe and China). Ozone highs over Europe in the 1920s to 1950s were qualitatively well reproduced in 20CR and could mostly be interpreted in the context of cut-off lows. Some of these coincided with a blocking high over the North Atlantic or with vigorous cold-air outbreaks. One of these cases is analysed in more detail. Ozone highs over China in the 1930s may have been related to changes in the jet stream and the subtropical tropopause, but they were not always well reproduced in 20CR. The results demonstrate that, in many of the cases, the available data allow a dynamical interpretation. This confirms the potential of the available data and techniques to extend the length of atmospheric data sets suitable for studying extremes. S. Brönnimann G. P. Compo 2012-11-06T17:46:56Z 2013-05-07T19:22:04Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/486 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/486 2012-11-06T17:46:56Z New approaches for extending the twentieth century climate record Studying twentieth century climate is a key to understanding future climate change. Relatively little is still known, however, about climate variability in the first half of the century. Much could be learned from the relatively large climatic variations that occurred during that first half, including the decade-long "Dust Bowl" droughts of the 1930s and the warming of the Arctic from 1920 to 1945. Poor digital data availability prior to around 1948 has hindered previous work to understand these important climatic variations. S. Brönnimann G. P. Compo P. D. Sardeshmukh R. Jenne A. Sterin 2012-11-13T17:22:23Z 2013-05-02T16:27:19Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/615 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/615 2012-11-13T17:22:23Z Early ship-based upper-air data and comparison with the Twentieth Century Reanalysis Extension of 3-D atmospheric data products back into the past is desirable for a wide range of applications. Historical upper-air data are important in this endeavour, particularly in the maritime regions of the tropics and the southern hemisphere, where observations are extremely sparse. Here we present newly digitized and re-evaluated early ship-based upper-air data from two cruises: (1) kite and registering balloon profiles from onboard the ship SMS Planet on a cruise from Europe around South Africa and across the Indian Ocean to the western Pacific in 1906/1907, and (2) ship-based radiosonde data from onboard the MS Schwabenland on a cruise from Europe across the Atlantic to Antarctica and back in 1938/1939. We describe the data and provide estimations of the errors. We compare the data with a recent reanalysis (the Twentieth Century Reanalysis Project, 20CR, Compo et al., 2011) that provides global 3-D data back to the 19th century based on an assimilation of surface pressure data only (plus monthly mean sea-surface temperatures). In cruise (1), the agreement is generally good, but large temperature differences appear during a period with a strong inversion. In cruise (2), after a subset of the data are corrected, close agreement between observations and 20CR is found for geopotential height (GPH) and temperature notwithstanding a likely cold bias of 20CR at the tropopause level. Results are considerably worse for relative humidity, which was reportedly inaccurately measured. Note that comparing 20CR, which has limited skill in the tropical regions, with measurements from ships in remote regions made under sometimes difficult conditions can be considered a worst case assessment. In view of that fact, the anomaly correlations for temperature of 0.3–0.6 in the lower troposphere in cruise (1) and of 0.5–0.7 for tropospheric temperature and GPH in cruise (2) are considered as promising results. Moreover, they are consistent with the error estimations. The results suggest room for further improvement of data products in remote regions. S. Brönnimann G. P. Compo R. Spadin R. Allan W. Adam 2016-04-11T21:09:28Z 2016-04-11T21:10:24Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1315 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1315 2016-04-11T21:09:28Z Southward shift of the northern tropical belt from 1945 to 1980 Changes in the position and width of the tropical belt are societally and ecologically relevant, because they are associated with shifts of the subtropical dry zones. The tropical belt has widened since about 1980, but little is known about its earlier variability. Here we analyse historical surface and upper-level observations, three global reanalysis data sets, and a reconstruction of total column ozone, to show that the northern tropical edge retracted from 1945 to 1980, while the northern Hadley cell shifted southwards in both summer and winter. We present chemistry–climate model simulations that reproduce the retraction and southward shift. We find that retraction of the tropical belt was largely due to cooling sea-surface temperatures north of the Equator and warming south of the Equator, most prominently over the Atlantic. Substantial hydroclimatic anomalies such as European droughts of the 1940s and 1950s and the Sahel drought of the 1970s were associated with this shift of the Hadley cell. Our results suggest that multidecadal changes in the position of the northern Hadley cell are an important component of climate variability. S. Brönnimann A. M. Fischer E. Rozanov P. Poli G. P. Compo P. D. Sardeshmukh 2013-01-31T21:35:52Z 2013-04-24T17:41:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/882 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/882 2013-01-31T21:35:52Z A multi-data set comparison of the vertical structure of temperature variability and change over the Arctic during the past 100 years We compare the daily, interannual, and decadal variability and trends in the thermal structure of the Arctic troposphere using eight observation-based, vertically resolved data sets, four of which have data prior to 1948. Comparisons on the daily scale between historical reanalysis data and historical upper-air observations were performed for Svalbard for the cold winters 1911/1912 and 1988/1989, the warm winters 1944/1945 and 2005/2006, and the International Geophysical Year 1957/1958. Excellent agreement is found at mid-tropospheric levels. Near the ground and at the tropopause level, however, systematic differences are identified. On the interannual time scale, the correlations between all data sets are high, but there are systematic biases in terms of absolute values as well as discrepancies in the magnitude of the variability. The causes of these differences are discussed. While none of the data sets individually may be suitable for trend analysis, consistent features can be identified from analyzing all data sets together. To illustrate this, we examine trends and 20-year averages for those regions and seasons that exhibit large sea-ice changes and have enough data for comparison. In the summertime Pacific Arctic and the autumn eastern Canadian Arctic, the lower tropospheric temperature anomalies for the recent two decades are higher than in any previous 20-year period. In contrast, mid-tropospheric temperatures of the European Arctic in the wintertime of the 1920s and 1930s may have reached values as high as those of the late 20th and early 21st centuries. S. Brönnimann A. N. Grant G. P. Compo et al. 2012-05-04T17:06:41Z 2013-05-03T17:10:06Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/25 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/25 2012-05-04T17:06:41Z Extreme winds at northern mid-latitudes since 1871 Studying a sufficiently large sample of extremes or analysing the statistics of their occurrence, including trends, is hampered by the length of the existing observation-based record. New data sets such as the Twentieth Century Reanalysis (20CR), which consists of an ensemble of 56 members, significantly extend our record back in time. In this paper, we present examples of extremes of winds at northern hemisphere mid-latitudes in 20CR to illustrate challenges and opportunities for analysing extremes over a longer period than previously possible. For four representative storms from Europe and North America, 20CR provides a relatively good depiction of the synoptic-scale meteorological development, although it misses smaller scale features as well as local effects due to orography. For analysing trends of extreme winds, it is shown that the individual ensemble members should be used, rather than the ensemble mean, which appears to be biased towards lower wind speeds early in the record. For the studied locations, decadal variability and trends can best be characterised after around 1950, when the ensemble variance remains consistent. Different methodological approaches for studying changes in extreme winds are discussed. Finally, we show hemispheric maps of trends in extreme wind speeds since 1950. S. Brönnimann O. Martius H. von Waldow C. Welker J. Luterbacher G. P. Compo P. D. Sardeshmukh T. Usbeck 2012-12-21T20:29:15Z 2013-05-07T18:42:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/844 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/844 2012-12-21T20:29:15Z Observing ice clouds in the submillimeter spectral range: the CloudIce mission proposal for ESA's Earth Explorer 8 Passive submillimeter-wave sensors are a way to obtain urgently needed global data on ice clouds, particularly on the so far poorly characterized "essential climate variable" ice water path (IWP) and on ice particle size. CloudIce was a mission proposal to the European Space Agency ESA in response to the call for Earth Explorer 8 (EE8), which ran in 2009/2010. It proposed a passive submillimeter-wave sensor with channels ranging from 183 GHz to 664 GHz. The article describes the CloudIce mission proposal, with particular emphasis on describing the algorithms for the data-analysis of submillimeter-wave cloud ice data (retrieval algorithms) and demonstrating their maturity. It is shown that we have a robust understanding of the radiative properties of cloud ice in the millimeter/submillimeter spectral range, and that we have a proven toolbox of retrieval algorithms to work with these data. Although the mission was not selected for EE8, the concept will be useful as a reference for other future mission proposals. S. A Buehler E. Defer F. Evans . . . A. J. Gasiewski 2012-11-09T20:31:32Z 2013-05-08T15:39:57Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/587 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/587 2012-11-09T20:31:32Z An upper tropospheric humidity data set from operational satellite microwave data 183.31 GHz observations from the Advanced Microwave Sounding Unit B (AMSU-B) instruments onboard the NOAA 15, 16, and 17 satellites were used to derive a new data set of Upper Tropospheric Humidity (UTH). The data set consist of monthly median and mean data on a 1.5° latitude-longitude grid between 60°S and 60°N, and covers the time period of January 2000 to February 2007. The data from all three instruments are very consistent, with relative difference biases of less than 4% and relative difference standard deviations of 7%. Radiometric contributions by high ice clouds and by the Earth's surface affect the measurements in certain areas. The uncertainty due to clouds is estimated to be up to approximately 10%RH in areas with deep convection. The uncertainty associated with contamination from surface emission can exceed 10%RH in midlatitude winter, where the data therefore should be regarded with caution. Otherwise the surface influence appears negligible. The paper also discusses the UTH median climatology and seasonal cycle, which are found to be broadly consistent with UTH climatologies from other sensors. Finally, the paper presents an initial validation of the new data set against IR satellite data and radiosonde data. The observed biases of up to 9%RH (wet bias relative to HIRS) were found to be broadly consistent with expectations based on earlier studies. The observed standard deviations against all other data sets were below 6%RH. The UTH data are available to the scientific community on http://www.sat.ltu.se. S. A Buehler M. Kuvatov V. O. John M. Milz B. J. Soden D. L. Jackson J. Notholt 2016-12-19T17:00:28Z 2017-01-03T16:44:15Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1448 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1448 2016-12-19T17:00:28Z Barotropic and Baroclinic Eddy Feedbacks in the Midlatitude Jet Variability and Responses to Climate Change-Like Thermal Forcings Studies have suggested that the persistence in the meridional vacillation of the midlatitude jet (i.e., annular mode timescale) in comprehensive climate models is related to the model biases in climatological jet latitude, with important implications for projections of future climates and midlatitude weather events. Through the use of the recently developed finite-amplitude wave activity formalism and feedback quantifying techniques, this paper has quantified the role of barotropic and baroclinic eddy feedbacks in annular mode timescales using an idealized dry atmospheric model. The eddy-mean flow interaction that characterizes the persistent anomalous state of the midlatitude jet depends on processes associated with the lower-tropospheric source of vertically propagating Rossby waves, baroclinic mechanisms, and processes associated with upper-tropospheric wave propagation and breaking, barotropic mechanisms. A variety of climate change-like thermal forcings are used to generate a range of meridional shifts in the midlatitude eddy-driven jet. The idealized model shows a reduction in annular mode timescale associated with an increase in jet latitude, similar to comprehensive climate models. This decrease in timescale can be attributed to a similar decrease in the strength of the barotropic eddy feedback, which, in the positive phase of the annular mode, is characterized by anomalous potential vorticity (PV) mixing on the equatorward flank of the climatological jet. The decrease in subtropical PV mixing is, in turn, associated with a stronger subtropical jet as the eddy-driven jet is more distant from the subtropics. These results highlight the importance of subtropical eddy-mean flow interactions for the persistence of an eddy-driven jet. D. A. Burrows G. Chen L. Sun 2012-09-25T22:03:48Z 2013-05-07T23:14:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/214 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/214 2012-09-25T22:03:48Z Stratospheric Dynamics N/A N. A. Butchart A. J. Charlton-Perez I. Cionni S. C. Hardiman K. Krueger P. Kushner P. Newman S. M. Osprey J. Perlwitz F. Sassi M. Sigmond L. Wang 2012-11-15T16:56:53Z 2013-05-08T14:58:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/767 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/767 2012-11-15T16:56:53Z Multimodel climate and variability of the stratosphere The stratospheric climate and variability from simulations of sixteen chemistry-climate models is evaluated. On average the polar night jet is well reproduced though its variability is less well reproduced with a large spread between models. Polar temperature biases are less than 5 K except in the Southern Hemisphere (SH) lower stratosphere in spring. The accumulated area of low temperatures responsible for polar stratospheric cloud formation is accurately reproduced for the Antarctic but underestimated for the Arctic. The shape and position of the polar vortex is well simulated, as is the tropical upwelling in the lower stratosphere. There is a wide model spread in the frequency of major sudden stratospheric warnings (SSWs), late biases in the breakup of the SH vortex, and a weak annual cycle in the zonal wind in the tropical upper stratosphere. Quantitatively, "metrics" indicate a wide spread in model performance for most diagnostics with systematic biases in many, and poorer performance in the SH than in the Northern Hemisphere (NH). Correlations were found in the SH between errors in the final warming, polar temperatures, the leading mode of variability, and jet strength, and in the NH between errors in polar temperatures, frequency of major SSWs, and jet strength. Models with a stronger QBO have stronger tropical upwelling and a colder NH vortex. Both the qualitative and quantitative analysis indicate a number of common and long-standing model problems, particularly related to the simulation of the SH and stratospheric variability. N. A. Butchart I. Cionni A. J. Charlton-Perez . . . J. Perlwitz et al. 2017-05-05T20:29:09Z 2017-05-05T20:29:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1502 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1502 2017-05-05T20:29:09Z Chapter 10: Remote Sensing State-of-the-art remote-sensing techniques applicable to the investigation of ice formation and evolution are described. Ground-based and spaceborne measurements with lidar, radar and radiometric techniques are discussed together with a global view on past and ongoing remote-sensing measurement campaigns concerned with the study of ice formation and evolution. The article has the intention of a literature study and should illustrate the major efforts that are currently taken in the field of remote sensing of atmospheric ice. Since other chapters of this monograph mainly focus on aircraft in-situ measurements, special emphasis is put on active remote sensing instruments and synergies between aircraft in-situ measurements and passive remote sensing methods. The article concentrates on homogeneous and heterogeneous ice formation in the troposphere because this is a major topic of this monograph. Furthermore, methods that deliver direct, process level information about ice formation are elaborated with a special emphasis on active remote sensing methods. Passive remote sensing methods are also dealt with but only in the context of synergy with aircraft in-situ measurements. J. Bühl S. Alexander A. Crewell A. J. Heymsfield H. Kalesse A. P. Khain M. Maahn K. Van-Tricht M. Wendisch 2012-11-06T17:52:01Z 2012-11-06T17:52:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/487 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/487 2012-11-06T17:52:01Z Bringing together the most advanced radiative transfer tools for cloudy atmospheres The interaction of clouds with solar and terrestrial radiation is one of the most important topics of climate research. In recent years it has been recognized that only a full three-dimensional (3D) treatment of this interaction can provide answers to many climate and remote sensing problems, leading to the worldwide development of numerous 3D radiative transfer (RT) codes. The international Intercomparison of 3D Radiation Codes (I3RC), described in this paper, sprung from the natural need to compare the performance of these 3D RT codes used in a variety of current scientific work in the atmospheric sciences. I3RC supports intercomparison and development of both exact and approximate 3D methods in its effort to 1) understand and document the errors/limits of 3D algorithms and their sources; 2) provide "baseline" cases for future code development for 3D radiation; 3) promote sharing and production of 3D radiative tools; 4) derive guidelines for 3D radiative tool selection; and 5) improve atmospheric science education in 3D RT. Results from the two completed phases of I3RC have been presented in two workshops and are expected to guide improvements in both remote sensing and radiative energy budget calculations in cloudy atmospheres. R. F. Cahalan L. Oreopoulos A. Marshak K. F. Evans A. B. Davis R. Pincus et al. 2016-07-08T16:21:20Z 2017-04-11T15:41:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1364 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1364 2016-07-08T16:21:20Z The influence of tropical forcing on extreme winter precipitation in the western Himalaya Within the Karakoram and western Himalaya (KH), snowfall from winter westerly disturbances (WD) maintains the region's snowpack and glaciers, which melt seasonally to sustain water resources for downstream populations. WD activity and subsequent precipitation are influenced by global atmospheric variability and tropical-extratropical interactions. On interannual time-scales, El Niño related changes in tropical diabatic heating induce a Rossby wave response over southwest Asia that is linked with enhanced dynamical forcing of WD and available moisture. Consequently, extreme orographic precipitation events are more frequent during El Niño than La Niña or neutral conditions. A similar spatial pattern of tropical diabatic heating is produced by the MJO at intraseasonal scales. In comparison to El Niño, the Rossby wave response to MJO activity is less spatially uniform over southwest Asia and varies on shorter time-scales. This study finds that the MJO's relationship with WD and KH precipitation is more complex than that of ENSO. Phases of the MJO propagation cycle that favor the dynamical enhancement of WD simultaneously suppress available moisture over southwest Asia, and vice versa. As a result, extreme precipitation events in the KH occur with similar frequency in most phases of the MJO, however, there is a transition in the relative importance of dynamical forcing and moisture in WD to orographic precipitation in the KH as the MJO evolves. These findings give insight into the dynamics and predictability of extreme precipitation events in the KH through their relationship with global atmospheric variability, and are an important consideration in evaluating Asia's water resources. F. Cannon L. M. V. Carvalho C. Jones A. Hoell J. Norris G. N. Kiladis A. A. Tahir 2017-04-11T23:06:43Z 2017-04-11T23:06:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1486 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1486 2017-04-11T23:06:43Z Effects of topographic smoothing on the simulation of winter precipitation in High Mountain Asia Numerous studies have projected future changes in High Mountain Asia water resources based on temperature and precipitation from global circulation models (GCMs) under future climate scenarios. Although the potential benefit of such studies is immense, coarse grid-scale GCMs are unable to resolve High Mountain Asia's complex topography and thus have a biased representation of regional weather and climate. This study investigates biases in the simulation of physical mechanisms that generate snowfall and contribute to snowpack in High Mountain Asia in coarse topography experiments using the Weather Research and Forecasting model. Regional snowpack is event driven, thus 33 extreme winter orographic precipitation events are simulated at fine atmospheric resolution with 6.67 km resolution topography and smoothed 1.85° × 1.25° GCM topography. As with many modified topography experiments performed in other regions, the distribution of precipitation is highly dependent on first-order orographic effects, which dominate regional meteorology. However, we demonstrate that topographic smoothing enhances circulation in simulated extratropical cyclones, with significant impacts on orographic precipitation. Despite precipitation reductions of 28% over the highest ranges, due to reduced ascent on windward slopes, total precipitation over the study domain increased by an average of 9% in smoothed topography experiments on account of intensified extratropical cyclone dynamics and cross-barrier moisture flux. These findings identify an important source of bias in coarse-resolution simulated precipitation in High Mountain Asia, with important implications for the application of GCMs toward projecting future hydroclimate in the region. F. Cannon L. M. V. Carvalho C. Jones J. Norris B. Bookhagen G. N. Kiladis 2015-04-24T19:56:55Z 2015-10-06T23:23:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1149 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1149 2015-04-24T19:56:55Z Atmospheric science: Extreme La Niña events to increase How climate change will impact the natural phenomenon La Niña, the counterpart of El Niño, has been unclear. In spite of uncertainty, now a study shows a large model consensus for an increasing frequency of extreme La Niña events. A. Capotondi 2012-11-09T20:37:32Z 2013-05-08T15:37:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/588 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/588 2012-11-09T20:37:32Z Can the mean structure of the tropical pycnocline affect ENSO period in coupled climate models? The dynamical link between mean state biases and dominant timescales of interannual variability is examined using the output from two state-of-the-art coupled model simulations, results from an ocean-only simulation forced with observed surface fields, and various observational data sets. The focus of this study is the relative role of the mean upper ocean density structure vs. anomalous wind forcing in controlling the spectral characteristics of tropical Pacific interannual variability. It is shown that an extensive South Pacific Convergence Zone (SPCZ) creates a potential vorticity (PV) barrier in the Southern Hemisphere similar to the one associated with the Intertropical Convergence Zone (ITCZ) in the Northern Hemisphere in both climate models. The PV barrier in the Southern Hemisphere strongly constrains the mean equatorward flow in the ocean model pycnocline, creating a "choke point" for the mean flow around 10°S. It is then examined whether the PV barrier can also limit the anomalous flow associated with mass recharge/discharge to/from the equatorial thermocline at interannual timescales. If the anomalous flow were impeded by the mean PV structure the meridional extent of the area involved in the mass recharge/discharge process would be narrower, leading to a shorter adjustment (and ENSO) timescale. Comparison of the two climate models, both of which have similarly erroneous PV structures in the southern tropical Pacific, but different interannual timescales, shows that the meridional extent of the anomalous meridional transport is primarily controlled by the latitudinal location of the wind stress curl anomalies, while the mean state bias in the Southern Hemisphere does not seem to have any significant influence. A. Capotondi 2014-01-08T20:45:49Z 2014-01-08T20:45:49Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/982 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/982 2014-01-08T20:45:49Z ENSO diversity in the NCAR CCSM4 climate model In this study we examine ENSO diversity in a 500 year control simulation of the National Center for Atmospheric Research (NCAR) Community Climate System Model version 4 (CCSM4), focusing on warm events. Standard and modified Niño3 and Niño4 indices are used to identify different event types. CCSM4 shows a rich diversity of El Niño flavors with characteristics that are comparable to what was found in observations, the SODA 2.0.2/3 ocean reanalysis, and the GFDL CM2.1 model, a climate model whose ENSO characteristics have been extensively analyzed. In agreement with previous studies available in the literature, warm events peaking in the central/western Pacific are characterized by wind stress and precipitation fields confined to the western side of the basin, and show weak or absent recharge/discharge thermocline processes. A heat budget analysis of four different El Niño flavors, peaking at different longitudes, confirms the leading role of the thermocline and zonal advective feedbacks in the Niño3 and Niño4 regions, respectively. However, the growth of events centered further west appears to be controlled by nonlinear zonal advection, a result that differs from what was found in the GFDL CM2.1 model, but that is consistent with some observational evidence. A. Capotondi 2012-11-15T17:05:00Z 2013-05-07T20:29:24Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/769 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/769 2012-11-15T17:05:00Z El Niño–Southern Oscillation Ocean Dynamics: Simulation by Coupled General Circulation Models The temporal evolution and spatial pattern of the El Niño–Southern Oscillation (ENSO) is examined in seven state-of-the-art climate models in light of simple dynamical paradigms for ENSO. In general, the simulation of ENSO has improved in the present generation of climate models, with respect to previous generations, and the evolution of the upper ocean heat content is consistent with some of the leading dynamical paradigms. Unrealistic features of the model ENSO include the spatial structure of interannual sea surface temperature (SST) variations, as well as the time evolution of interannual variability. Standard deviations of interannual SST anomalies do not maximize close to the western coast of South America, as found in nature, and extend too far west along the equator. In most of the models included in this study, ENSO events occur more frequently and more regularly than they do in nature. The comparison of two climate models with different dominant ENSO time scales, one longer and closer to observations and the other much shorter than observed, shows that the spatial structure of the anomalous wind stress during ENSO events, in particular the meridional scale of the zonal wind stress anomalies, may play a key role in setting the ENSO time scale. A. Capotondi 2013-02-11T23:16:37Z 2013-05-07T20:02:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/899 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/899 2013-02-11T23:16:37Z El Niño–Southern Oscillation ocean dynamics: Simulation by coupled general circulation models The temporal evolution and spatial pattern of the El Niño–Southern Oscillation (ENSO) is examined in seven state-of-the-art climate models in light of simple dynamical paradigms for ENSO. In general, the simulation of ENSO has improved in the present generation of climate models, with respect to previous generations, and the evolution of the upper ocean heat content is consistent with some of the leading dynamical paradigms. Unrealistic features of the model ENSO include the spatial structure of interannual sea surface temperature (SST) variations, as well as the time evolution of interannual variability. Standard deviations of interannual SST anomalies do not maximize close to the western coast of South America, as found in nature, and extend too far west along the equator. In most of the models included in this study, ENSO events occur more frequently and more regularly than they do in nature. The comparison of two climate models with different dominant ENSO time scales, one longer and closer to observations and the other much shorter than observed, shows that the spatial structure of the anomalous wind stress during ENSO events, in particular the meridional scale of the zonal wind stress anomalies, may play a key role in setting the ENSO time scale. A. Capotondi 2012-09-26T15:43:16Z 2013-05-07T19:10:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/216 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/216 2012-09-26T15:43:16Z Relationship between precipitation in the Great Plains of the United States and global SSTs: Insights from the IPCC-AR4 models Multicentury preindustrial control simulations from six of the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models are used to examine the relationship between low-frequency precipitation variations in the Great Plains (GP) region of the United States and global sea surface temperatures (SSTs). This study builds on previous work performed with atmospheric models forced by observed SSTs during the twentieth century and extends it to a coupled model context and longer time series. The climate models used in this study reproduce the precipitation climatology over the United States reasonably well, with maximum precipitation occurring in early summer, as observed. The modeled precipitation time series exhibit negative "decadal" anomalies, identified using a 5-yr running mean, of amplitude comparable to that of the twentieth-century droughts. It is found that low-frequency anomalies over the GP are part of a large-scale pattern of precipitation variations, characterized by anomalies of the same sign as in the GP region over Europe and southern South America and anomalies of opposite sign over northern South America, India, and Australia. The large-scale pattern of the precipitation anomalies is associated with global-scale atmospheric circulation changes; during wet periods in the GP, geopotential heights are raised in the tropics and high latitudes and lowered in the midlatitudes in most models, with the midlatitude jets displaced toward the equator in both hemispheres. Statistically significant correlations are found between the decadal precipitation anomalies in the GP region and tropical Pacific SSTs in all the models. The influence of other oceans (Indian and tropical and North Atlantic), which previous studies have identified as potentially important, appears to be model dependent. A. Capotondi M. A. Alexander 2012-11-08T17:16:59Z 2013-05-03T23:11:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/562 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/562 2012-11-08T17:16:59Z Enhanced upper ocean stratification with climate change in the CMIP3 models Changes in upper ocean stratification during the second half of the 21st century, relative to the second half of the 20th century, are examined in ten of the CMIP3 climate models according to the SRES-A2 scenario. The upper ocean stratification, defined here as the density difference between 200 m and the surface, is larger everywhere during the second half of the 21st century, indicative of an increasing degree of decoupling between the surface and the deeper oceans, with important consequences for many biogeochemical processes. The areas characterized by the largest stratification changes include the Arctic, the tropics, the North Atlantic, and the northeast Pacific. The increase in stratification is primarily due to the increase in surface temperature, whose influence upon density is largest in the tropical regions, and decreases with increasing latitude. The influence of salinity upon the stratification changes, while not as spatially extensive as that of temperature, is very large in the Arctic, North Atlantic and Northeast Pacific. Salinity also significantly contributes to the density decrease near the surface in the western tropical Pacific, but counteracts the negative influence of temperature upon density in the tropical Atlantic. A. Capotondi M. A. Alexander N. A. Bond E. N. Curchitser 2012-11-06T18:37:18Z 2013-05-13T15:42:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/489 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/489 2012-11-06T18:37:18Z Anatomy and decadal evolution of the Pacific Subtropical-Tropical Cells (STCs) A. Capotondi M. A. Alexander C. Deser M. J. McPhaden 2012-10-01T16:57:19Z 2013-04-24T20:32:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/281 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/281 2012-10-01T16:57:19Z Low-frequency variability in the Gulf of Alaska from coarse and eddy-permitting ocean models An eddy-permitting ocean model of the northeast Pacific is used to examine the ocean adjustment to changing wind forcing in the Gulf of Alaska (GOA) at interannual-to-decadal timescales. It is found that the adjustment of the ocean model in the presence of mesoscale eddies is similar to that obtained with coarse-resolution models. Local Ekman pumping plays a key role in forcing pycnocline depth variability and, to a lesser degree, sea surface height (SSH) variability in the center of the Alaska gyre and in some areas of the eastern and northern GOA. Westward Rossby wave propagation is evident in the SSH field along some latitudes but is less noticeable in the pycnocline depth field. Differences between SSH and pycnocline depth are also found when considering their relationship with the local forcing and leading modes of climate variability in the northeast Pacific. In the central GOA pycnocline depth variations are more clearly related to changes in the local Ekman pumping than SSH. While SSH is marginally correlated with both Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) indices, the pycnocline depth evolution is primarily related to NPGO variability. The intensity of the mesoscale eddy field increases with increasing circulation strength. The eddy field is generally more energetic after the 1976–1977 climate regime shift, when the gyre circulation intensified. In the western basin, where eddies primarily originate from intrinsic instabilities of the flow, variations in eddy kinetic energy are statistically significant correlated with the PDO index, indicating that eddy statistics may be inferred, to some degree, from the characteristics of the large-scale flow. A. Capotondi V. Combes M. A. Alexander E. Di Lorenzo A. J. Miller 2012-11-06T18:29:47Z 2013-05-13T15:42:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/488 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/488 2012-11-06T18:29:47Z Low-frequency pycnocline variability in the northeast Pacific The output from an ocean general circulation model (OGCM) driven by observed surface forcing is used in conjunction with simpler dynamical models to examine the physical mechanisms responsible for interannual to interdecadal pycnocline variability in the northeast Pacific Ocean during 1958–97, a period that includes the 1976–77 climate shift. After 1977 the pycnocline deepened in a broad band along the coast and shoaled in the central part of the Gulf of Alaska. The changes in pycnocline depth diagnosed from the model are in agreement with the pycnocline depth changes observed at two ocean stations in different areas of the Gulf of Alaska. A simple Ekman pumping model with linear damping explains a large fraction of pycnocline variability in the OGCM. The fit of the simple model to the OGCM is maximized in the central part of the Gulf of Alaska, where the pycnocline variability produced by the simple model can account for 70%–90% of the pycnocline depth variance in the OGCM. Evidence of westward-propagating Rossby waves is found in the OGCM, but they are not the dominant signal. On the contrary, large-scale pycnocline depth anomalies have primarily a standing character, thus explaining the success of the local Ekman pumping model. The agreement between the Ekman pumping model and OGCM deteriorates in a large band along the coast, where propagating disturbances within the pycnocline, due to either mean flow advection or boundary waves, appear to play an important role in pycnocline variability. Coastal propagation of pycnocline depth anomalies is especially relevant in the western part of the Gulf of Alaska, where local Ekman pumping-induced changes are anticorrelated with the OGCM pycnocline depth variations. The pycnocline depth changes associated with the 1976–77 climate regime shift do not seem to be consistent with Sverdrup dynamics, raising questions about the nature of the adjustment of the Alaska Gyre to low-frequency wind stress variability. A. Capotondi C. Deser A. J. Miller 2014-01-09T00:58:12Z 2014-01-09T00:58:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1011 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1011 2014-01-09T00:58:12Z Challenges in understanding and modeling ENSO Some new exciting directions in ENSO research explore inter-event differences in spatial patterns, teleconnections and impacts, asymmetries between warm and cold phases, and the role of extra-tropical regions in triggering ENSO events. However, large uncertainties remain regarding ENSO projections. A. Capotondi E. Guilyardi B. Kirtman 2015-04-24T19:40:15Z 2015-10-06T23:32:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1151 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1151 2015-04-24T19:40:15Z Climate model biases and El Niño Southern Oscillation (ENSO) simulation N/A A. Capotondi Y. Ham A. Wittenberg J. Kug 2017-05-05T20:39:08Z 2017-05-05T20:39:23Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1504 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1504 2017-05-05T20:39:08Z ENSO diversity and its implications for US West coast marine ecosystems N/A A. Capotondi K. Karnauskas A. Miller A. Subramanian 2016-04-11T21:13:33Z 2016-04-11T21:13:33Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1316 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1316 2016-04-11T21:13:33Z Optimal precursors of different types of ENSO events Not all El Niño–Southern Oscillation (ENSO) events are the same. Their global impacts can differ substantially depending on whether the associated sea surface temperature (SST) anomalies are stronger in the central Pacific (CP) or the eastern Pacific (EP). The predictability of such differences is therefore of interest. In this study, the optimal two-season precursors of different ENSO types are investigated in a linear inverse modeling framework using observational SST and thermocline depth data for 1958–2007. It is shown that different SST precursor types alone do not favor the generation of different ENSO types. However, initial subsurface conditions characterized by a deeper thermocline in the eastern Pacific and a shallower thermocline in the central Pacific favor the generation of EP-type events, while a shallower thermocline in the east and a deeper thermocline in the central/western Pacific are conducive to CP-type events. The predictability of different ENSO types thus depends importantly on initial subsurface conditions. A. Capotondi P. D. Sardeshmukh 2014-01-09T00:54:36Z 2014-01-09T00:54:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1009 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1009 2014-01-09T00:54:36Z ENSO diversity in climate models N/A A. Capotondi A. Wittenberg 2012-09-23T01:54:25Z 2013-05-10T20:02:10Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/111 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/111 2012-09-23T01:54:25Z Spatial and temporal structure of tropical Pacific interannual variability in 20th Century coupled simulations Tropical Pacific interannual variability is examined in nine state-of-the-art coupled climate models, and compared with observations and ocean analyses data sets, the primary focus being on the spatial structure and spectral characteristics of El Niño-Southern Oscillation (ENSO). The spatial patterns of interannual sea surface temperature (SST) anomalies from the coupled models are characterized by maximum variations displaced from the coast of South America, and generally extending too far west with respect to observations. Thermocline variability is characterized by dominant modes that are qualitatively similar in all the models, and consistent with the "recharge oscillator" paradigm for ENSO. The meridional scale of the thermocline depth anomalies is generally narrower than observed, a result that can be related to the pattern of zonal wind stress perturbations in the central-western equatorial Pacific. The wind stress response to eastern equatorial Pacific SST anomalies in the models is narrower and displaced further west than observed. The meridional scale of the wind stress can affect the amount of warm water involved in the recharge/discharge of the equatorial thermocline, while the longitudinal location of the wind stress anomalies can influence the advection of the mean zonal temperature gradient by the anomalous zonal currents, a process that may favor the growth and longer duration of ENSO events when the wind stress perturbations are displaced eastwards. Thus, both discrepancies of the wind stress anomaly patterns in the coupled models with respect to observations (narrow meridional extent, and westward displacement along the equator) may be responsible for the ENSO timescale being shorter in the models than in observations. The examination of the leading advective processes in the SST tendency equation indicates that vertical advection of temperature anomalies tends to favor ENSO growth in all the CGCMs, but at a smaller rate than in observations. In some models it can also promote a phase transition. Longer periods tend to be associated with thermocline and advective feedbacks that are in phase with the SST anomalies, while advective tendencies that lead the SST anomalies by a quarter cycle favor ENSO transitions, thus leading to a shorter period. A. Capotondi A. Wittenberg S. Masina 2015-04-24T19:56:40Z 2015-10-06T23:27:05Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1150 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1150 2015-04-24T19:56:40Z Understanding ENSO diversity The El Niño Southern Oscillation (ENSO) is a naturally occurring mode of tropical Pacific variability, with global impacts on society and natural ecosystems. While it has long been known that El Niño events display a diverse range of amplitudes, triggers, spatial patterns, and life cycles, the realization that ENSO's impacts can be highly sensitive to this event-to-event diversity is driving a renewed interest in the subject. This paper surveys our current state of knowledge of ENSO diversity, identifies key gaps in understanding, and outlines some promising future research directions. A. Capotondi A. Wittenberg M. Newman et al. 2014-01-13T19:15:31Z 2014-01-13T19:29:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1039 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1039 2014-01-13T19:15:31Z Sensitivity of southern California wind energy to turbine characteristics Using output from a high-resolution meteorological simulation, we evaluate the sensitivity of southern California wind energy generation to variations in key characteristics of current wind turbines. These characteristics include hub height, rotor diameter and rated power, and depend on turbine make and model. They shape the turbine's power curve and thus have large implications for the energy generation capacity of wind farms. For each characteristic, we find complex and substantial geographical variations in the sensitivity of energy generation. However, the sensitivity associated with each characteristic can be predicted by a single corresponding climate statistic, greatly simplifying understanding of the relationship between climate and turbine optimization for energy production. In the case of the sensitivity to rotor diameter, the change in energy output per unit change in rotor diameter at any location is directly proportional to the weighted average wind speed between the cut-in speed and the rated speed. The sensitivity to rated power variations is likewise captured by the percent of the wind speed distribution between the turbines rated and cut-out speeds. Finally, the sensitivity to hub height is proportional to lower atmospheric wind shear. Using a wind turbine component cost model, we also evaluate energy output increase per dollar investment in each turbine characteristic. We find that rotor diameter increases typically provide a much larger wind energy boost per dollar invested, although there are some zones where investment in the other two characteristics is competitive. Our study underscores the need for joint analysis of regional climate, turbine engineering and economic modeling to optimize wind energy production. Copyright © 2012 John Wiley & Sons, Ltd. S. B. Capps A. Hall M. Hughes 2016-04-11T21:16:19Z 2016-04-11T21:16:19Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1317 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1317 2016-04-11T21:16:19Z Toward Quantifying the Increasing Role of Oceanic Heat in Sea Ice Loss in the New Arctic The loss of Arctic sea ice has emerged as a leading signal of global warming. This, together with acknowledged impacts on other components of the Earth system, has led to the term "the new Arctic." Global coupled climate models predict that ice loss will continue through the twenty-first century, with implications for governance, economics, security, and global weather. A wide range in model projections reflects the complex, highly coupled interactions between the polar atmosphere, ocean, and cryosphere, including teleconnections to lower latitudes. This paper summarizes our present understanding of how heat reaches the ice base from the original sources—inflows of Atlantic and Pacific Water, river discharge, and summer sensible heat and shortwave radiative fluxes at the ocean/ice surface—and speculates on how such processes may change in the new Arctic. The complexity of the coupled Arctic system, and the logistic and technological challenges of working in the Arctic Ocean, require a coordinated interdisciplinary and international program that will not only improve understanding of this critical component of global climate but will also provide opportunities to develop human resources with the skills required to tackle related problems in complex climate systems. We propose a research strategy with components that include 1) improved mapping of the upper- and middepth Arctic Ocean, 2) enhanced quantification of important process, 3) expanded long-term monitoring at key heat-flux locations, and 4) development of numerical capabilities that focus on parameterization of heat-flux mechanisms and their interactions. E. Carmack I. Polyakov L. Padman . . . P. O. G. Persson et al. 2014-07-15T19:19:16Z 2014-07-15T19:23:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1058 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1058 2014-07-15T19:19:16Z Wyoming Basin Rapid Ecoregional Assessment Work Plan The overall goal of the Rapid Ecoregional Assessments (REAs) being conducted for the Bureau of Land Management (BLM) is to provide information that supports regional planning and analysis for the management of ecological resources. The REA provides an assessment of baseline ecological conditions, an evaluation of current risks from drivers of ecosystem change, and a predictive capacity for evaluating future risks. The REA also may be used for identifying priority areas for conservation or restoration and for assessing the cumulative effects of a variety of land uses. There are several components of the REAs. Management Questions, developed by the BLM and partners for the ecoregion, identify the information needed for addressing land-management responsibilities. Conservation Elements represent regionally significant aquatic and terrestrial species and communities that are to be conserved and (or) restored. The REA also will evaluate major drivers of ecosystem change (Change Agents) currently affecting or likely to affect the status of Conservation Elements. We selected 8 major biomes and 19 species or species assemblages to be included as Conservation Elements. We will address the four primary Change Agents—development, fire, invasive species, and climate change—required for the REA. The purpose of the work plan for the Wyoming Basin REA is to document the selection process for, and final list of, Management Questions, Conservation Elements, and Change Agents. The work plan also presents the overall assessment framework that will be used to assess the status of Conservation Elements and answer Management Questions. N. B. Carr S. L. Garman A. Walters A. J. Ray et al. 2012-12-21T20:32:06Z 2013-05-03T23:16:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/845 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/845 2012-12-21T20:32:06Z Precipitation Characteristics of the South American Monsoon System Derived from Multiple Datasets The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation during the austral summer. This study compares several statistical properties of daily gridded precipitation from different data (1998–2008): 1) Physical Sciences Division (PSD), Earth System Research Laboratory [1.0° and 2.5° latitude (lat)/longitude (lon)]; 2) Global Precipitation Climatology Project (GPCP; 1° lat/lon); 3) Climate Prediction Center (CPC) unified gauge (CPC-uni) (0.5° lat/lon); 4) NCEP Climate Forecast System Reanalysis (CFSR) (0.5° lat/lon); 5) NASA Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis (0.5° lat/0.3° lon); and 6) Tropical Rainfall Measuring Mission (TRMM) 3B42 V6 data (0.25° lat/lon). The same statistical analyses are applied to data in 1) a common 2.5° lat/lon grid and 2) in the original resolutions of the datasets. All datasets consistently represent the large-scale patterns of the SAMS. The onset, demise, and duration of SAMS are consistent among PSD, GPCP, CPC-uni, and TRMM datasets, whereas CFSR and MERRA seem to have problems in capturing the correct timing of SAMS. Spectral analyses show that intraseasonal variance is somewhat similar in the six datasets. Moreover, differences in spatial patterns of mean precipitation are small among PSD, GPCP, CPC-uni, and TRMM data, while some discrepancies are found in CFSR and MERRA relative to the other datasets. Fitting of gamma frequency distributions to daily precipitation shows differences in the parameters that characterize the shape, scale, and tails of the frequency distributions. This suggests that significant uncertainties exist in the characterization of extreme precipitation, an issue that is highly important in the context of climate variability and change in South America. L. M. V. Carvalho C. Jones A. N. D. Posadas . . . B. Liebmann 2012-11-13T17:32:42Z 2013-05-02T16:27:45Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/616 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/616 2012-11-13T17:32:42Z The South American Monsoon System and the 1970s climate transition The South American Monsoon System (SAMS) is characterised by intense convective activity and precipitation during austral summer. This study investigates changes in the onset, demise and duration of SAMS during 1948–2008. The results show a significant change in these characteristics in the early 1970s. Onset becomes steadily earlier from 1948 to early 1970s and has occurred earlier than 23–27 October after 1972–1973. Demise dates have remained later than 21–25 April after the mid-to-late 1970s. SAMS duration shows a statistical changepoint in the summer of 1971–1972 such that the mean duration was ∼170 days (1948–1972) and 195 days (1972–1982). Vertically integrated moisture flux is used to diagnose changes in mean state and reveal statistically significant increases over South America after 1971–1972. Copyright © 2010 Royal Meteorological Society L. M. V. Carvalho C. Jones A. E. Silva B. Liebmann P. L. Silva Dias 2012-11-13T17:34:43Z 2013-05-02T16:28:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/617 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/617 2012-11-13T17:34:43Z Moisture transport and intraseasonal variability in the South America monsoon system This paper examines moisture transport on intraseasonal timescales over the continent and over the South Atlantic convergence zone (SACZ) during the South America (SA) summer monsoon. Combined Empirical Orthogonal Function analysis (EOFc) of Global Precipitation Climatology Project pentad precipitation, specific humidity, air temperature, zonal and meridional winds at 850 hPa (NCEP/NCAR reanalysis) are performed to identify the large-scale variability of the South America monsoon system and the SACZ. The first EOFc was used as a large-scale index for the South American monsoon (LISAM), whereas the second EOFc characterized the SACZ. LISAM (SACZ) index showed spectral variance on 30–90 (15–20) days and were both band filtered (10–100 days). Intraseasonal wet anomalies were defined when LISAM and SACZ anomalies were above the 75th percentile of their respective distribution. LISAM and SACZ wet events were examined independently of each other and when they occur simultaneously. LISAM wet events were observed with the amplification of wave activity in the Northern Hemisphere and the enhancement of northwesterly cross-equatorial moisture transport over tropical continental SA. Enhanced SACZ was observed with moisture transport from the extratropics of the Southern Hemisphere. Simultaneous LISAM and SACZ wet events are associated with cross-equatorial moisture transport along with moisture transport from Subtropical Southwestern Atlantic. L. M. V. Carvalho A. E. Silva C. Jones B. Liebmann P. L. Silva Dias H. R. Rocha 2017-07-07T20:53:43Z 2017-07-07T20:53:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1519 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1519 2017-07-07T20:53:43Z Development of the Regional Arctic System Model (RASM): Near-Surface Atmospheric Climate Sensitivity The near-surface climate, including the atmosphere, ocean, sea ice, and land state and fluxes, in the initial version of the Regional Arctic System Model (RASM) are presented. The sensitivity of the RASM near-surface climate to changes in atmosphere, ocean, and sea ice parameters and physics is evaluated in four simulations. The near-surface atmospheric circulation is well simulated in all four RASM simulations but biases in surface temperature are caused by biases in downward surface radiative fluxes. Errors in radiative fluxes are due to biases in simulated clouds with different versions of RASM simulating either too much or too little cloud radiative impact over open ocean regions and all versions simulating too little cloud radiative impact over land areas. Cold surface temperature biases in the central Arctic in winter are likely due to too few or too radiatively thin clouds. The precipitation simulated by RASM is sensitive to changes in evaporation that were linked to sea surface temperature biases. Future work will explore changes in model microphysics aimed at minimizing the cloud and radiation biases identified in this work. J. J. Cassano A. DuVivier M. Hughes M. Seefeldt M. Brunke A. Craig B. Fisel W. Gutowski J. Hamman M. Higgins W. Maslowski B. Nijssen R. Osinski X. Zeng 2012-10-15T23:23:29Z 2013-05-07T17:59:10Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/295 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/295 2012-10-15T23:23:29Z Investigating the Impact of Reemerging Sea Surface Temperature Anomalies on the Winter Atmospheric Circulation over the North Atlantic Extratropical SSTs can be influenced by the "reemergence mechanism," whereby thermal anomalies in the deep winter mixed layer persist at depth through summer and are then reentrained into the mixed layer in the following winter. The impact of reemergence in the North Atlantic Ocean (NAO) upon the climate system is investigated using an atmospheric general circulation model coupled to a mixed layer ocean/thermodynamic sea ice model. The dominant pattern of thermal anomalies below the mixed layer in summer in a 150-yr control integration is associated with the North Atlantic SST tripole forced by the NAO in the previous winter as indicated by singular value decomposition (SVD). To isolate the reemerging signal, two additional 60-member ensemble experiments were conducted in which temperature anomalies below 40 m obtained from the SVD analysis are added to or subtracted from the control integration. The reemerging signal, given by the mean difference between the two 60-member ensembles, causes the SST anomaly tripole to recur, beginning in fall, amplifying through January, and persisting through the following spring. The atmospheric response to these SST anomalies resembles the circulation that created them the previous winter but with reduced amplitude (10–20 m at 500 mb per °C), modestly enhancing the winter-to-winter persistence of the NAO. Changes in the transient eddies and their interactions with the mean flow contribute to the large-scale equivalent barotropic response throughout the troposphere. The latter can also be attributed to the change in occurrence of intrinsic weather regimes. C. Cassou C. Deser M. A. Alexander 2015-10-07T14:33:50Z 2015-10-07T14:33:50Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1225 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1225 2015-10-07T14:33:50Z The annual cycle of snowfall at Summit, Greenland While snow accumulation over central Greenland has been extensively studied, interannual variability of snowfall in the region is not well understood due to a dearth of observations. The Integrated Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS) project at Summit, Greenland, offers a unique, ground-based opportunity to study precipitation in central Greenland where the surface mass balance is positive. Combining data from a Precipitation Occurrence Sensor System (POSS), Millimeter-wavelength Cloud Radar (MMCR), and snow stake field, the annual cycle of precipitation at Summit is examined. Average daily snowfall is higher by a factor of 3 from June to October compared to November to May, while surface height change is only higher by 15% during the same timeframes. This reduced variability in surface height is explained by the seasonally varying nature of latent heat flux, compaction, and wind contributions. The ICECAPS remote sensors and stake field measurements do not agree as far as total annual water equivalent. This discrepancy is likely due to a low bias in the POSS and MMCR snowfall retrievals for Summit. To further examine the seasonal cycle, snowfall measurements by the POSS were linked to local meteorological parameters, including wind direction, liquid water path (LWP), 2 m temperature, and precipitable water vapor. An observed wind direction and moisture dependence are consistent with snowfall being linked to pulses of moist air that originate over nearby, ice-free ocean, a resource that becomes more readily available in summertime as the winter sea ice retreats. LWP is shown to have little relationship to snowfall, indicating that ice-phase precipitation processes are quite important for snowfall at Summit. B. B. Castellani M. D. Shupe D. R. Hudak B. E. Sheppard 2014-07-15T19:23:06Z 2014-07-15T19:23:06Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1060 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1060 2014-07-15T19:23:06Z Comparison of diurnal warming estimates from unpumped Argo data and SEVIRI satellite observations Estimates of diurnal warming at the ocean surface from modified Argo floats providing unpumped measurements of temperature up to the surface are compared against collocated satellite-derived values from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) flying on the METEOSAT-9 Second Generation (MSG) geostationary satellite. The amplitude of diurnal warming is computed from the difference between subskin and foundation temperature estimates derived independently from the Argo and SEVIRI data. The results demonstrate remarkable consistency between the observations, lending support for both products and the associated methodologies, particularly for the estimation of the foundation temperature. Individual subskin values agree to within an absolute mean difference of ≤ 0.1 K and standard deviations of the differences are < 0.4 K. Statistics for comparison of the foundation temperatures are similar. Differences between the corresponding derived estimates of diurnal warming have negligible bias and standard deviations < 0.25 K. The strong agreement of the diurnal warming estimates exists even when excluding nearly isothermal profiles, suggesting the differences are robust to small spatial offsets and point-to-pixel differences. The results particularly support the ability of the modified Argo floats to provide reliable, and highly valuable, measurements of the near-surface temperature, helping to argue for more modified floats. Moreover, the results suggest that the unpumped Argo data has the potential to provide an independent estimate of the foundation temperature for validation of SST analyses. The method for estimating the foundation temperature from SEVIRI represents a good compromise between data coverage and influences of cloud contamination and nighttime cooling. S. L. Castro G. A. Wick J. J. H. Buck 2012-05-04T17:05:41Z 2013-05-03T17:11:34Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/26 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/26 2012-05-04T17:05:41Z Evaluation of the relative performance of sea surface temperature measurements from different types of drifting and moored buoys using satellite-derived reference products Sea surface temperature (SST) measurements from drifting and moored buoys have been used extensively to validate satellite SST products. Previous efforts explored overall uncertainties in the buoy measurements, but did not quantify differences in the performance of different buoy types. Here, drifting and moored buoys stratified into open-ocean and coastal, were evaluated by manufacturer (drifters) and buoy program (moorings) to identify significant deviations in their suitability for satellite validation. Biases and standard deviations were computed for differences between the buoy SST measurements and two satellite references: the Advanced Microwave Scanning Radiometer SST product from Remote Sensing Systems and the U.S. Naval Oceanographic Office K10 analysis. No significant differences were found among the various drifting and tropical moored buoys, regardless of the manufacturer/program. The largest deviations were observed for the non-tropical moored buoys possibly in part due to calibration differences. In general, coastal buoys exhibited greater standard deviations associated with increased physical variability within the coastal regions. Tropical moored buoys showed smaller standard deviations than for the drifters resulting from better quality measurements or reduced variability in the tropics. Large deviations between the coastal moorings and the SST references appeared linked to coastal currents with upwelling, rather than buoy performance. Coastal moorings provided sampling of small-scale coastal variability, not resolved in satellite products, offering the potential for improving poorly parameterized coastal SSTs. Differences due to diurnal warming were largely eliminated by constraining collocations between the satellite and the buoy to ±1 h. Overall, most buoy types appear suitable for satellite SST validation. S. L. Castro G. A. Wick W. J. Emery 2012-11-09T20:44:56Z 2013-05-08T15:38:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/590 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/590 2012-11-09T20:44:56Z Error characterization of infrared and microwave satellite sea surface temperature products for merging and analysis The complementary nature of infrared and microwave sea surface temperature (SST) products provides opportunities for merging the data, but significant differences among the products must first be understood and characterized. This paper presents a method for specifying the uncertainty in existing infrared and microwave SST products in terms of available satellite-derived parameters, explores which environmental and sensor parameters contribute most to the errors, and determines if the derived uncertainty estimates can enable significant reductions in the differences among the SST products. Collocations among the satellite retrievals and SST measurements from buoys are used to derive the error estimates. Simple multidimensional lookup tables expressing the expected bias and standard deviation of individual retrievals as functions of various combinations of parameters provide an effective characterization of the uncertainty suitable for operational applications. Bias adjustments derived from the satellite zenith angle, 11–12 μm brightness temperature difference, and SST for the infrared, and wind speed, water vapor content, and SST for the microwave products significantly reduce the variability of differences both between the satellite products and with buoy observations. Further improvements are possible through inclusion of additional independent corrections based on the climatological SST anomaly and aerosol optical depth. These corrections reduce the monthly rms difference between the products by as much as 42% and reduce differences with independent buoys by as much as 10%. The largest individual corrections are to the infrared data in regions of low SST, but the microwave corrections are more geographically distributed and affect more retrievals. S. L. Castro G. A. Wick D. L. Jackson W. J. Emery 2012-11-15T17:07:34Z 2013-05-08T14:58:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/771 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/771 2012-11-15T17:07:34Z The impact of measurement uncertainty and spatial variability on the accuracy of skin and subsurface regression-based sea surface temperature algorithms An ongoing limitation of common regression-based infrared (IR) satellite sea surface temperature (SST) algorithms has been the lack of sufficient in situ skin temperature measurements for derivation of the algorithm coefficients. Since IR brightness temperatures respond to the skin temperature, use of the more numerous subsurface observations to tune the algorithms introduces uncertainty into the resulting SST products. Coincident in situ skin and subsurface SST measurements from three years of cruises are used to derive parallel skin and subsurface multichannel SST (MCSST)-type regression algorithms to determine the extent to which improved accuracy can be obtained using the skin measurements. Through use of only coincident measurements, the advantage offered by the greater volume of available subsurface observations is eliminated. Surprisingly, we find no accuracy improvement using skin SST algorithms relative to algorithms derived from the research-grade ship-borne subsurface temperature measurements used in our analysis. However, better accuracy was found relative to algorithms derived from subsurface observations whose accuracy was degraded to that of buoys. The results are robust with regard to satellite resolution, collocation criteria, geographical regions, and time of day. The accuracy differences are found to be generally consistent with the effects of: (1) increased measurement uncertainty of radiometric measurements relative to research-grade subsurface observations, and (2) differences in spatial variability between the skin SST and temperature-at-depth. The subsurface algorithms are regenerated after degrading the subsurface measurements by adding increasing levels of Gaussian white noise to determine the amplitude of the additional variability required to ensure equal accuracy between the skin and subsurface products. The required supplemental noise ranges between 0.10 and 0.17 K for all data combined and generally decreases with tighter collocation windows and higher-resolution satellite observations. Variogram analysis and filtering of the in situ measurements suggest that differences in measurement uncertainty between the infrared radiometers and the subsurface sensors can explain 0.07–0.10 K of the required noise, while differences in spatial variability with depth can account for up to 0.07–0.10 K of the residual noise. A key consequence is that spatial averages of the skin temperature over satellite footprints of 2 km or more, while potentially biased in the mean, may exhibit less variance relative to point samples of the subsurface temperature than to the actual radiometric skin temperature. S. L. Castro G. A. Wick P. J. Minnett A. T. Jessup W. J. Emery 2017-01-03T16:47:50Z 2017-01-03T16:47:50Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1451 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1451 2017-01-03T16:47:50Z Validation of satellite sea surface temperature analyses in the Beaufort Sea using UpTempO buoys Many different blended sea surface temperature (SST) analyses are currently available and exhibit significant differences in the high latitude regions. It is challenging for users to determine which of these products is most accurate and best suited for their applications. Nine different SST analyses and two single sensor satellite products are compared with independent observations from Upper Temperature of the polar Oceans (UpTempO) buoys deployed in the Beaufort Sea in 2012 and 2013 during the Marginal Ice Zone Processes Experiment (MIZOPEX). The relative skill of the different SST products is evaluated using a combination of Taylor diagrams and two different verification scores that weight different statistical measures. Skill thresholds based on satellite accuracy requirements are chosen to map products with similar performance into three discrete skill categories: excellent, good, and poor. Results are presented for three subsets of the buoys corresponding to different regimes: coastal waters, northerly waters, and extreme weather. The presence of strong thermal gradients and cloudiness posed problems for the SST products, while in more homogeneous regions the performance was improved and more similar among products. The impact of variations in the ice mask between the SST products was mostly inconsequential. While the relative performance of the analyses varied with regime, overall, the best performing analyses for this region and period included the NOAA Optimal Interpolation SST (OISST), the Canadian Meteorological Centre (CMC) SST, and the Group for High Resolution SST (GHRSST) Multi-Product Ensemble (GMPE). S. L. Castro G. A. Wick M. Steele 2012-12-21T20:42:03Z 2013-05-07T18:43:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/846 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/846 2012-12-21T20:42:03Z A Comparison of Snow Depth on Sea Ice Retrievals Using Airborne Altimeters and an AMSR-E Simulator A comparison of snow depths on sea ice was made using airborne altimeters and an Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) simulator. The data were collected during the March 2006 National Aeronautics and Space Administration (NASA) Arctic field campaign utilizing the NASA P-3B aircraft. The campaign consisted of an initial series of coordinated surface and aircraft measurements over Elson Lagoon, Alaska and adjacent seas followed by a series of large-scale (100 km × 50 km) coordinated aircraft and AMSR-E snow depth measurements over portions of the Chukchi and Beaufort seas. This paper focuses on the latter part of the campaign. The P-3B aircraft carried the University of Colorado Polarimetric Scanning Radiometer (PSR-A), the NASA Wallops Airborne Topographic Mapper (ATM) lidar altimeter, and the University of Kansas Delay-Doppler (D2P) radar altimeter. The PSR-A was used as an AMSR-E simulator, whereas the ATM and D2P altimeters were used in combination to provide an independent estimate of snow depth. Results of a comparison between the altimeter-derived snow depths and the equivalent AMSR-E snow depths using PSR-A brightness temperatures calibrated relative to AMSR-E are presented. Data collected over a frozen coastal polynya were used to intercalibrate the ATM and D2P altimeters before estimating an altimeter snow depth. Results show that the mean difference between the PSR and altimeter snow depths is -2.4 cm (PSR minus altimeter) with a standard deviation of 7.7 cm. The RMS difference is 8.0 cm. The overall correlation between the two snow depth data sets is 0.59. D. J. Cavalieri S. Spring T. Markus . . . A. J. Gasiewski et al. 2013-08-13T17:56:44Z 2013-08-13T17:56:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/940 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/940 2013-08-13T17:56:44Z Chapter 6. Future Climate: Projected Average D. R. Cayan M. Tyree E. Kunkel C. Castro A. Gershunov J. Barsugli A. J. Ray et al. 2013-01-31T21:43:00Z 2013-04-24T17:41:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/883 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/883 2013-01-31T21:43:00Z Ubiquitous low-level liquid-containing Arctic clouds: New observations and climate model constraints from CALIPSO-GOCCP Ground-based observations show that persistent liquid-containing Arctic clouds occur frequently and have a dominant influence on Arctic surface radiative fluxes. Yet, without a hemispheric multi-year perspective, the climate relevance of these intriguing Arctic cloud observations was previously unknown. In this study, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) observations are used to document cloud phase over the Arctic basin (60–82°N) during a five-year period (2006–2011). Over Arctic ocean-covered areas, low-level liquid-containing clouds are prevalent in all seasons, especially in Fall. These new CALIPSO observations provide a unique and climate-relevant constraint on Arctic cloud processes. Evaluation of one climate model using a lidar simulator suggests a lack of liquid-containing Arctic clouds contributes to a lack of "radiatively opaque" states. The surface radiation biases found in this one model are found in multiple models, highlighting the need for improved modeling of Arctic cloud phase. G. Cesana J. E. Kay H. Chepfer J. M. English G. de Boer 2015-10-07T14:40:46Z 2015-10-07T14:40:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1223 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1223 2015-10-07T14:40:46Z Automated rain rate estimates using the Ka-band ARM zenith radar (KAZR) The use of millimeter wavelength radars for probing precipitation has recently gained interest. However, estimation of precipitation variables is not straightforward due to strong signal attenuation, radar receiver saturation, antenna wet radome effects and natural microphysical variability. Here, an automated algorithm is developed for routinely retrieving rain rates from the profiling Ka-band (35-GHz) ARM (Atmospheric Radiation Measurement) zenith radars (KAZR). A 1-dimensional, simple, steady state microphysical model is used to estimate impacts of microphysical processes and attenuation on the profiles of radar observables at 35-GHz and thus provide criteria for identifying situations when attenuation or microphysical processes dominate KAZR observations. KAZR observations are also screened for signal saturation and wet radome effects. The algorithm is implemented in two steps: high rain rates are retrieved by using the amount of attenuation in rain layers, while low rain rates are retrieved from the reflectivity–rain rate (Ze–R) relation. Observations collected by the KAZR, rain gauge, disdrometer and scanning precipitating radars during the DYNAMO/AMIE field campaign at the Gan Island of the tropical Indian Ocean are used to validate the proposed approach. The differences in the rain accumulation from the proposed algorithm are quantified. The results indicate that the proposed algorithm has a potential for deriving continuous rain rate statistics in the tropics. A. Chandra C. Zhang P. Kollias S. Y. Matrosov 2013-01-16T16:18:41Z 2013-05-03T23:10:13Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/872 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/872 2013-01-16T16:18:41Z Concepts and principles of rainfall estimation from radar: Multi-sensor environment and data fusion Rainfall estimation has been pursued nearly since the dawn of civilization. It is also one of the most commonly used applications of modern, meteorological radars in most operational systems. Multi sensor approaches have made great strides in addressing the rainfall estimation problem through better sensor calibration and improved integration of observations at scales spanning many orders of magnitude such as radar, satellite and rain gauges. Data fusion techniques have demonstrated advantages in precipitation retrievals, especially for radar observations at attenuated frequencies. Data fusion has also shown benefits in merging data from multiple radars, as well as radars and satellites. This paper describes essential concepts of multi sensor rainfall estimation with a radar focus. Validation concepts for remote estimation of rainfall are also presented. Examples of data fusion and validation are illustrated through rainfall estimate comparisons between gauge and radar networks. V. Chandrasekar R. Cifelli 2012-10-15T23:23:36Z 2013-05-07T17:26:52Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/296 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/296 2012-10-15T23:23:36Z A New Look at Stratospheric Sudden Warmings Part II: Evaluation of Numerical Model Simulations The simulation of major midwinter stratospheric sudden warmings (SSWs) in six stratosphere-resolving general circulation models (GCMs) is examined. The GCMs are compared to a new climatology of SSWs, based on the dynamical characteristics of the events. First, the number, type, and temporal distribution of SSW events are evaluated. Most of the models show a lower frequency of SSW events than the climatology, which has a mean frequency of 6.0 SSWs per decade. Statistical tests show that three of the six models produce significantly fewer SSWs than the climatology, between 1.0 and 2.6 SSWs per decade. Second, four process-based diagnostics are calculated for all of the SSW events in each model. It is found that SSWs in the GCMs compare favorably with dynamical benchmarks for SSW established in the first part of the study. These results indicate that GCMs are capable of quite accurately simulating the dynamics required to produce SSWs, but with lower frequency than the climatology. Further dynamical diagnostics hint that, in at least one case, this is due to a lack of meridional heat flux in the lower stratosphere. Even though the SSWs simulated by most GCMs are dynamically realistic when compared to the NCEP–NCAR reanalysis, the reasons for the relative paucity of SSWs in GCMs remains an important and open question. A. J. Charlton L. M. Polvani J. Perlwitz F. Sassi E. Manzini K. Shibata S. Pawson J. E. Nielsen D. Rind 2012-11-15T18:11:43Z 2013-05-08T14:56:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/773 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/773 2012-11-15T18:11:43Z Beam scintillations for ground-to-space propagation. Part 2: Gaussian beam scintillation On the basis of the analytic techniques presented in the first of these two companion papers [ J. Opt. Soc. Am. A 27, 2169 (2010) ] we present the complete asymptotic analysis of the axial beam scintillation index for coherent Gaussian beams on the ground-to-space propagation paths. The ratio of turbulence layer thickness to overall propagation path length contributes an additional small parameter to the analysis. We show that it is possible to use three dimensionless parameters to describe the problem and that the general arrangement of the asymptotic regions established in our earlier work [ Waves Random Media 4, 243 (1994) ]) is preserved. We find that on a slant propagation path, collimated beams can experience the unusual double-scattering-dominated scintillation found originally for focused beams. M. I. Charnotskii 2012-11-15T18:05:13Z 2013-05-08T14:56:37Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/772 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/772 2012-11-15T18:05:13Z Beam scintillations for ground-to-space propagation. Part I: Path integrals and analytic techniques We extend our theory of on-axis beam scintillations [Waves Random Media 4, 243 (1994)] for the case of propagation on slant turbulent paths, where turbulence is concentrated in a relatively thin layer near the transmitter. Our technique is based on the parabolic equation for optical wave propagation and the Markov approximation for the calculation of statistical moments of beam intensity. This first of two companion papers presents the details of the path integral formulation of the solution for the fourth-order coherence function. We also discuss in detail two analytic techniques that can be used for the treatment of the path integrals. M. I. Charnotskii 2015-10-07T14:56:47Z 2015-10-07T14:56:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1229 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1229 2015-10-07T14:56:47Z Bit error rate of focused Gaussian beams in weak oceanic turbulence: comment ecent calculations [J. Opt. Soc. Am. A 31, 1963 (2014) [CrossRef] ] of the scintillation index of focused beams did not take into account the second order of the perturbation theory, and therefore led the author to erroneous conclusions regarding dependence of the scintillation index for the focused beams on the aperture size. The log-normal intensity probability distribution used for the Bit Error Rate calculations in [J. Opt. Soc. Am. A 31, 1963 (2014) [CrossRef] ] is also invalid for the wide focused beams. As a result, most of the conclusions of [J. Opt. Soc. Am. A 31, 1963 (2014)] are incorrect. M. I. Charnotskii 2012-11-08T17:25:45Z 2013-05-07T18:44:08Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/564 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/564 2012-11-08T17:25:45Z Common omissions and misconceptions of wave propagation in turbulence: discussion This review paper addresses typical mistakes and omissions that involve theoretical research and modeling of optical propagation through atmospheric turbulence. We discuss the disregard of some general properties of narrow-angle propagation in refractive random media, the careless use of simplified models of turbulence, and omissions in the calculations of the second moment of the propagating wave. We also review some misconceptions regarding short-exposure imaging, propagation of polarized waves, and calculations of the scintillation index of the beam waves. M. I. Charnotskii 2013-04-12T22:50:58Z 2013-04-24T17:27:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/904 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/904 2013-04-12T22:50:58Z Energy conservation: a third constraint on the turbulent point spread function Energy conservation is an essential feature of optical waves propagating through refractive turbulence. It has been known for almost a quarter of a century that energy conservation has an important implication for the fluctuations in the images of the incoherent objects observed through turbulence, namely the image of the uniformly radiating area of an object does not scintillate. As a consequence, the low-contrast parts of an image exhibit weak fluctuation even for very strong turbulence, but scintillations near the sharp edges can be strong even for weak turbulence. The energy conservation property of the turbulent point spread function is essential for modeling turbulent image distortions, both for the development of the image processing techniques and for simulations of turbulent imaging. However, it is regularly overlooked in discussions of turbulent imaging theory and modeling in the current literature. We discuss the relations between energy conservation and anisoplanatism for the most common turbulence imaging models. Our analysis reveals that the only isoplanatic turbulent point spread function (PSF) that is compliant with energy conservation is the thin aperture plane phase screen. This implies that for near-the-ground imaging, and even for astronomical-type imaging under strong turbulence conditions, the turbulent PSF has to be modeled as a random function of four arguments with three functional constraints: non-negative values, finite bandwidth, and energy conservation. M. I. Charnotskii 2015-10-07T14:52:44Z 2015-10-07T14:52:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1228 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1228 2015-10-07T14:52:44Z Extended Huygens–Fresnel principle and optical waves propagation in turbulence: discussion Extended Huygens–Fresnel principle (EHF) currently is the most common technique used in theoretical studies of the optical propagation in turbulence. A recent review paper [J. Opt. Soc. Am. A 31, 2038 (2014) [CrossRef] ] cites several dozens of papers that are exclusively based on the EHF principle. We revisit the foundations of the EHF, and show that it is burdened by very restrictive assumptions that make it valid only under weak scintillation conditions. We compare the EHF to the less-restrictive Markov approximation and show that both theories deliver identical results for the second moment of the field, rendering the EHF essentially worthless. For the fourth moment of the field, the EHF principle is accurate under weak scintillation conditions, but is known to provide erroneous results for strong scintillation conditions. In addition, since the EHF does not obey the energy conservation principle, its results cannot be accurate for scintillations of partially coherent beam waves. M. I. Charnotskii 2012-12-21T20:46:41Z 2013-05-07T18:43:54Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/847 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/847 2012-12-21T20:46:41Z Intensity fluctuations of flat-topped beam in non-Kolmogorov weak turbulence: comment In J. Opt. Soc. Am. A 29, 169 (2012), Gerçekcioğlu and Baykal presented an investigation of the dependence of the scintillation index of flat-topped Gaussian beams on the exponent α of the power-law-type spectra of non-Kolmogorov turbulence. In particular, they found that the scintillation index reaches a maximum at α≈3.2. We show that this conclusion is an artifact of their specific calculation, and depends on the choice of the length unit. Gerçekcioğlu and Baykal's calculations are made for the 3<α<5 range of the spectral exponent. We show that for the homogeneous and isotropic turbulence the correct range is 3<α<4, when Markov approximation is used. M. I. Charnotskii 2015-04-20T20:19:46Z 2015-04-20T20:19:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1124 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1124 2015-04-20T20:19:46Z Optical phase under deep turbulence conditions The Markov approximation for waves in random media specifies that, under strong scintillation conditions, the optical field of unbounded waves has a normal probability distribution with zero mean. Using the coherence function provided by the Markov approximation, we calculate statistics of the phase of the optical field that accounts for the presence of multiple phase dislocations. We also develop and test a Monte Carlo model that generates the phase samples obeying these statistics. In contrast to numerous phase models described in the literature, this model generates discontinuous phase samples that contain optical vortices. M. I. Charnotskii 2016-04-11T21:19:25Z 2016-04-11T21:19:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1318 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1318 2016-04-11T21:19:25Z Optimal beam focusing through turbulence Beam spread and beam wandering are the most perceptible effects of atmospheric turbulence on propagating laser beams. The width of the mean irradiance profile is typically used to characterize the beam spread. This so-called long-term (LT) statistic allows for a relatively simple theoretical description. However, the LT beam size is not a very practical measure of the beam spread because its measurements are sensitive to the movements of the source and detector, and to the large-scale variations of the refractive index that are not associated with turbulence. The short-term (ST) beam spread is measured relative to the instantaneous position of the beam center and is free of these drawbacks, but has not been studied as thoroughly as the LT spread. We present a theoretical model for the ST beam irradiance that is based on the parabolic equation for the beam wave propagation in random media, and the Markov approximation for calculation of the statistics of the optical field, and discuss an approximation that allows introduction of the isoplanatic ST point spread function (PSF). Unlike the LT PSF, the ST PSF depends on the overall beam geometry. This allows optimization of the initial beam field in terms of minimizing the ST beam size at the observation plane. Calculations supporting this conjecture are presented for the simple case of the coherent Gaussian beam, and Kolmogorov turbulence. M. I. Charnotskii 2013-04-18T14:40:27Z 2013-04-24T17:36:49Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/933 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/933 2013-04-18T14:40:27Z Sparse spectrum model for a turbulent phase Monte Carlo (MC) simulation of phase front perturbations by atmospheric turbulence finds numerous applications for design and modeling of the adaptive optics systems, laser beam propagation simulations, and evaluating the performance of the various optical systems operating in the open air environment. Accurate generation of two-dimensional random fields of turbulent phase is complicated by the enormous diversity of scales that can reach five orders of magnitude in each coordinate. In addition there is a need for generation of the long "ribbons" of turbulent phase that are used to represent the time evolution of the wave front. This makes it unfeasible to use the standard discrete Fourier transform-based technique as a basis for the MC simulation algorithm. We propose a new model for turbulent phase: the sparse spectrum (SS) random field. The principal assumption of the SS model is that each realization of the random field has a discrete random spectral support. Statistics of the random amplitudes and wave vectors of the SS model are arranged to provide the required spectral and correlation properties of the random field. The SS-based MC model offers substantial reduction of computer costs for simulation of the wide-band random fields and processes, and is capable of generating long aperiodic phase "ribbons." We report the results of model trials that determine the number of sparse components, and the range of wavenumbers that is necessary to accurately reproduce the random field with a power-law spectrum. M. I. Charnotskii 2012-11-08T17:21:33Z 2013-04-24T17:39:20Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/563 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/563 2012-11-08T17:21:33Z Statistical modeling of the point spread function for imaging through turbulence We use a rigorous Markov approximation-based propagation model to calculate statistical properties of the instantaneous turbulent point spread function (PSF) for weak and strong turbulence conditions. Long-exposure PSF is well-known, and is currently widely used for estimates of optical system performance and simulation of the image distortions caused by turbulence. We discuss some peculiarities of the long-exposure PSF that are related to specifics of propagation in turbulence, which are often overlooked in the literature. Models for the short-exposure PSF have been used since the mid-1960s, and were the subject of some recent publications. We review a recently published model, and present sample calculations of the short-exposure PSF. Based on the available results of the optical propagation theory, we calculate variances of power fluctuations in the instantaneous PSF and the Strehl ratio, and covariance of the total power and the Strehl ratio. Analysis of the calculation results shows that for the most practical situations, the random Strehl ratio is a product of two uncorrelated, random variables—power and axial directivity. This information enables modeling of the instantaneous PSF with random width and height. M. I. Charnotskii 2014-01-08T20:52:39Z 2014-01-08T20:53:10Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/984 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/984 2014-01-08T20:52:39Z Statistics of the sparse spectrum turbulent phase A recently published sparse spectrum (SS) model of the phase front perturbations by atmospheric turbulence [J. Opt. Soc. Am. A 30, 479 (2013)] is based on the trigonometric series with discrete random support. The SS model enables fewer computational efforts, while preserving the wide range of scales typically associated with turbulence perturbations. We present an improved version of the SS model that accurately reproduces the power-law spectral density of the phase fluctuations in the arbitrary wide spectral band. We examine the higher-order statistics of the SS phase samples for four versions of the SS model. We also present the calculations of the long-exposure Strehl numbers and scintillation index for the different versions of the SS model. A nonoverlapping SS model with a log-uniform partition emerges as the most appropriate for the atmospheric turbulence representation. M. I. Charnotskii 2012-11-09T20:48:08Z 2013-05-08T18:01:52Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/591 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/591 2012-11-09T20:48:08Z Superresolution in dewarped anisoplanatic images I present a simple theoretical model for dewarped imaging through a turbulent medium and calculate the degree of superresolution that can be attained by dewarping the distorted instantaneous images registered through a turbulent atmosphere. The estimates show that on 1 km near the ground propagation path, spatial frequencies of the dewarped image can exceed the diffraction limit three times with a probability up to 10%. M. I. Charnotskii 2012-09-23T02:01:43Z 2013-05-13T15:19:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/112 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/112 2012-09-23T02:01:43Z An experimental test of the dual-frequency method for monitoring transverse currents The dual-frequency method for monitoring the transverse component of the velocity of current is tested using the data obtained earlier in a tidally forced flow through a channel. The turbulent properties of the flow cause fluctuations in the acoustic signals propagating through it. The fluctuations of such signals emitted at two different frequencies are coherent in the low-frequency band and noncoherent in the high-frequency region of the spectrum. The frequency separating these spectral regions is determined as the cutoff frequency of the coherence function and is directly related to the component of the current in the direction perpendicular to that of signal propagation. The results of measuring this component of the current are consistent with the data obtained with other independent methods and measurements. M. I. Charnotskii I. M. Fuks K. A. Naugolnykh A. V. Smirnov D. Di Iorio I. B. Esipov 2012-11-09T20:52:25Z 2013-05-08T18:07:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/593 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/593 2012-11-09T20:52:25Z Reply to comment by W. M. Connolley on "Was the 2003 European summer heat wave unusual in a global context?" N/A T. N. Chase K. Wolter R. A. Pielke, Sr. I. Rasool 2012-09-23T02:07:27Z 2013-05-10T20:23:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/113 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/113 2012-09-23T02:07:27Z Was the European summer heat wave unusual in a global context? We place the European summer heat wave of 2003 in the context of other extreme summer tropospheric temperature events from 22°N to 80°N since 1979, as well as globally using annual averages. The analysis is performed in terms of standard deviations (SD) exceeded and correlations between regional extremes and temperatures at larger spatial scales. As has been pointed out previously the heat wave was statistically unusual and was a deep tropospheric phenomenon. In this analysis we also find the following. (1) Extreme warm anomalies equally, or more, unusual than the 2003 heat wave occur regularly. (2) Extreme cold anomalies also occur regularly and occasionally exceed the magnitude of the 2003 warm anomaly in terms of the value of SD. (3) There is a correlation between global and hemispheric average temperature and the presence of warm or cold regional anomalies of the same sign (i.e., warmer than average years have more regional heat waves and colder than average years have more cold waves). (4) Natural variability in the form of El Niño and volcanic eruptions appear to be of much greater importance in causing extreme regional temperature anomalies than a simple upward trend in time. Extreme temperature anomalies in the wake of the 1997–98 El Niño were larger than the anomalies seen in summer 2003 both in area affected and SD extremes exceeded. (5) Regression analyses do not provide strong support for the idea that regional heat waves are increasing with time. T. N. Chase K. Wolter R. A. Pielke, Sr. I. Rasool 2015-04-24T19:43:34Z 2015-10-07T15:01:08Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1152 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1152 2015-04-24T19:43:34Z Modeling seasonal snowpack evolution in the complex terrain and forested Colorado Headwaters region: A model intercomparison study Correctly modeling snow is critical for climate models and for hydrologic applications. Snowpack simulated by six land surface models (LSM: Noah, Variable Infiltration Capacity, snow-atmosphere-soil transfer, Land Ecosystem-Atmosphere Feedback, Noah with Multiparameterization, and Community Land Model) were evaluated against 1 year snow water equivalent (SWE) data at 112 Snow Telemetry (SNOTEL) sites in the Colorado River Headwaters region and 4 year flux tower data at two AmeriFlux sites. All models captured the main characteristics of the seasonal SWE evolution fairly well at 112 SNOTEL sites. No single model performed the best to capture the combined features of the peak SWE, the timing of peak SWE, and the length of snow season. Evaluating only simulated SWE is deceiving and does not reveal critical deficiencies in models, because the models could produce similar SWE for starkly different reasons. Sensitivity experiments revealed that the models responded differently to variations of forest coverage. The treatment of snow albedo and its cascading effects on surface energy deficit, surface temperature, stability correction, and turbulent fluxes was a major intermodel discrepancy. Six LSMs substantially overestimated (underestimated) radiative flux (heat flux), a crucial deficiency in representing winter land-atmosphere feedback in coupled weather and climate models. Results showed significant intermodel differences in snowmelt efficiency and sublimation efficiency, and models with high rate of snow accumulation and melt were able to reproduce the observed seasonal evolution of SWE. This study highlights that the parameterization of cascading effects of snow albedo and below-canopy turbulence and radiation transfer is critical not only for SWE simulation but also for correctly capturing the winter land-atmosphere interactions. F. Chen M. Barlage M. Tewari R Rasmussen J. Jin D. Lettenmaier B. Livneh et al. 2012-11-13T17:37:01Z 2013-05-02T16:28:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/618 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/618 2012-11-13T17:37:01Z A numerical study of interactions between surface forcing and sea breeze circulations and their effects on stagnation in the greater Houston area High-resolution simulations from the Advanced Research Weather Research and Forecasting (ARW-WRF) model, coupled to an urban canopy model (UCM), are used to investigate impacts of soil moisture, sea surface temperature (SST), and city of Houston itself on the development of a stagnant wind event in the Houston-Galveston (HG) area on 30 August 2000. Surface and wind profiler observations are used to evaluate the performance of WRF-UCM. The model captures the observed nocturnal urban-heat-island intensity, diurnal rotation of surface winds, and the timing and vertical extent of sea breeze and its reversal in the boundary layer remarkably well. Using hourly SST slightly improves the WRF simulation of offshore wind and temperature. Model sensitivity tests demonstrate a delicate balance between the strength of sea breeze and prevailing offshore weak flow in determining the duration of the afternoon-evening stagnation in HG. When the morning offshore flow is weak (3–5 m s−1), variations (1°–3°C) in surface temperature caused by environmental conditions substantially modify the wind fields over HG. The existence of the city itself seems to favor stagnation. Extremely dry soils increase daytime surface temperature by about 2°C, produced more vigorous boundary layer and faster moving sea breeze, favoring stagnation during late afternoon. The simulation with dry soils produces a 3 h shorter duration stagnation in the afternoon and 4 h longer duration in the evening, which may lead to more severe nighttime air pollution. Hourly variations of SST in shallow water in the Galveston Bay substantially affect the low-level wind speed in HG. F. Chen S. Miao M. Tewari J.-W. Bao H. Kusaka 2013-08-26T21:57:37Z 2013-08-26T21:57:37Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/943 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/943 2013-08-26T21:57:37Z Cloud and Water Vapor Feedbacks to the El Niño Warming: Are They Still Biased in CMIP5 Models? Previous evaluations of model simulations of the cloud and water vapor feedbacks in response to El Niño warming have singled out two common biases in models from phase 3 of the Coupled Model Intercomparison Project (CMIP3): an underestimate of the negative feedback from the shortwave cloud radiative forcing (SWCRF) and an overestimate of the positive feedback from the greenhouse effect of water vapor. Here, the authors check whether these two biases are alleviated in the CMIP5 models. While encouraging improvements are found, particularly in the simulation of the negative SWCRF feedback, the biases in the simulation of these two feedbacks remain prevalent and significant. It is shown that bias in the SWCRF feedback correlates well with biases in the corresponding feedbacks from precipitation, large-scale circulation, and longwave radiative forcing of clouds (LWCRF). By dividing CMIP5 models into two categories—high score models (HSM) and low score models (LSM)—based on their individual skills of simulating the SWCRF feedback, the authors further find that ocean–atmosphere coupling generally lowers the score of the simulated feedbacks of water vapor and clouds but that the LSM is more affected by the coupling than the HSM. They also find that the SWCRF feedback is simulated better in the models that have a more realistic zonal extent of the equatorial cold tongue, suggesting that the continuing existence of an excessive cold tongue is a key factor behind the persistence of the feedback biases in models. L. Chen Y. Yu D.-Z. Sun 2016-04-11T21:22:51Z 2016-04-11T21:23:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1319 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1319 2016-04-11T21:22:51Z A Study of CINDY/DYNAMO MJO Suppressed Phase The diurnal variability and the environmental conditions that support the moisture resurgence of MJO events observed during the Cooperative Indian Ocean Experiment on Intraseasonal Variability (CINDY)/DYNAMO campaign in October–December 2011 are investigated using in situ observations and the cloud-resolving fully air–ocean–wave Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). Spectral density and wavelet analysis of the total precipitable water (TPW) constructed from the DYNAMO soundings and TRMM satellite precipitation reveal a deep layer of vapor resurgence during the observed Wheeler and Hendon real-time multivariate MJO index phases 5–8 (MJO suppressed phase), which include diurnal, quasi-2-, quasi-3–4-, quasi-6–8-, and quasi-16-day oscillations. A similar oscillatory pattern is found in the DYNAMO moorings sea surface temperature analysis, suggesting a tightly coupled atmosphere and ocean system during these periods. COAMPS hindcast focused on the 12–16 November 2011 event suggests that both the diurnal sea surface temperature (SST) pumping and horizontal and vertical moisture transport associated with the westward propagating mixed Rossby–Gravity (MRG) waves play an essential role in the moisture resurgence during this period. Idealized COAMPS simulations of MRG waves are used to estimate the MRG and diurnal SST contributions to the overall moisture increase. These idealized MRG sensitivity experiments showed the TPW increase varies from 9% to 13% with the largest changes occurring in the simulations that included a diurnal SST variation of 2.5°C as observed. S. Chen M. Flatau T. G. Jensen T. Shinoda J. Schmidt P. May J. Cummings M. Liu P. E. Ciesielski C. W. Fairall et al. 2015-04-24T19:52:45Z 2015-10-07T15:04:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1153 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1153 2015-04-24T19:52:45Z Comparison of the sensitivity of surface downward longwave radiation to changes in water vapor at two high elevation sites Among the potential reasons for enhanced warming rates in many high elevation regions is the nonlinear relationship between surface downward longwave radiation (DLR) and specific humidity (q). In this study we use ground-based observations at two neighboring high elevation sites in Southwestern Colorado that have different local topography and are 1.3 km apart horizontally and 348 m vertically. We examine the spatial consistency of the sensitivities (partial derivatives) of DLR with respect to changes in q, and the sensitivities are obtained from the Jacobian matrix of a neural network analysis. Although the relationship between DLR and q is the same at both sites, the sensitivities are higher when q is smaller, which occurs more frequently at the higher elevation site. There is a distinct hourly distribution in the sensitivities at both sites especially for high sensitivity cases, although the range is greater at the lower elevation site. The hourly distribution of the sensitivities relates to that of q. Under clear skies during daytime, q is similar between the two sites, however under cloudy skies or at night, it is not. This means that the DLR–q sensitivities are similar at the two sites during daytime but not at night, and care must be exercised when using data from one site to infer the impact of water vapor feedbacks at another site, particularly at night. Our analysis suggests that care should be exercised when using the lapse rate adjustment to infill high frequency data in a complex topographical region, particularly when one of the stations is subject to cold air pooling as found here. Y. Chen C. M. Naud I. Rangwala C. C. Landry J. R. Miller 2015-11-19T23:15:36Z 2016-07-13T22:19:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1292 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1292 2015-11-19T23:15:36Z How Has Human-induced Climate Change Affected California Drought Risk? The current California drought has cast a heavy burden on statewide agriculture and water resources, further exacerbated by concurrent extreme high temperatures. Furthermore, industrial-era global radiative forcing brings into question the role of long-term climate change on CA drought. How has human-induced climate change affected California drought risk? Here, observations and model experimentation are applied to characterize this drought employing metrics that synthesize drought duration, cumulative precipitation deficit, and soil moisture depletion. The model simulations show that increases in radiative forcing since the late 19th Century induces both increased annual precipitation and increased surface temperature over California, consistent with prior model studies and with observed long-term change. As a result, there is no material difference in the frequency of droughts defined using bivariate indicators of precipitation and near-surface (10-cm) soil moisture, because shallow soil moisture responds most sensitively to increased evaporation driven by warming, which compensates the increase in the precipitation. However, when using soil moisture within a deep root zone layer (1-m) as co-variate, droughts become less frequent because deep soil moisture responds most sensitively to increased precipitation. The results illustrate the different land surface responses to anthropogenic forcing that are relevant for near-surface moisture exchange and for root zone moisture availability. The latter is especially relevant for agricultural impacts as the deep layer dictates moisture availability for plants, trees, and many crops. The results thus indicate the net effect of climate change has made agricultural drought less likely, and that the current severe impacts of drought on California's agriculture has not been substantially caused by long-term climate changes. L. Cheng M. P. Hoerling A. AghaKouchak B. Livneh X.-W. Quan J. K. Eischeid 2017-01-17T23:30:26Z 2017-02-08T20:32:54Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1465 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1465 2017-01-17T23:30:26Z Planning for climate change impacts on hydropower in the Far North Unlike much of the contiguous United States, new hydropower development continues in the Far North, where climate models project precipitation will likely increase over the next century. Regional complexities in the Arctic and sub-Arctic, such as glacier recession and permafrost thaw, however, introduce uncertainties about the hydrologic responses to climate change that impact water resource management. This work reviews hydroclimate changes in the Far North and their impacts on hydropower; it provides a template for application of current techniques for prediction and estimating uncertainty, and it describes best practices for integrating science into management and decision-making. The growing number of studies on hydrologic impacts suggests that information resulting from climate change science has matured enough that it can and should be integrated into hydropower scoping, design, and management. Continuing to ignore the best available information in lieu of status quo planning is likely to prove costly to society in the long term. J. E. Cherry C. Knapp S. Trainor A. J. Ray M. Tedesche S. Walker 2014-07-15T19:55:47Z 2014-07-15T19:55:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1062 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1062 2014-07-15T19:55:47Z Effects of Near-Surface Soil Moisture on GPS SNR Data: Development of a Retrieval Algorithm for Soil Moisture Global Positioning System (GPS) multipath signals can be used to infer volumetric soil moisture around a GPS antenna. While most GPS users concentrate on the signal that travels directly from the satellite to the antenna, the signal that is reflected by nearby surfaces contains information about the environment surrounding the antenna. The interference between the direct and reflected signals produces a modulation that can be observed in temporal variations of the signal-to-noise ratio (SNR) data recorded by the GPS receiver. Changes in the dielectric constant of the soil, which are associated with fluctuations in soil moisture, affect the effective reflector height, amplitude, and phase of the multipath modulation. Empirical studies have shown that these changes in SNR data are correlated with near-surface volumetric soil moisture. This study uses an electrodynamic single-scattering forward model to test the empirical relationships observed in field data. All three GPS interferogram metrics (effective reflector height, phase, and amplitude) are affected by soil moisture in the top 5 cm of the soil; surface soil moisture (<;1-cm depth) exerts the strongest control. Soil type exerts a negligible impact on the relationships between GPS interferogram metrics and soil moisture. Phase is linearly correlated with surface soil moisture. The slope of the relationship is similar to that observed in field data. Amplitude and effective reflector height are also affected by soil moisture, although the relationship is nonlinear. Phase is the best metric derived from GPS data to use as a proxy for soil moisture variations. C. C. Chew E. E. Small K. M. Larson V. U. Zavorotny 2015-04-24T20:22:48Z 2015-10-07T15:06:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1155 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1155 2015-04-24T20:22:48Z Vegetation Sensing Using GPS-Interferometric Reflectometry: Theoretical Effects of Canopy Parameters on Signal-to-Noise Ratio Data The potential to use GPS signal-to-noise ratio (SNR) data to estimate changes in vegetation surrounding a ground-based antenna is evaluated. A 1-D plane-stratified model that simulates the response of GPS SNR data to changes in both soil moisture and vegetation is presented. The model is validated against observations of SNR data from four field sites with varying vegetation cover. Validation shows that the average correlation between modeled and observed SNR data is higher than the average correlation between concurrent SNR observations from different satellite tracks at a site. The model also reproduces variations in the SNR metrics amplitude, phase, and effective reflector height over a range of vegetation wet weights from 0 to 4 kg · m-2, with r2 values of 0.79, 0.84, and 0.62, respectively. Model simulations indicate that the amplitude of SNR oscillations may be used to estimate vegetation amount when vegetation wet weight is below 1.5 kg · m-2. When vegetation wet weight exceeds 1.5 kg · m-2, the sensitivity of amplitude to changes in vegetation amount decreases. Phase of SNR oscillations also varies consistently with vegetation up to 1.5 kg · m-2. However, phase is also very sensitive to soil moisture variations, thus limiting its utility for estimating vegetation. Effective reflector height is not a consistent indicator of vegetation change. Beyond 1.5 kg · m-2, the constant frequency assumption used to characterize SNR fluctuations does not adequately describe observed data. A more complex approach than the standard SNR metrics used here is required to extend GPS-Interferometric Reflectometry sensing to thicker canopies. C. C. Chew E. E. Small K. M. Larson V. U. Zavorotny 2017-04-11T16:05:56Z 2017-04-11T16:05:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1468 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1468 2017-04-11T16:05:56Z Evaluation of single and multiple Doppler lidar techniques to measure complex flow during the XPIA field campaign Accurate three-dimensional information of wind flow fields can be an important tool in not only visualizing complex flow but also understanding the underlying physical processes and improving flow modeling. However, a thorough analysis of the measurement uncertainties is required to properly interpret results. The XPIA (eXperimental Planetary boundary layer Instrumentation Assessment) field campaign conducted at the Boulder Atmospheric Observatory (BAO) in Erie, CO, from 2 March to 31 May 2015 brought together a large suite of in situ and remote sensing measurement platforms to evaluate complex flow measurement strategies. In this paper, measurement uncertainties for different single and multi-Doppler strategies using simple scan geometries (conical, vertical plane and staring) are investigated. The tradeoffs (such as time–space resolution vs. spatial coverage) among the different measurement techniques are evaluated using co-located measurements made near the BAO tower. Sensitivity of the single-/multi-Doppler measurement uncertainties to averaging period are investigated using the sonic anemometers installed on the BAO tower as the standard reference. Finally, the radiometer measurements are used to partition the measurement periods as a function of atmospheric stability to determine their effect on measurement uncertainty. It was found that with an increase in spatial coverage and measurement complexity, the uncertainty in the wind measurement also increased. For multi-Doppler techniques, the increase in uncertainty for temporally uncoordinated measurements is possibly due to requiring additional assumptions of stationarity along with horizontal homogeneity and less representative line-of-sight velocity statistics. It was also found that wind speed measurement uncertainty was lower during stable conditions compared to unstable conditions. A. Choukulkar W. A. Brewer S. P. Sandberg A. Weickmann T. A. Bonin R. M. Hardesty J. K. Lundquist R. Delgado G. V. Iungo R. Ashton M. Debnath L. Bianco J. M. Wilczak S. Oncley D. E. Wolfe 2012-11-09T20:57:13Z 2013-02-05T22:21:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/596 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/596 2012-11-09T20:57:13Z Effects of underwater sound and surface ripples on scattered laser light The acousto-optic interaction at a water surface perturbed by random waves and by an underwater sound source is studied. The interferometric method is applied to measure the features of the power spectra of the scattered light field. Detection of sound-induced perturbation of the rough surface is performed. The corresponding theory of the scattered light spectra modulation is presented and its results are compared with the data of the experiment. J. H. Churnside H. E. Bravo K. A. Naugolnykh I. M. Fuks 2015-10-07T15:11:28Z 2015-10-07T15:11:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1230 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1230 2015-10-07T15:11:28Z Optical remote sensing of sound in the ocean We propose a remote sensing technique to measure sound in the upper ocean. The objective is a system that can be flown on an aircraft. Conventional acoustic sensors are ineffective in this application, because almost none (∼0.1%) of the sound in the ocean is transmitted through the water/air interface. The technique is based on the acoustic modulation of naturally occurring bubbles near the sea surface. It is clear from the ideal gas law that the volume of a bubble will decrease if the pressure is increased, as long as the number of gas molecules and temperature remain constant. The pressure variations associated with the acoustic field will therefore induce proportional volume fluctuations of the insonified bubbles. The lidar return from a collection of bubbles is proportional to the total void fraction, independent of the bubble size distribution. This implies that the lidar return from a collection of insonified bubbles will be modulated at the acoustic frequencies, independent of the bubble size distribution. Moreover, that modulation is linearly related to the sound pressure. A laboratory experiment confirmed the basic principles, and estimates of signal-to-noise ratio suggest that the technique will work in the open ocean. J. H. Churnside K. A. Naugolnykh R. Marchbanks 2012-10-01T16:57:28Z 2013-05-03T14:50:41Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/282 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/282 2012-10-01T16:57:28Z Thermal Footprints of Whales Under the right meteorological conditions, whales can leave a trail of cool spots on the ocean surface that are detectable in infrared images. When the wind is light and the sun is shining, the surface water warms to produce a thermal gradient in the top few meters of the ocean. Under these conditions, whales swimming near the surface produce a jet of cooler water with each upward motion of the tail fluke. When this jet reaches the surface, it will produce a temperature difference that can persist for several minutes. In this paper, we report the first observations of these thermal footprints; we discovered them in infrared images made by a camera mounted in a light twin-engine airplane. We also describe their formation and dissipation. J. H. Churnside L. Ostrovsky T. Veenstra 2012-11-13T17:39:09Z 2013-05-02T16:28:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/619 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/619 2012-11-13T17:39:09Z On the Persistence of Cold-Season SST Anomalies Associated with the Annular Modes In this study, a simple stochastic climate model is used to examine the impact of the ocean mixed layer depth, surface turbulent energy fluxes, and Ekman currents on the persistence of cold-season extratropical sea surface temperature (SST) anomalies associated with variability in the annular modes of atmospheric circulation in both hemispheres. Observational analysis reveals that during the cold season, SST anomalies associated with the southern annular mode (SSTSAM) persist considerably longer than those associated with the northern annular mode (SSTNAM). Using the simple model, it is shown that the persistence of the cold-season SSTSAM is consistent with the simple stochastic climate paradigm in which the atmospheric forcing is approximated as white noise, and the persistence of SST anomalies can be largely determined by the thermal inertia of the ocean mixed layer. In the North Atlantic, however, the simple climate model overestimates the persistence of the cold-season SSTNAM. It is thought that this overestimate occurs because the NAM-related heat flux forcing cannot be described purely as white noise but must also include a feedback from the underlying SST anomalies. L. M. Ciasto M. A. Alexander C. Deser M. H. England 2012-09-26T15:50:59Z 2014-07-01T14:54:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/217 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/217 2012-09-26T15:50:59Z Dual polarization radar rainfall estimation, in "Rainfall, State of the Science" Dual-polarization radar is a critical tool for weather research applications, including rainfall estimation, and is at the verge of being a key instrument for operational meteorologists. This new radar system is being integrated into radar networks around the world, including the planned upgrade of the U.S. National Weather Service Weather Surveillance Radar, 1988 Doppler radars. Dual polarization offers several advantages compared to single-polarization radar systems, including additional information about the size, shape, and orientation of hydrometeors. This information can be used to more accurately retrieve characteristics of the drop size distribution, identify types of hydrometeors, correct for signal loss (attenuation) in heavy precipitation, and more easily identify spurious echo scatterers. In addition to traditional backscatter measurements, differential propagation phase characteristics allow for rainfall estimation that is immune to absolute calibration of the radar system, attenuation effects, as well as partial beam blocking. By combining different radar measurements, rainfall retrieval algorithms have developed that minimize the error characteristics of the different rainfall estimators, while at the same time taking advantage of the data quality enhancements. Although dual-polarization techniques have been applied to S band and C band radar systems for several decades, polarization diversity at higher frequencies including X band are now widely available to the radar community. This chapter provides an overview of dual-polarization rainfall estimation applications that are typically utilized at X, C, and S bands. The concept of distinguishing basic and applied science issues and their impact on rainfall estimation is introduced. Various dual-polarization radar rainfall techniques are discussed, emphasizing the strengths and weaknesses of various estimators at different frequencies. R. Cifelli V. Chandrasekar 2012-11-13T17:41:49Z 2014-07-01T14:55:31Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/620 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/620 2012-11-13T17:41:49Z A New Dual-Polarization Radar Rainfall Algorithm: Application in Colorado Precipitation Events The efficacy of dual-polarization radar for quantitative precipitation estimation (QPE) has been demonstrated in a number of previous studies. Specifically, rainfall retrievals using combinations of reflectivity (Zh), differential reflectivity (Zdr), and specific differential phase (Kdp) have advantages over traditional Z–R methods because more information about the drop size distribution (DSD) and hydrometeor type are available. In addition, dual-polarization-based rain-rate estimators can better account for the presence of ice in the sampling volume. An important issue in dual-polarization rainfall estimation is determining which method to employ for a given set of polarimetric observables. For example, under what circumstances does differential phase information provide superior rain estimates relative to methods using reflectivity and differential reflectivity? At Colorado State University (CSU), an optimization algorithm has been developed and used for a number of years to estimate rainfall based on thresholds of Zh, Zdr, and Kdp. Although the algorithm has demonstrated robust performance in both tropical and midlatitude environments, results have shown that the retrieval is sensitive to the selection of the fixed thresholds. In this study, a new rainfall algorithm is developed using hydrometeor identification (HID) to guide the choice of the particular rainfall estimation algorithm. A separate HID algorithm has been developed primarily to guide the rainfall application with the hydrometeor classes, namely, all rain, mixed precipitation, and all ice. Both the data collected from the S-band Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL) radar and a network of rain gauges are used to evaluate the performance of the new algorithm in mixed rain and hail in Colorado. The evaluation is also performed using an algorithm similar to the one developed for the Joint Polarization Experiment (JPOLE). Results show that the new CSU HID-based algorithm provides good performance for the Colorado case studies presented here. R. Cifelli V. Chandrasekar S. Lim P. C. Kennedy Y. Wang S. A. Rutledge 2012-09-26T15:55:20Z 2013-05-08T14:54:21Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/218 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/218 2012-09-26T15:55:20Z Characteristics of an African easterly wave observed during NAMMA The evolution of an African easterly wave is described using ground-based radar and ancillary datasets from three locations in West Africa: Niamey, Niger (continental), Dakar, Senegal (coastal), and Praia, Republic of Cape Verde (oceanic). The data were collected during the combined African Monsoon Multidisciplinary Analyses (AMMA) and NASA AMMA (NAMMA) campaigns in August–September 2006. Two precipitation events originated within the wave circulation and propagated with the wave across West Africa. Mesoscale convective systems (MCSs) associated with these events were identified at all three sites ahead of, within, and behind the 700-mb wave trough. An additional propagating event was indentified that originated east of the wave and moved through the wave circulation. The MCS activity associated with this event did not show any appreciable change resulting from its interaction with the wave. The MCS characteristics at each site were different, likely due to a combination of life cycle effects and changes in relative phasing between the propagating systems and the position of low-level convergence and thermodynamic instability associated with the wave. At the ocean and coastal sites, the most intense convection occurred ahead of the wave trough where both high CAPE and low-level convergence were concentrated. At the continental site, convection was relatively weak owing to the fact that the wave dynamics and thermodynamics were not in sync when the systems passed through Niamey. The only apparent effect of the wave on MCS activity at the continental site was to extend the period of precipitation activity during one of the events that passed through coincident with the 700-mb wave trough. Convective organization at the land sites was primarily in the form of squall lines and linear MCSs oriented perpendicular to the low-level shear. The organization at the oceanic site was more complicated, transitioning from linear MCSs to widespread stratiform cloud with embedded convection. The precipitation activity was also much longer lived at the oceanic site due to the wave becoming nearly stationary near the Cape Verdes, providing an environment supportive of deep convection for an extended period. R. Cifelli T. Lang S. Rutledge N. Guy E. Zipser J. Zawislak R. Holzworth 2014-07-15T19:26:19Z 2014-07-15T19:26:19Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1059 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1059 2014-07-15T19:26:19Z A Multisensor Comparison of Ocean Wave Frequency Spectra from a Research Vessel during the Southern Ocean Gas Exchange Experiment Obtaining accurate measurements of wave statistics from research vessels remains a challenge due to the platform motion. One principal correction is the removal of ship heave and Doppler effects from point measurements. Here, open-ocean wave measurements were collected using a laser altimeter, a Doppler radar microwave sensor, a radar-based system, and inertial measurement units. Multiple instruments were deployed to capture the low- and high-frequency sea surface displacements. Doppler and motion correction algorithms were applied to obtain a full 1D (0.035–1.3 ± 0.2 Hz) wave spectrum. The radar-based system combined with the laser altimeter provided the optimal low- and high-frequency combination, producing a frequency spectrum in the range from 0.035 to 1.2 Hz for cruising speeds ≤3 m s−1 with a spectral rolloff of f−4 Hz and noise floor of −20/−30 dB. While on station, the significant wave height estimates were comparable within 10%–15% among instrumentation. Discrepancies in the total energy and in the spectral shape between instruments arise when the ship is in motion. These differences can be quantified using the spectral behavior of the measurements, accounting for aliasing and Doppler corrections. The inertial sensors provided information on the amplitude of the ship's modulation transfer function, which was estimated to be ~1.3 ± 0.2 while on station and increased while underway [2.1 at ship-over-ground (SOG) speed; 4.3 m s−1]. The correction scheme presented here is adequate for measurements collected at cruising speeds of 3 m s−1 or less. At speeds greater than 5 m s−1, the motion and Doppler corrections are not sufficient to correct the observed spectral degradation. A. Cifuentes-Lorenzen J. B. Edson C. J. Zappa L. Bariteau 2012-10-01T16:57:35Z 2013-08-27T21:43:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/283 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/283 2012-10-01T16:57:35Z Comparison of Ground-Based Millimeter-Wave Observations and Simulations in the Arctic Winter. During the Radiative Heating in Underexplored Bands Campaign (RHUBC), held in February-March 2007, three millimeter-wave radiometers were operated at the Atmospheric Radiation Measurement Program's site in Barrow, Alaska. These radiometers contain several channels located around the strong 183.31-GHz water vapor line, which is crucial for ground-based water-vapor measurements in very dry conditions, typical of the Arctic. Simultaneous radiosonde observations were carried out during conditions with very low integrated-water-vapor (IWV) content (< 2 mm). Observations from the three instruments are compared, accounting for their different design characteristics. The overall agreement during RHUBC among the three instruments and between instruments and forward model is discussed quantitatively. In general, the instrument cross-validation performed for sets of channel pairs showed agreement within the total expected uncertainty. The consistency between instruments allows the determination of the IWV to within around 2% for these dry conditions. Comparisons between these data sets and forward-model simulations using radiosondes as input show spectral features in the brightness-temperature residuals, indicating some degree of inconsistency between the instruments and the forward model. The most likely cause of forward-model error is systematic errors in the radiosonde humidity profiles. D. Cimini F. Nasir E. R. Westwater V. H. Payne D. D. Turner E. J. Milawer M. L. Exner M. P. Cadeddu 2012-09-26T16:00:23Z 2013-08-27T21:43:17Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/219 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/219 2012-09-26T16:00:23Z Temperature and humidity profiling in the Arctic using ground-based millimeter-wave radiometry and 1DVAR A 1-D variational (1DVAR) retrieval technique has been developed for obtaining temperature and humidity profiles from observations of the Ground-Based Scanning Radiometer (GSR) operating at millimeter-wavelengths. The GSR was deployed in two Arctic experiments held at the Atmospheric Radiation Measurement Program in Barrow, Alaska. Temperature and humidity profiles retrieved with the 1DVAR technique are compared with simultaneous radiosonde observations (RAOBs) during the Radiative Heating in Underexplored Bands Campaign (February-March 2007). Examples and statistical results are presented and discussed to demonstrate the achieved retrieval accuracy and vertical resolution. The 1DVAR retrievals based on GSR observations improve the NWP background up to 5 km, particularly in the lower 3 km. The present implementation achieved an root-mean-square (rms) error with respect to RAOB within 1.5 K for temperature and 0.10 g/kg for humidity profiles of up to 5 km in height, with 2.9 and 2.0 degrees of freedom for signal, respectively. Using the interlevel covariance definition of the vertical resolution, the 1DVAR retrievals showed a < 1-km vertical resolution of up to 5 km for both temperature and humidity profiles. The integrated water vapor obtained from the retrieved humidity profiles showed an rms accuracy within 0.10 kg/m2 , with small bias (< 0.01 kg/m2) and excellent correlation (0.96). D. Cimini E. R. Westwater A. J. Gasiewski 2016-10-14T17:38:25Z 2016-10-14T17:38:25Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1429 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1429 2016-10-14T17:38:25Z Coyote unmanned aircraft system observations in Hurricane Edouard (2014) Horizontal wind, temperature, and moisture observations are presented from two Coyote unmanned aircraft system (UAS) flights in the boundary layer of Hurricane Edouard (2014). The first flight sampled the meteorological conditions in the eye and eyewall at altitudes from 900 to 1500 m while Edouard was a major hurricane (105 kt) on 16 September 2014. The following day, a second Coyote sampled the inflow layer outside of the storm core at ~760 m altitude, when Edouard had weakened to an 80-kt hurricane. These flights represent the first deployments of a UAS from an airborne manned aircraft into a tropical cyclone. Comparisons between the Coyote data and the Lockheed WP-3D Orion (WP-3D) flight-level measurements and analyses constructed from dropsonde data are also provided. On 16 September 2014, the Coyote-measured horizontal wind speeds agree, on average, to within ~1 m s−1 of the wind speeds observed by the WP-3D and reproduce the shape of the radial wind profile from the WP-3D measurements. For the inflow layer experiment on 17 September, the mean wind speeds from the Coyote and the dropsonde analysis differ by only 0.5 m s−1, while the Coyote captured increased variability (σ = 3.4 m s−1) in the horizontal wind field compared to the dropsonde analysis (σ = 2.2 m s−1). Thermodynamic data from the Coyote and dropsondes agree well for both flights, with average discrepancies of 0.4°C and 0.0°C for temperature and 0.7°C and 1.3°C for dew point temperature on 16 and 17 September, respectively J. J. Cione E. A. Kalina E. W. Uhlhorn A. M. Farber B. Damiano 2012-10-01T18:49:38Z 2013-04-25T19:10:06Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/291 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/291 2012-10-01T18:49:38Z NASA Cold Land Processes Experiment (CLPX 2002/03): Airborne Remote Sensing. This paper describes the airborne data collected during the 2002 and 2003 Cold Land Processes Experiment (CLPX). These data include gamma radiation observations, multi- and hyperspectral optical imaging, optical altimetry, and passive and active microwave observations of the test areas. The gamma observations were collected with the NOAA/National Weather Service Gamma Radiation Detection System (GAMMA). The CLPX multispectral optical data consist of very high-resolution color-infrared orthoimagery of the intensive study areas (ISAs) by TerrainVision. The airborne hyperspectral optical data consist of observations from the NASA Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). Optical altimetry measurements were collected using airborne light detection and ranging (lidar) by TerrainVision. The active microwave data include radar observations from the NASA Airborne Synthetic Aperture Radar (AIRSAR), the Jet Propulsion Laboratory's Polarimetric Ku-band Scatterometer (POLSCAT), and airborne GPS bistatic radar data collected with the NASA GPS radar delay mapping receiver (DMR). The passive microwave data consist of observations collected with the NOAA Polarimetric Scanning Radiometer (PSR). All of the airborne datasets described here and more information describing data collection and processing are available online. D. Cline S. Yueh B. Chapman B. B. Stankov A. J. Gasiewski D. Masters K. Elder R. Kelly T. H. Painter S. Miller S. Katzberg L. Mahrt 2015-04-24T20:26:56Z 2015-10-07T15:13:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1156 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1156 2015-04-24T20:26:56Z Measurements of diurnal variations and eddy covariance (EC) fluxes of glyoxal in the tropical marine boundary layer: description of the Fast LED-CE-DOAS instrument Here we present first eddy covariance (EC) measurements of fluxes of glyoxal, the smallest α-dicarbonyl product of hydrocarbon oxidation, and a precursor for secondary organic aerosol (SOA). The unique physical and chemical properties of glyoxal – i.e., high solubility in water (effective Henry's law constant, KH = 4.2 × 105 M atm−1) and short atmospheric lifetime (~2 h at solar noon) – make it a unique indicator species for organic carbon oxidation in the marine atmosphere. Previous reports of elevated glyoxal over oceans remain unexplained by atmospheric models. Here we describe a Fast Light-Emitting Diode Cavity-Enhanced Differential Optical Absorption Spectroscopy (Fast LED-CE-DOAS) instrument to measure diurnal variations and EC fluxes of glyoxal and inform about its unknown sources. The fast in situ sensor is described, and first results are presented from a cruise deployment over the eastern tropical Pacific Ocean (20° N to 10° S; 133 to 85° W) as part of the Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOCs (TORERO) field experiment (January to March 2012). The Fast LED-CE-DOAS is a multispectral sensor that selectively and simultaneously measures glyoxal (CHOCHO), nitrogen dioxide (NO2), oxygen dimers (O4), and water vapor (H2O) with ~2 Hz time resolution (Nyquist frequency ~1 Hz) and a precision of ~40 pptv Hz−0.5 for glyoxal. The instrument is demonstrated to be a "white-noise" sensor suitable for EC flux measurements. Fluxes of glyoxal are calculated, along with fluxes of NO2, H2O, and O4, which are used to aid the interpretation of the glyoxal fluxes. Further, highly sensitive and inherently calibrated glyoxal measurements are obtained from temporal averaging of data (e.g., detection limit smaller than 2.5 pptv in an hour). The campaign average mixing ratio in the Southern Hemisphere (SH) is found to be 43 ± 9 pptv glyoxal, which is higher than the Northern Hemisphere (NH) average of 32 ± 6 pptv (error reflects variability over multiple days). The diurnal variation of glyoxal in the marine boundary layer (MBL) is measured for the first time, and mixing ratios vary by ~8 pptv (NH) and ~12 pptv (SH) over the course of 24 h. Consistently, maxima are observed at sunrise (NH: 35 ± 5 pptv; SH: 47 ± 7 pptv), and minima at dusk (NH: 27 ± 5 pptv; SH: 35 ± 8 pptv). In both hemispheres, the daytime flux was directed from the atmosphere into the ocean, indicating that the ocean is a net sink for glyoxal during the day. After sunset the ocean was a source for glyoxal to the atmosphere (positive flux) in the SH; this primary ocean source was operative throughout the night. In the NH, the nighttime flux was positive only shortly after sunset and negative during most of the night. Positive EC fluxes of soluble glyoxal over oceans indicate the presence of an ocean surface organic microlayer (SML) and locate a glyoxal source within the SML. The origin of most atmospheric glyoxal, and possibly other oxygenated hydrocarbons over tropical oceans, remains unexplained and warrants further investigation. S. Coburn I. Ortega R. Thalman B. W. Blomquist C. W. Fairall R. Volkamer 2012-10-15T23:23:43Z 2013-05-07T17:27:13Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/297 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/297 2012-10-15T23:23:43Z Boundary-layer dynamics and its influence on atmospheric chemistry at Summit, Greenland Sonic anemometer turbulence measurements were made at Summit, Greenland during summer 2004 and spring 2005. These measurements allow for the characterization of the variability of the atmospheric boundary layer at this site by describing seasonal and diurnal changes in sensible heat flux and boundary layer stability as well as providing estimates of mixing layer height. Diurnal sensible heat fluxes at Summit ranged from −18 to −2 W m−2 in the spring and from −7 to +10 W m−2 in the summer. Sustained stable surface layer conditions and low wind speeds occured during the spring but not during the summer months. Unstable conditions were not observed at Summit until late April. Diurnal cycles of convective conditions during the daytime (0700–1700 h local time) were observed throughout July and August. Boundary layer heights, which were estimated for neutral to stable conditions, averaged 156 m for the spring 2005 observations. Comparisons of the boundary layer characteristics of Summit with those from South Pole, Antarctica, provide possible explanations for the significant differences in snowpack and surface-layer chemistry between the two sites. L. Cohen D. Helmig W. D. Neff A. A. Grachev C. W. Fairall 2012-11-13T17:44:37Z 2013-05-02T16:29:33Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/621 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/621 2012-11-13T17:44:37Z Past and ongoing shifts in Joshua tree distribution support future modeled range contraction The future distribution of the Joshua tree (Yucca brevifolia) is projected by combining a geostatistical analysis of 20th-century climates over its current range, future modeled climates, and paleoecological data showing its response to a past similar climate change. As climate rapidly warmed 11 700 years ago, the range of Joshua tree contracted, leaving only the populations near what had been its northernmost limit. Its ability to spread northward into new suitable habitats after this time may have been inhibited by the somewhat earlier extinction of megafaunal dispersers, especially the Shasta ground sloth. We applied a model of climate suitability for Joshua tree, developed from its 20th-century range and climates, to future climates modeled through a set of six individual general circulation models (GCM) and one suite of 22 models for the late 21st century. All distribution data, observed climate data, and future GCM results were scaled to spatial grids of 1 km and 4 km in order to facilitate application within this topographically complex region. All of the models project the future elimination of Joshua tree throughout most of the southern portions of its current range. Although estimates of future monthly precipitation differ between the models, these changes are outweighed by large increases in temperature common to all the models. Only a few populations within the current range are predicted to be sustainable. Several models project significant potential future expansion into new areas beyond the current range, but the species' historical and current rates of dispersal would seem to prevent natural expansion into these new areas. Several areas are predicted to be potential sites for relocation/assisted migration. This project demonstrates how information from paleoecology and modern ecology can be integrated in order to understand ongoing processes and future distributions. Read More: http://www.esajournals.org/doi/abs/10.1890/09-1800.1 K. L. Cole K. Ironside J. K. Eischeid G. M. Garfin P. B. Duffy C. Toney 2012-11-06T18:40:55Z 2013-02-05T00:40:40Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/490 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/490 2012-11-06T18:40:55Z High-resolution simulations and microphysical validation of an orographic precipitation event over the Wasatch Mountains during IPEX IOP3 This paper investigates the kinematic flow and precipitation evolution of a winter storm over and upstream of the Wasatch Mountains [Intermountain Precipitation Experiment third intensive observing period (IPEX IOP3)] using a multiply nested version of the fifth-generation Pennsylvania State University (PSU)––National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5). Validation using in situ aircraft data, radiosondes, ground-based radar, and surface observations showed that the MM5, which featured four domains with 36-, 12-, 4-, and 1.33-km grid spacing, realistically simulated the observed partial blocking of the 8–12 m s−1 ambient southwesterly flow and development of a convergence zone and enhanced lowland precipitation region upwind of the initial Wasatch slope. The MM5 also properly simulated the advance of this convergence zone toward the base of the Wasatch during the passage of a midlevel trough, despite not fully capturing the westerly wind shift accompanying the trough. Accurate simulation of the observed precipitation over the central Wasatch Mountains (within 25% of observed at all stations) required a horizontal grid spacing of 1.33 km. Despite close agreement with the observed surface precipitation, the Reisner2 bulk microphysical scheme produced too much supercooled cloud water and too little snow aloft. A model microphysical budget revealed that the Reisner2 generated over half of the surface precipitation through riming and accretion, rather than snow deposition and aggregation as implied by the observations. Using an intercept for the snow size distribution that allows for greater snow concentrations aloft improved the snow predictions and reduced the cloud water overprediction. Sensitivity studies illustrate that the reduced surface drag of the Great Salt Lake (GSL) enhanced the convergence zone and associated lowland precipitation enhancement upstream of the Wasatch Mountains. The presence of mountain ranges south of the Great Salt Lake appears to have weakened the along-barrier flow and windward convergence, resulting in a slight decrease in windward precipitation enhancement. Diabatic cooling from falling precipitation was also important for maintaining the blocked flow. B. A. Colle J. B. Wolfe W. J. Steenburgh D. E. Kingsmill et al. 2017-05-05T19:44:58Z 2017-05-05T19:44:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1490 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1490 2017-05-05T19:44:58Z Doppler Correction of Wave Frequency Spectra Measured by Underway Vessels "Sea State and Boundary Layer Physics of the Emerging Arctic Ocean" is an ongoing Departmental Research Initiative sponsored by the Office of Naval Research (http://www.apl.washington.edu/project/project.php?id=arctic_sea_state). The field component took place in the fall of 2015 within the Beaufort and Chukchi Seas and involved the deployment of a number of wave instruments, including a downward-looking Riegl laser rangefinder mounted on the foremast of the R/V Sikuliaq. Although time series measurements on a stationary vessel are thought to be accurate, an underway vessel introduces a Doppler shift to the observed wave spectrum. This Doppler shift is a function of the wavenumber vector and the velocity vector of the vessel. Of all the possible relative angles between wave direction and vessel heading, there are two main scenarios: 1) vessel steaming into waves and 2) vessel steaming with waves. Previous studies have considered only a subset of cases, and all were in scenario 1. This was likely to avoid ambiguities, which arise when the vessel is steaming with waves. This study addresses the ambiguities and analyzes arbitrary cases. In addition, a practical method is provided that is useful in situations when the vessel is changing speed or heading. These methods improved the laser rangefinder estimates of spectral shapes and peak parameters when compared to nearby buoys and a spectral wave model. C. O. Collins B. W. Blomquist P. O. G. Persson B. Lund W. E. Rogers J. Thomson D. Wang M. Smith M. Doble P. Wadams A. Kohout C. W. Fairall H. C. Graber 2014-01-09T01:01:04Z 2014-01-09T01:01:04Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1012 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1012 2014-01-09T01:01:04Z Statistics of Storm Updraft Velocities from TWP-ICE Including Verification with Profiling Measurements Comparisons between direct measurements and modeled values of vertical air motions in precipitating systems are complicated by differences in temporal and spatial scales. On one hand, vertically profiling radars more directly measure the vertical air motion but do not adequately capture full storm dynamics. On the other hand, vertical air motions retrieved from two or more scanning Doppler radars capture the full storm dynamics but require model constraints that may not capture all updraft features because of inadequate sampling, resolution, numerical constraints, and the fact that the storm is evolving as it is scanned by the radars. To investigate the veracity of radar-based retrievals, which can be used to verify numerically modeled vertical air motions, this article presents several case studies from storm events around Darwin, Northern Territory, Australia, in which measurements from a dual-frequency radar profiler system and volumetric radar-based wind retrievals are compared. While a direct comparison was not possible because of instrumentation location, an indirect comparison shows promising results, with volume retrievals comparing well to those obtained from the profiling system. This prompted a statistical analysis of an extended period of an active monsoon period during the Tropical Warm Pool International Cloud Experiment (TWP-ICE). Results show less vigorous deep convective cores with maximum updraft velocities occurring at lower heights than some cloud-resolving modeling studies suggest. S. Collis A. Protat P. T. May C. R. Williams 2014-01-08T20:48:41Z 2014-07-24T22:08:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/983 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/983 2014-01-08T20:48:41Z Coupled mode transport theory for sound transmission through an ocean with random sound speed perturbations: Coherence in deep water environments Second moments of mode amplitudes at fixed frequency as a function of separations in mode number, time, and horizontal distance are investigated using mode-based transport equations and Monte Carlo simulation. These second moments are used to study full-field acoustic coherence, including depth separations. Calculations for low-order modes between 50 and 250 Hz are presented using a deep-water Philippine Sea environment. Comparisons between Monte Carlo simulations and transport theory for time and depth coherence at frequencies of 75 and 250 Hz and for ranges up to 500 km show good agreement. The theory is used to examine the accuracy of the adiabatic and quadratic lag approximations, and the range and frequency scaling of coherence. It is found that while temporal coherence has a dominant adiabatic component, horizontal and vertical coherence have more equal contributions from coupling and adiabatic effects. In addition, the quadratic lag approximation is shown to be most accurate at higher frequencies and longer ranges. Last the range and frequency scalings are found to be sensitive to the functional form of the exponential decay of coherence with lag, but temporal and horizontal coherence show scalings that fall quite close to the well-known inverse frequency and inverse square root range laws. J. A. Colosi T. K. Chandrayadula A. G. Voronovich V. E. Ostashev 2012-10-01T16:57:39Z 2013-04-24T20:30:46Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/284 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/284 2012-10-01T16:57:39Z Oceanic influences on recent continental warming Evidence is presented that the recent worldwide land warming has occurred largely in response to a worldwide warming of the oceans rather than as a direct response to increasing greenhouse gases (GHGs) over land. Atmospheric model simulations of the last half-century with prescribed observed ocean temperature changes, but without prescribed GHG changes, account for most of the land warming. The oceanic influence has occurred through hydrodynamic-radiative teleconnections, primarily by moistening and warming the air over land and increasing the downward longwave radiation at the surface. The oceans may themselves have warmed from a combination of natural and anthropogenic influences. G. P. Compo P. D. Sardeshmukh 2012-09-26T16:02:47Z 2013-05-07T19:56:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/220 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/220 2012-09-26T16:02:47Z Removing ENSO-Related Variations from the Climate Record An important question in assessing twentieth-century climate change is to what extent have ENSO-related variations contributed to the observed trends. Isolating such contributions is challenging for several reasons, including ambiguities arising from how ENSO itself is defined. In particular, defining ENSO in terms of a single index and ENSO-related variations in terms of regressions on that index, as done in many previous studies, can lead to wrong conclusions. This paper argues that ENSO is best viewed not as a number but as an evolving dynamical process for this purpose. Specifically, ENSO is identified with the four dynamical eigenvectors of tropical SST evolution that are most important in the observed evolution of ENSO events. This definition is used to isolate the ENSO-related component of global SST variations on a month-by-month basis in the 136-yr (1871–2006) Hadley Centre Sea Ice and Sea Surface Temperature dataset (HadISST). The analysis shows that previously identified multidecadal variations in the Pacific, Indian, and Atlantic Oceans all have substantial ENSO components. The long-term warming trends over these oceans are also found to have appreciable ENSO components, in some instances up to 40% of the total trend. The ENSO-unrelated component of 5-yr average SST variations, obtained by removing the ENSO-related component, is interpreted as a combination of anthropogenic, naturally forced, and internally generated coherent multidecadal variations. The following two surprising aspects of these ENSO-unrelated variations are emphasized: 1) a strong cooling trend in the eastern equatorial Pacific Ocean and 2) a nearly zonally symmetric multidecadal tropical–extratropical seesaw that has amplified in recent decades. The latter has played a major role in modulating SSTs over the Indian Ocean. G. P. Compo P. D. Sardeshmukh 2013-08-26T22:00:29Z 2013-08-26T22:00:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/944 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/944 2013-08-26T22:00:29Z Independent confirmation of global land warming without the use of station temperatures Confidence in estimates of anthropogenic climate change is limited by known issues with air temperature observations from land stations. Station siting, instrument changes, changing observing practices, urban effects, land cover, land use variations, and statistical processing have all been hypothesized as affecting the trends presented by the Intergovernmental Panel on Climate Change and others. Any artifacts in the observed decadal and centennial variations associated with these issues could have important consequences for scientific understanding and climate policy. We use a completely different approach to investigate global land warming over the 20th century. We have ignored all air temperature observations and instead inferred them from observations of barometric pressure, sea surface temperature, and sea-ice concentration using a physically based data assimilation system called the 20th Century Reanalysis. This independent data set reproduces both annual variations and centennial trends in the temperature data sets, demonstrating the robustness of previous conclusions regarding global warming. G. P. Compo P. D. Sardeshmukh J. S. Whitaker P. Brohan P. D. Jones C. McColl 2012-09-23T02:10:09Z 2013-05-10T20:09:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/114 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/114 2012-09-23T02:10:09Z Feasibility of a 100-year reanalysis using only surface pressure data Climate variability and global change studies are increasingly focused on understanding and predicting regional changes of daily weather statistics. Assessing the evidence for such variations over the last 100 yr requires a daily tropospheric circulation dataset. The only dataset available for the early twentieth century consists of error-ridden hand-drawn analyses of the mean sea level pressure field over the Northern Hemisphere. Modern data assimilation systems have the potential to improve upon these maps, but prior to 1948, few digitized upper-air sounding observations are available for such a "reanalysis." We investigate the possibility that the additional number of newly recovered surface pressure observations is sufficient to generate useful weather maps of the lower-tropospheric extratropical circulation back to 1890 over the Northern Hemisphere, and back to 1930 over the Southern Hemisphere. Surprisingly, we find that by using an advanced data assimilation system based on an ensemble Kalman filter, it would be feasible to produce high-quality maps of even the upper troposphere using only surface pressure observations. For the beginning of the twentieth century, the errors of such upper-air circulation maps over the Northern Hemisphere in winter would be comparable to the 2–3-day errors of modern weather forecasts. G. P. Compo J. S. Whitaker P. D. Sardeshmukh 2012-11-13T17:50:08Z 2013-05-02T16:30:31Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/622 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/622 2012-11-13T17:50:08Z The Twentieth Century Reanalysis Project The Twentieth Century Reanalysis (20CR) project is an international effort to produce a comprehensive global atmospheric circulation dataset spanning the twentieth century, assimilating only surface pressure reports and using observed monthly sea-surface temperature and sea-ice distributions as boundary conditions. It is chiefly motivated by a need to provide an observational dataset with quantified uncertainties for validations of climate model simulations of the twentieth century on all time-scales, with emphasis on the statistics of daily weather. It uses an Ensemble Kalman Filter data assimilation method with background 'first guess' fields supplied by an ensemble of forecasts from a global numerical weather prediction model. This directly yields a global analysis every 6 hours as the most likely state of the atmosphere, and also an uncertainty estimate of that analysis. The 20CR dataset provides the first estimates of global tropospheric variability, and of the dataset's time-varying quality, from 1871 to the present at 6-hourly temporal and 2° spatial resolutions. Intercomparisons with independent radiosonde data indicate that the reanalyses are generally of high quality. The quality in the extratropical Northern Hemisphere throughout the century is similar to that of current three-day operational NWP forecasts. Intercomparisons over the second half-century of these surface-based reanalyses with other reanalyses that also make use of upper-air and satellite data are equally encouraging. It is anticipated that the 20CR dataset will be a valuable resource to the climate research community for both model validations and diagnostic studies. Some surprising results are already evident. For instance, the long-term trends of indices representing the North Atlantic Oscillation, the tropical Pacific Walker Circulation, and the Pacific–North American pattern are weak or non-existent over the full period of record. The long-term trends of zonally averaged precipitation minus evaporation also differ in character from those in climate model simulations of the twentieth century. G. P. Compo J. S. Whitaker P. D. Sardeshmukh N. Matsui . . . S. D. Woodruff S. J. Worley 2012-10-15T23:23:49Z 2013-05-07T17:27:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/298 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/298 2012-10-15T23:23:49Z An Intercomparison of Microphysical Retrieval Algorithms for Upper-Tropospheric Ice Clouds The large horizontal extent, with its location in the cold upper troposphere, and ice composition make cirrus clouds important modulators of the Earth's radiation budget and climate. Cirrus cloud microphysical properties are difficult to measure and model because they are inhomogeneous in nature and their ice crystal size distribution and habit are not well characterized. Accurate retrievals of cloud properties are crucial for improving the representation of cloud-scale processes in large-scale models and for accurately predicting the Earth's future climate. A number of passive and active remote sensing retrieval algorithms exist for estimating the microphysical properties of upper-tropospheric clouds. We believe significant progress has been made in the evolution of these retrieval algorithms in the last decade; however, there is room for improvement. Members of the Atmospheric Radiation Measurement (ARM) program Cloud Properties Working Group are involved in an intercomparison of optical depth (τ) and ice water path in ice clouds retrieved using ground-based instruments. The goals of this intercomparison are to evaluate the accuracy of state-of-the-art algorithms, quantify the uncertainties, and make recommendations for their improvement. Currently, there are significant discrepancies among the algorithms for ice clouds with very small optical depths (τ < 0.3) and those with 1 < τ < 5. The good news is that for thin clouds (0.3 < τ < 1), the algorithms tend to converge. In this first stage of the intercomparison, we present results from a representative case study, compare the retrieved cloud properties with aircraft and satellite measurements, and perform a radiative closure experiment to begin gauging the accuracy of these retrieval algorithms. J. M. Comstock R. d'Entremont D. DeSlover G. G. Mace S. Y. Matrosov S. A. McFarlane P. Minnis D. Mitchell K. Sassen M. D. Shupe D. D. Turner Z. Wang 2017-05-05T19:47:22Z 2017-05-05T19:47:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1491 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1491 2017-05-05T19:47:22Z Development of a Coastal Drought Index Using Salinity Data A critical aspect of the uniqueness of coastal drought is the effects on the salinity dynamics of creeks, rivers, and estuaries. The location of the freshwater–saltwater interface along the coast is an important factor in the ecological and socioeconomic dynamics of coastal communities. Salinity is a critical response variable that integrates hydrologic and coastal dynamics including sea level, tides, winds, precipitation, streamflow, and tropical storms. The position of the interface determines the composition of freshwater and saltwater aquatic communities as well as the freshwater availability for water intakes. Many definitions of drought have been proposed, with most describing a decline in precipitation having negative impacts on the water supply. Indices have been developed incorporating data such as rainfall, streamflow, soil moisture, and groundwater levels. These water-availability drought indices were developed for upland areas and may not be ideal for characterizing coastal drought. The availability of real-time and historical salinity datasets provides an opportunity for the development of a salinity-based coastal drought index. An approach similar to the standardized precipitation index (SPI) was modified and applied to salinity data obtained from sites in South Carolina and Georgia. Using the SPI approach, the index becomes a coastal salinity index (CSI) that characterizes coastal salinity conditions with respect to drought periods of higher-saline conditions and wet periods of higher-freshwater conditions. Evaluation of the CSI indicates that it provides additional coastal response information as compared to the SPI and the Palmer hydrologic drought index, and the CSI can be used for different estuary types and for comparison of conditions along coastlines. P. A. Conrads L. S. Darby 2012-10-15T23:23:57Z 2013-05-07T17:28:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/299 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/299 2012-10-15T23:23:57Z Evidence for a recurring eastern North America upper tropospheric ozone maximum during summer Daily ozonesondes were launched from 14 North American sites during August 2006, providing the best set of free tropospheric ozone measurements ever gathered across the continent in a single season. The data reveal a distinct upper tropospheric ozone maximum above eastern North America and centered over the southeastern USA. Recurring each year, the location and strength of the ozone maximum is influenced by the summertime upper tropospheric anticyclone that traps convectively lofted ozone, ozone precursors and lightning NOx above the southeastern USA. The North American summer monsoon that flows northward along the Rocky Mountains is embedded within the western side of the anticyclone and also marks the westernmost extent of the ozone maximum. Removing the influence from stratospheric intrusions, median ozone mixing ratios (78 ppbv) in the upper troposphere (>6 km) above Alabama, near the center of the anticyclone, were nearly twice the level above the U.S. west coast. Simulations by an atmospheric chemistry general circulation model indicate lightning NOx emissions led to the production of 25–30 ppbv of ozone at 250 hPa above the southern United States during the study period. On the regional scale the ozone enhancement above the southeastern United States produced a positive all-sky adjusted radiative forcing up to 0.50 W m−2. O. R. Cooper M. Trainer . . . D. Wolfe et al. 2012-11-09T21:01:39Z 2013-05-08T15:38:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/597 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/597 2012-11-09T21:01:39Z Extreme changes in stable hydrogen isotopes and precipitation characteristics in a landfalling Pacific storm With a new automated precipitation collector we measured a remarkable decrease of 51‰ in the hydrogen isotope ratio (δ2H) of precipitation over a 60-minute period during the landfall of an extratropical cyclone along the California coast on 21 March 2005. The rapid drop in δ2H occurred as precipitation generation transitioned from a shallow to a much deeper cloud layer, in accord with synoptic-scale ascent and deep "seeder-feeder" precipitation. Such unexpected δ2H variations can substantially impact widely used isotope-hydrograph methods. From extreme δ2H values of −26 and −78‰, we calculate precipitation temperatures of 9.7 and −4.2°C using an adiabatic condensation isotope model, in good agreement with temperatures estimated from surface observations and radar data. This model indicates that 60 percent of the moisture was precipitated during ascent as temperature decreased from 15°C at the ocean surface to −4°C above the measurement site. T. B. Coplen P. J. Neiman A. B. White et al. 2014-07-15T19:58:24Z 2014-07-15T19:58:24Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1063 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1063 2014-07-15T19:58:24Z The Development and Evolution of Two Atmospheric Rivers in Proximity to Western North Pacific Tropical Cyclones in October 2010 This study investigates the evolution of two zonally elongated atmospheric rivers (ARs) that produced >200 mm of rainfall over mountainous regions of Northern California in late October 2010. Synoptic-scale analysis and air parcel trajectory analysis indicate that the ARs developed within high-CAPE environments characterized by troposphere-deep ascent as water vapor was transported directly from western North Pacific tropical cyclones (TCs) toward the equatorward entrance region of an intensifying North Pacific jet stream (NPJ). The same ARs were subsequently maintained as water vapor was transported from extratropical and subtropical regions over the central and eastern North Pacific in an environment characterized by quasigeostrophic forcing for ascent and strong frontogenesis along the anticyclonic shear side of an intense and zonally extended NPJ. Although the ARs developed in conjunction with water vapor transported from regions near TCs and in the presence of troposphere-deep ascent, an atmospheric water vapor budget illustrates that decreases in integrated water vapor (IWV) via precipitation are largely offset by the horizontal aggregation of water vapor along the AR corridors via IWV flux convergence in the presence of frontogenesis. The frameworks used for investigations of predecessor rain events ahead of TCs and of interactions between recurving TCs and the NPJ are also utilized to illustrate many dynamically similar processes related to AR development and evolution. Similarities include the following: water vapor transport directly from a TC, troposphere-deep ascent in a high-CAPE environment beneath the equatorward entrance region of an intensifying upper-tropospheric jet streak, interactions between diabatic outflow and an upper-tropospheric jet streak, and strong frontogenesis. J. M. Cordeira F. M. Ralph B. J. Moore 2016-10-13T23:01:08Z 2016-10-13T23:01:08Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1400 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1400 2016-10-13T23:01:08Z A synthetic data set of high-spectral-resolution infrared spectra for the Arctic atmosphere Cloud microphysical and macrophysical properties are critical for understanding the role of clouds in climate. These properties are commonly retrieved from ground-based and satellite-based infrared remote sensing instruments. However, retrieval uncertainties are difficult to quantify without a standard for comparison. This is particularly true over the polar regions, where surface-based data for a cloud climatology are sparse, yet clouds represent a major source of uncertainty in weather and climate models. We describe a synthetic high-spectral-resolution infrared data set that is designed to facilitate validation and development of cloud retrieval algorithms for surface- and satellite-based remote sensing instruments. Since the data set is calculated using pre-defined cloudy atmospheres, the properties of the cloud and atmospheric state are known a priori. The atmospheric state used for the simulations is drawn from radiosonde measurements made at the North Slope of Alaska (NSA) Atmospheric Radiation Measurement (ARM) site at Barrow, Alaska (71.325° N, 156.615° W), a location that is generally representative of the western Arctic. The cloud properties for each simulation are selected from statistical distributions derived from past field measurements. Upwelling (at 60 km) and downwelling (at the surface) infrared spectra are simulated for 260 cloudy cases from 50 to 3000 cm−1 (3.3 to 200 µm) at monochromatic (line-by-line) resolution at a spacing of ∼ 0.01 cm−1 using the Line-by-line Radiative Transfer Model (LBLRTM) and the discrete-ordinate-method radiative transfer code (DISORT). These spectra are freely available for interested researchers from the NSF Arctic Data Center data repository (doi:10.5065/D61J97TT). C. J. Cox P. M. Rowe S. P. Neshyba V. P. Walden 2014-07-24T22:10:55Z 2014-07-24T22:10:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1114 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1114 2014-07-24T22:10:55Z Cloud Microphysical Properties Retrieved from Downwelling Infrared Radiance Measurements Made at Eureka, Nunavut, Canada (2006–09) The radiative properties of clouds are related to cloud microphysical and optical properties, including water path, optical depth, particle size, and thermodynamic phase. Ground-based observations from remote sensors provide high-quality, long-term, continuous measurements that can be used to obtain these properties. In the Arctic, a more comprehensive understanding of cloud microphysics is important because of the sensitivity of the Arctic climate to changes in radiation. Eureka, Nunavut (80°N, 86°25′W, 10 m), Canada, is a research station located on Ellesmere Island. A large suite of ground-based remote sensors at Eureka provides the opportunity to make measurements of cloud microphysics using multiple instruments and methodologies. In this paper, cloud microphysical properties are presented using a retrieval method that utilizes infrared radiances obtained from an infrared spectrometer at Eureka between March 2006 and April 2009. These retrievals provide a characterization of the microphysics of ice and liquid in clouds with visible optical depths between 0.25 and 6, which are a class of clouds whose radiative properties depend greatly on their microphysical properties. The results are compared with other studies that use different methodologies at Eureka, providing context for multimethod perspectives. The authors' findings are supportive of previous studies, including seasonal cycles in phase and liquid particle size, weak temperature–phase dependencies, and frequent occurrences of supercooled water. Differences in microphysics are found between mixed-phase and single-phase clouds for both ice and liquid. The Eureka results are compared with those obtained using a similar retrieval technique during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment. C. J. Cox D. D. Turner P. M. Rowe M. D. Shupe V. P. Walden 2016-10-13T22:59:07Z 2016-10-13T22:59:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1399 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1399 2016-10-13T22:59:07Z The Role of Springtime Arctic Clouds in Determining Autumn Sea Ice Extent Recent studies suggest that the atmosphere conditions arctic sea ice properties in spring in a way that may be an important factor in predetermining autumn sea ice concentrations. Here, the role of clouds in this system is analyzed using surface-based observations from Barrow, Alaska. Barrow is a coastal location situated adjacent to the region where interannual sea ice variability is largest. Barrow is also along a main transport pathway through which springtime advection of atmospheric energy from lower latitudes to the Arctic Ocean occurs. The cloud contribution is quantified using the observed surface radiative fluxes and cloud radiative forcing (CRF) derived therefrom, which can be positive or negative. In low sea ice years enhanced positive CRF (increased cloud cover enhancing longwave radiative forcing) in April is followed by decreased negative CRF (decreased cloud cover allowing a relative increase in shortwave radiative forcing) in May and June. The opposite is true in high sea ice years. In either case, the combination and timing of these early and late spring cloud radiative processes can serve to enhance the atmospheric preconditioning of sea ice. The net CRF (April and May) measured at Barrow from 1993 through 2014 is negatively correlated with sea ice extent in the following autumn (r2 = 0.33; p < 0.01). Reanalysis data appear to capture the general timing and sign of the observed CRF anomalies at Barrow and suggest that the anomalies occur over a large region of the central Arctic Ocean, which supports the link between radiative processes observed at Barrow and the broader arctic sea ice extent. C. J. Cox T. Uttal C. N. Long M. D. Shupe R. S. Stone S. M. Starkweather 2015-04-24T20:30:35Z 2015-10-07T15:29:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1157 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1157 2015-04-24T20:30:35Z Downwelling longwave flux over Summit, Greenland, 2010–2012: Analysis of surface-based observations and evaluation of ERA-Interim using wavelets This study analyzes the downwelling longwave radiation (DLW) over the Greenland Ice Sheet (GrIS) using surface-based observations from Summit Station (72°N, 38°W; 3210 m) and the European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim) DLW fields. Since surface-based observations are sparse in the Arctic, the accuracy of including reanalyses for spatial context is assessed. First, the DLW at Summit is reported, including the significant time scales of variability using time-frequency decomposition (wavelet analysis). A new method for evaluating reanalyses is then introduced that also uses wavelet analysis. ERA-Interim DLW performs reasonably well at Summit, but because it includes too many thin clouds and too few thick clouds, it is biased low overall. The correlation between the observations and ERA-Interim drops from r2 > 0.8 to near 0 for time series reconstructed from time scales less than ~4 days. These low correlations and additional analyses suggest that the spatial resolution of the data sets is a factor in representing variability on short time scales. The bias is low across all time scales and is thus likely tied to cloud generation processes in the model rather than the spatial representation of the atmosphere across the GrIS. The exception is autumn, when ERA-Interim overestimates the influence of clouds at time scales of 1 and 4 weeks. The spatial distribution of cloud influence on the DLW across the GrIS indicates that Summit is located in a transition zone with respect to cloud properties. The gradient across this transition zone is steepest near Summit in autumn, so the spatial characteristics of the atmosphere near Summit may contribute to the ERA-Interim bias during this time. C. J. Cox V. P. Walden G. P. Compo P. M. Rowe M. D. Shupe K. Steffen 2015-12-18T18:03:43Z 2016-03-21T20:48:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1298 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1298 2015-12-18T18:03:43Z Humidity trends imply increased sensitivity to clouds in a warming Arctic Infrared radiative processes are implicated in Arctic warming and sea-ice decline. The infrared cloud radiative effect (CRE) at the surface is modulated by cloud properties; however, CRE also depends on humidity because clouds emit at wavelengths that are semi-transparent to greenhouse gases, most notably water vapour. Here we show how temperature and humidity control CRE through competing influences between the mid- and far-infrared. At constant relative humidity, CRE does not decrease with increasing temperature/absolute humidity as expected, but rather is found to be approximately constant for temperatures characteristic of the Arctic. This stability is disrupted if relative humidity varies. Our findings explain observed seasonal and regional variability in Arctic CRE of order 10 W m−2. With the physical properties of Arctic clouds held constant, we calculate recent increases in CRE of 1–5 W m−2 in autumn and winter, which are projected to reach 5–15 W m−2 by 2050, implying increased sensitivity of the surface to clouds. C. J. Cox V. P. Walden P. M. Rowe M. D. Shupe 2015-10-07T15:37:12Z 2015-10-07T15:37:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1231 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1231 2015-10-07T15:37:12Z The International Surface Pressure Databank version 2 The International Surface Pressure Databank (ISPD) is the world's largest collection of global surface and sea-level pressure observations. It was developed by extracting observations from established international archives, through international cooperation with data recovery facilitated by the Atmospheric Circulation Reconstructions over the Earth (ACRE) initiative, and directly by contributing universities, organizations, and countries. The dataset period is currently 1768–2012 and consists of three data components: observations from land stations, marine observing systems, and tropical cyclone best track pressure reports. Version 2 of the ISPD (ISPDv2) was created to be observational input for the Twentieth Century Reanalysis Project (20CR) and contains the quality control and assimilation feedback metadata from the 20CR. Since then, it has been used for various general climate and weather studies, and an updated version 3 (ISPDv3) has been used in the ERA-20C reanalysis in connection with the European Reanalysis of Global Climate Observations project (ERA-CLIM). The focus of this paper is on the ISPDv2 and the inclusion of the 20CR feedback metadata. The Research Data Archive at the National Center for Atmospheric Research provides data collection and access for the ISPDv2, and will provide access to future versions. T. A. Cram G. P. Compo X. Yin R. J. Allan C. McColl R. Vose J. S. Whitaker 2015-04-27T15:51:14Z 2015-10-07T15:45:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1160 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1160 2015-04-27T15:51:14Z Impact of interannual variations in aerosol particle sources on orographic precipitation over California's Central Sierra Nevada Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater field campaign (2009–2011), the variability and associated impacts of different aerosol sources on precipitation were investigated in the California Sierra Nevada using an aerosol time-of-flight mass spectrometer for precipitation chemistry, S-band profiling radar for precipitation classification, remote sensing measurements of cloud properties, and surface meteorological measurements. The composition of insoluble residues in precipitation samples collected at a surface site contained mostly local biomass burning and long-range transported dust and biological particles (2009), local sources of biomass burning and pollution (2010), and long-range transport from distant sources (2011). Although differences in the sources were observed from year-to-year, the most consistent source of dust and biological residues were associated with storms consisting of deep convective cloud systems with significant quantities of precipitation initiated in the ice phase. Further, biological residues were dominant (up to 40%) during storms with relatively warm cloud temperatures (up to −15 °C), supporting the important role bioparticles can play as ice nucleating particles. On the other hand, lower percentages of residues from local biomass burning and pollution were observed over the three winter seasons (on average 31 and 9%, respectively). When precipitation quantities were relatively low, these residues most likely served as CCN, forming smaller more numerous cloud droplets at the base of shallow cloud systems, and resulting in less efficient riming processes. The correlation between the source of aerosols within clouds and precipitation type and quantity will be further probed in models to understand the mechanisms by which local emissions vs. long-range transported dust and biological aerosols play roles in impacting regional precipitation processes. Ultimately, the goal is to use such observations to improve the mechanistic linkages between aerosol sources and precipitation processes to produce more accurate predictive weather forecast models and improve water resource management. J. M. Creamean A. P. Ault A. B. White P. J. Neiman F. M. Ralph P. Minnis K. A. Prather 2016-07-08T16:24:29Z 2016-07-13T22:26:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1366 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1366 2016-07-08T16:24:29Z Changes in precipitating snow chemistry with location and elevation in the California Sierra Nevada Orographic snowfall in the Sierra Nevada Mountains is an important source of water for California and can vary significantly on an annual basis. The microphysical properties of orographic clouds and subsequent formation of precipitation are impacted, in part, by aerosols of varying size, number, and chemical composition, which are incorporated into clouds formed along the Sierra barrier. Herein, the physicochemical properties and sources of insoluble residues and soluble ions found in precipitation samples were explored for three sites of variable elevation in the Sierra Nevada during the 2012–2013 winter season. Residues were characterized using a suite of physicochemical techniques to determine the size-resolved number concentrations and associated chemical composition. A transition in the aerosol sources that served as cloud seeds or were scavenged in-cloud and below-cloud was observed as a function of location and elevation. Anthropogenic influence from the Central Valley was dominant at the two lowest elevation sites (1900 and 2200 m above mean sea level (AMSL)), whereas long-range transported mineral dust was a larger contributor at the highest elevation site where cleaner conditions were observed (2600 m AMSL). The residues and soluble ions observed provide insight into how multiple aerosol sources can impact cloud and precipitation formation processes, even over relatively small spatial scales. The transition with increasing elevation to aerosols that serve as ice nucleating particles may impact the properties and extent of snowfall in remote mountain regions where snowpack provides a vital supply of water. J. M. Creamean J. L. Axson A. L. Bondy R. L. Craig N. W. May H. Shen M. H. Weber K. A. Pratt A. P. Ault 2014-07-24T22:15:49Z 2015-10-07T15:41:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1115 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1115 2014-07-24T22:15:49Z Chemical properties of insoluble precipitation residue particles Precipitation chemistry can provide unique insights into the composition of aerosol particles involved in precipitation processes. Until recently, precipitation chemistry studies focused predominantly on soluble components. Analyzing the single particle insoluble components in addition to soluble ions in precipitation can provide detailed information on the individual particles originally in the cloud or removed by precipitation as well as the source of the aerosols. Herein, we present an in-depth analysis of resuspended residues from precipitation samples collected at a remote site in the Sierra Nevada Mountains in California during the 2009–2011 winter seasons. In addition, we present results from laboratory control experiments of dust, leaf litter, smoke, and sea salt samples that were conducted to better understand how insoluble and soluble residues are distributed during the atomization process and aid in the classification of the residue compositions in the precipitation samples. Further, immersion freezing ice nuclei (IN) measurements of insoluble residues from precipitation water enabled the determination of residue types that likely seeded clouds. Long-range transported dust mixed with biological material tended to be more IN active, while purely biological residues contained a variety of high and low temperature IN. Overall, results from this study can be used as a benchmark for classification of insoluble precipitation residues in future studies. Knowledge of the precipitation chemistry of insoluble residues coupled with meteorological and cloud microphysical measurements will ultimately improve our understanding of the link between aerosols, clouds, and precipitation. J. M. Creamean C. Lee T. C. Hill A. P. Ault P. J. DeMott A. B. White F. M. Ralph K. A. Prather 2016-10-13T23:03:36Z 2016-10-13T23:03:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1401 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1401 2016-10-13T23:03:36Z Colorado air quality impacted by long-range-transported aerosol: a set of case studies during the 2015 Pacific Northwest fires Biomass burning plumes containing aerosols from forest fires can be transported long distances, which can ultimately impact climate and air quality in regions far from the source. Interestingly, these fires can inject aerosols other than smoke into the atmosphere, which very few studies have evidenced. Here, we demonstrate a set of case studies of long-range transport of mineral dust aerosols in addition to smoke from numerous fires (including predominantly forest fires and a few grass/shrub fires) in the Pacific Northwest to Colorado, US. These aerosols were detected in Boulder, Colorado, along the Front Range using beta-ray attenuation and energy-dispersive X-ray fluorescence spectroscopy, and corroborated with satellite-borne lidar observations of smoke and dust. Further, we examined the transport pathways of these aerosols using air mass trajectory analysis and regional- and synoptic-scale meteorological dynamics. Three separate events with poor air quality and increased mass concentrations of metals from biomass burning (S and K) and minerals (Al, Si, Ca, Fe, and Ti) occurred due to the introduction of smoke and dust from regional- and synoptic-scale winds. Cleaner time periods with good air quality and lesser concentrations of biomass burning and mineral metals between the haze events were due to the advection of smoke and dust away from the region. Dust and smoke present in biomass burning haze can have diverse impacts on visibility, health, cloud formation, and surface radiation. Thus, it is important to understand how aerosol populations can be influenced by long-range-transported aerosols, particularly those emitted from large source contributors such as wildfires. J. M. Creamean P. J. Neiman T. Coleman C. J. Senff G. Kirgis R. J. Alvarez A. Yamamoto 2015-04-27T15:47:50Z 2015-10-07T15:43:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1159 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1159 2015-04-27T15:47:50Z Climatology of long-range transported Asian dust along the West Coast of the United States The contribution of trans-Pacific dust estimated from satellite observations has been shown to be 3 times greater than domestic dust in North America throughout the year. Thus, a quantitative understanding of the frequency and locations where Asian dust is transported is necessary to improve global dust modeling for weather and climate predictions. This work presents a 10 year record (2002–2011) of dust along the U.S. West Coast estimated from the Interagency Monitoring of Protected Visual Environments network in an effort to characterize the seasonal cycle and interannual variability of Asian dust transport. In addition, observations of dust exported from East Asia were analyzed along with air mass trajectories and satellite and ground-based precipitation data to investigate seasonal variability of Asian dust transport. On average, Asian dust concentrations (0.08–0.60 µg m−3) from ground-based observations were 1.7 times those of local dust (0.00–0.53 µg m−3) and 23% (up to 44%) of fine particulate matter (particles with diameters ≤ 2.5 micrometers, or PM2.5) mass concentrations at high elevations in the spring. The maximum in springtime Asian dust on the U.S. West Coast was attributed to higher source concentrations (10.98–36.27 µg m−3) and reduced potential for wet removal over the Pacific Ocean and U.S. West Coast. Although trans-Pacific transport was more favorable during the winter, minimum concentrations of Asian dust were observed on the U.S. West Coast (0.11 µg m−3) due to a lower source influence and higher potential for wet removal during transport. Multiobservational approaches such as these should be taken into account when modeling transport of Asian dust to the western U.S. J. M. Creamean J. R. Spackman S. Davis A. B. White 2013-04-16T16:16:16Z 2013-04-24T17:27:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/905 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/905 2013-04-16T16:16:16Z Dust and Biological Aerosols from the Sahara and Asia Influence Precipitation in the Western U.S. Winter storms in California's Sierra Nevada increase seasonal snowpack and provide critical water resources and hydropower for the state. Thus, the mechanisms influencing precipitation in this region have been the subject of research for decades. Previous studies suggest Asian dust enhances cloud ice and precipitation, whereas few studies consider biological aerosols as an important global source of ice nuclei (IN). Here, we show that dust and biological aerosols transported from as far as the Sahara were present in glaciated high-altitude clouds coincident with elevated IN concentrations and ice-induced precipitation. This study presents the first direct cloud and precipitation measurements showing that Saharan and Asian dust and biological aerosols probably serve as IN and play an important role in orographic precipitation processes over the western United States. J. M. Creamean K. J. Suski D. Rosenfeld A. Cazorla P. J. DeMott R. C. Sullivan A. B. White F. M. Ralph et al. 2016-07-08T16:28:53Z 2016-07-08T16:28:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1365 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1365 2016-07-08T16:28:53Z The relationships between insoluble precipitation residues, clouds, and precipitation over California's southern Sierra Nevada during winter storms Ice formation in orographic mixed-phase clouds can enhance precipitation and depends on the type of aerosols that serve as ice nucleating particles (INPs). The resulting precipitation from these clouds is a viable source of water, especially for regions such as the California Sierra Nevada. Thus, a better understanding of the sources of INPs that impact orographic clouds is important for assessing water availability in California. This study presents a multi-site, multi-year analysis of single-particle insoluble residues in precipitation samples that likely influenced cloud ice and precipitation formation above Yosemite National Park. Dust and biological particles represented the dominant fraction of the residues (64% on average). Cloud glaciation, determined using satellite observations, not only depended on high cloud tops (>5.9 km) and low temperatures (<−23 °C), but also on the presence of what were likely dust and biological INPs. The greatest prevalence of ice-phase clouds occurred in conjunction with biologically-rich residues and mineral dust rich in calcium, followed by iron and aluminosilicates. Dust and biological particles are known to be efficient INPs, thus these residues likely influenced ice formation in clouds above the sites and subsequent precipitation quantities reaching the surface during events with similar meteorology. The goal of this study is to use precipitation chemistry information to gain a better understanding of the potential sources of INPs in the south-central Sierra Nevada, where cloud-aerosol-precipitation interactions are poorly understood and where mixed-phase orographic clouds represent a key element in the generation of precipitation and thus the water supply in California. J. M. Creamean A. B. White P. Minnis R. Palikonda D. A. Spangenberg K. A. Prather 2012-09-23T02:13:44Z 2013-05-13T15:20:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/115 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/115 2012-09-23T02:13:44Z Surface Cloud Forcing in the East Pacific Stratus Deck/Cold Tongue/ITCZ Complex Data from the Eastern Pacific Investigation of Climate Studies (EPIC) mooring array are used to evaluate the annual cycle of surface cloud forcing in the far eastern Pacific stratus cloud deck/cold tongue/intertropical convergence zone complex. Data include downwelling surface solar and longwave radiation from 10 EPIC-enhanced Tropical Atmosphere Ocean (TAO) moorings from 8°S, 95°W to 12°N, 95°W, and the Woods Hole Improved Meteorology (IMET) mooring in the stratus cloud deck region at 20°S, 85°W. Surface cloud forcing is defined as the observed downwelling radiation at the surface minus the clear-sky value. Solar cloud forcing and longwave cloud forcing are anticorrelated at all latitudes from 12°N to 20°S: clouds tended to reduce the downward solar radiation and to a lesser extent increase the downward longwave radiation at the surface. The relative amount of solar radiation reduction and longwave increase depends upon cloud type and varies with latitude. A statistical relationship between solar and longwave surface cloud forcing is developed for rainy and dry periods and for the full record length in six latitudinal regions: northeast tropical warm pool, ITCZ, frontal zone, cold tongue, southern, and stratus deck regions. The buoy cloud forcing observations and empirical relations are compared with the International Satellite Cloud Climatology Project (ISCCP) radiative flux data (FD) dataset and are used as benchmarks to evaluate surface cloud forcing in the NCEP Reanalysis 2 (NCEP2) and 40-yr ECMWF Re-Analysis (ERA-40). ERA-40 and NCEP2 cloud forcing (both solar and longwave) showed large discrepancies with observations, being too large in the ITCZ and equatorial regions and too weak under the stratus deck at 20°S and north to the equator during the cool season from July to December. In particular the NCEP2 cloud forcing at the equator was nearly identical to the ITCZ region and thus had significantly larger solar cloud forcing and smaller longwave cloud forcing than observed. The net result of the solar and longwave cloud forcing deviations is that there is too little radiative warming in the ITCZ and southward to 8°S during the warm season and too much radiative warming under the stratus deck at 20°S and northward to the equator during the cold season. M. F. Cronin N. A. Bond C. W. Fairall R. A. Weller 2012-09-23T02:16:39Z 2013-05-10T20:29:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/116 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/116 2012-09-23T02:16:39Z An assessment of buoy-derived and numerical weather prediction surface heat fluxes in the tropical Pacific As part of the Eastern Pacific Investigation of Climate Processes program, from 2000 through 2003, the easternmost 95°W Tropical Atmosphere Ocean (TAO) moorings were enhanced to provide time series of net surface heat flux, and the National Oceanic and Atmospheric Administration ship maintaining the 95°W and 110°W TAO lines was enhanced to monitor surface heat fluxes and atmospheric boundary layer structure. In this study we compare the ship-based and buoy-based radiative, bulk latent, and sensible heat fluxes, as well as the meteorological state variables used to compute the turbulent heat fluxes. The buoy net surface heat flux measurements appear to have an overall uncertainty near the target 10 W m−2, when careful attention is paid to the state variables. When hourly averaged data were unavailable, the telemetered daily averaged data were used in combination with an estimate of the mesoscale gustiness. In the eastern tropical Pacific a warm layer correction to account for stratification above 1-m depth was important only during the warm season (January–May) near the equator. These high-quality, cross-validated buoy heat flux time series are then used to assess the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), NCEP/Department of Energy, and 40-year European Centre for Medium-Range Weather Forecasts reanalyses' surface heat fluxes. All reanalyses show that over warm water where deep convection is prominent, latent heat loss is too large and net solar radiation is too weak; conversely, in regions of stratocumulus over cool water, net solar radiation is too strong, and for NCEP/NCAR, latent heat loss is too weak. M. F. Cronin C. W. Fairall M. J. McPhaden 2012-11-06T18:44:55Z 2013-05-13T15:44:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/491 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/491 2012-11-06T18:44:55Z Multifunctional mesoscale observing networks More than 120 scientists, engineers, administrators, and users met on 8–10 December 2003 in a workshop format to discuss the needs for enhanced three-dimensional mesoscale observing networks. Improved networks are seen as being critical to advancing numerical and empirical modeling for a variety of mesoscale applications, including severe weather warnings and forecasts, hydrology, air-quality forecasting, chemical emergency response, transportation safety, energy management, and others. The participants shared a clear and common vision for the observing requirements: existing two-dimensional mesoscale measurement networks do not provide observations of the type, frequency, and density that are required to optimize mesoscale prediction and nowcasts. To be viable, mesoscale observing networks must serve multiple applications, and the public, private, and academic sectors must all actively participate in their design and implementation, as well as in the creation and delivery of value-added products. The mesoscale measurement challenge can best be met by an integrated approach that considers all elements of an end-to-end solution—identifying end users and their needs, designing an optimal mix of observations, defining the balance between static and dynamic (targeted or adaptive) sampling strategies, establishing long-term test beds, and developing effective implementation strategies. Detailed recommendations are provided pertaining to nowcasting, numerical prediction and data assimilation, test beds, and implementation strategies. W. F. Dabberdt T. W. Schlatter F. H. Carr E. W. J. Friday D. Jorgensen S. Koch M. Pirone F. M. Ralph et al. 2012-09-23T02:23:35Z 2013-05-10T20:29:43Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/117 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/117 2012-09-23T02:23:35Z Cloud property estimates from zenith spectral measurements of scattered sunlight between 0.9 and 1.7 µm A theoretical approach is used to quantify the information available to retrieve cloud physical properties from data taken by a ground-based spectrometer measuring scattered sunlight in the near-infrared wavelength region. Three wavelength regions between 0.9 and 1.7 μm, each containing water vapor, liquid, and ice absorption features, are examined using a differential optical absorption spectroscopy optimal estimation retrieval technique. Cloud properties that can be retrieved include path-integrated liquid water path and path-integrated ice water path (PLWP and PIWP), cloud liquid and ice temperatures, and the second moment of the photon path distribution. The accuracy of these cloud property retrievals is estimated for a variety of simulated conditions, with key analysis assumptions identified. The sensitivity of the measurements in the longest wavelength region to liquid water and ice is high, allowing for accurate estimates of PLWP and PIWP under optically thin clouds, while the shorter two wavelength bands provide more information under optically thicker clouds. Observations of mixed-phase clouds over Barrow, Alaska, are used to illustrate the practicality of the technique. Retrieved LWP values (inferred from PLWP) are compared to LWP estimates from a microwave radiometer and an atmospheric emitted radiance interferometer; PIWP estimates are compared to IWP estimates from a millimeter-wave cloud radar. Cloud liquid temperature and photon path distribution information retrieved from these data are also presented. Furthermore, we suggest a technique for combining near-infrared spectral PLWP measurements with microwave radiometer observations to estimate cloud droplet effective radius. J. S. Daniel R. W. Portmann H. L. Miller S. Solomon A. O. Langford C. S. Eubank R. Schofield D. Turner M. D. Shupe 2012-10-15T23:24:04Z 2013-05-07T17:29:28Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/300 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/300 2012-10-15T23:24:04Z Ozone differences between near-coastal and offshore sites in New England: Role of meteorology Time series from two ozone monitoring stations are evaluated, one on an island several km off the New England coast, the other several km inland in New Hampshire. In the summer of 2002, during the New England Air Quality Study 2002 (NEAQS-2002), ozone measurements at the island station, Appledore Island (ADI), were consistently higher than at the inland station, Thompson Farm (TF). We hypothesized that the differences in ozone concentrations were due to transport differences driven by mesoscale meteorology, since neither site was in a source region. We found that the Appalachian Trough, coastal cold fronts and coastal stationary fronts at times caused TF to have westerly component flow while ADI had southerly component flow. In these situations, the southwesterly flow along the New England coast brought ozone and precursors to ADI from metropolitan areas to the southwest (e.g., Boston). Conversely, the air transported to TF from the west was contaminated by fewer upstream sources, and therefore the ozone was lower at TF. The sea breeze was also a factor, which tended to have the contrasting effect of nearly equalizing the ozone concentrations at the two sites by transporting ozone-rich air already impacting ADI inland to TF. Enhanced measurements from the NEAQS-2002 study were used in the analysis, including radar wind profilers, Doppler and ozone profiling lidars, and radiosondes launched from a ship. We also assessed model performance for two models, WRF/Chem and MM5/Chem, for four key days. L. S. Darby S. A. McKeen C. J. Senff A. B. White R. M. Banta M. J. Post W. A. Brewer R. Marchbanks R. J. Alvarez II S. E. Peckham H. Mao R. Talbot 2012-11-13T20:43:22Z 2013-05-08T15:38:41Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/645 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/645 2012-11-13T20:43:22Z A reassessment of Antarctic plateau reactive nitrogen based on ANTCI 2003 airborne and ground based measurements The first airborne measurements of nitric oxide (NO) on the Antarctic plateau have demonstrated that the previously reported elevated levels of this species extend well beyond the immediate vicinity of South Pole. Although the current database is still relatively weak and critical laboratory experiments are still needed, the findings here suggest that the chemical uniqueness of the plateau may be substantially greater than first reported. For example, South Pole ground-based findings have provided new evidence showing that the dominant process driving the release of nitrogen from the snowpack during the spring/summer season (post-depositional loss) is photochemical in nature with evaporative processes playing a lesser role. There is also new evidence suggesting that nitrogen, in the form of nitrate, may undergo multiple recycling within a given photochemical season. Speculation here is that this may be a unique property of the plateau and much related to its having persistent cold temperatures even during summer. These conditions promote the efficient adsorption of molecules like HNO3 (and very likely HO2NO2) onto snow-pack surface ice where we have hypothesized enhanced photochemical processing can occur, leading to the efficient release of NOx to the atmosphere. In addition, to these process-oriented tentative conclusions, the findings from the airborne studies, in conjunction with modeling exercises suggest a new paradigm for the plateau atmosphere. The near-surface atmosphere over this massive region can be viewed as serving as much more than a temporary reservoir or holding tank for imported chemical species. It defines an immense atmospheric chemical reactor which is capable of modifying the chemical characteristics of select atmospheric constituents. This reactor has most likely been in place over geological time, and may have led to the chemical modulation of some trace species now found in ice cores. Reactive nitrogen has played a critical role in both establishing and in maintaining this reactor. D. D. Davis J. Seelig . . . W. Neff et al. 2017-04-11T16:09:01Z 2017-04-11T16:09:01Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1469 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1469 2017-04-11T16:09:01Z Assessment of virtual towers performed with scanning wind lidars and Ka-band radars during the XPIA experiment During the eXperimental Planetary boundary layer Instrumentation Assessment (XPIA) campaign, which was carried out at the Boulder Atmospheric Observatory (BAO) in spring 2015, multiple-Doppler scanning strategies were carried out with scanning wind lidars and Ka-band radars. Specifically, step–stare measurements were collected simultaneously with three scanning Doppler lidars, while two scanning Ka-band radars carried out simultaneous range height indicator (RHI) scans. The XPIA experiment provided the unique opportunity to compare directly virtual-tower measurements performed simultaneously with Ka-band radars and Doppler wind lidars. Furthermore, multiple-Doppler measurements were assessed against sonic anemometer data acquired from the meteorological tower (met-tower) present at the BAO site and a lidar wind profiler. This survey shows that – despite the different technologies, measurement volumes and sampling periods used for the lidar and radar measurements – a very good accuracy is achieved for both remote-sensing techniques for probing horizontal wind speed and wind direction with the virtual-tower scanning technique. M. Debnath G. V. Iungo W. A. Brewer A. Choukulkar R. Delgado S. Gunter J. K. Lundquist J. L. Schroeder J. M. Wilczak D. E. Wolfe 2015-04-06T20:52:51Z 2015-10-06T21:45:56Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1119 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1119 2015-04-06T20:52:51Z The Use of Reanalysis Data for Monitoring the State of the Climate N/A D. Dee P. Berrisford M. G. Bosilovich M. Chelliah G. P. Compo . . . C. A. Smith R. Vose 2014-01-08T20:58:11Z 2014-01-08T20:58:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/985 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/985 2014-01-08T20:58:11Z Combined impacts of current and future dust deposition and regional warming on Colorado River Basin snow dynamics and hydrology The Colorado River provides water to 40 million people in seven western states and two countries and to 5.5 million irrigated acres. The river has long been overallocated. Climate models project runoff losses of 5–20% from the basin by mid-21st century due to human-induced climate change. Recent work has shown that decreased snow albedo from anthropogenic dust loading to the CO mountains shortens the duration of snow cover by several weeks relative to conditions prior to western expansion of the US in the mid-1800s, and advances peak runoff at Lees Ferry, Arizona, by an average of 3 weeks. Increases in evapotranspiration from earlier exposure of soils and germination of plants have been estimated to decrease annual runoff by more than 1.0 billion cubic meters, or ~5% of the annual average. This prior work was based on observed dust loadings during 2005–2008; however, 2009 and 2010 saw unprecedented levels of dust loading on snowpacks in the Upper Colorado River Basin (UCRB), being on the order of 5 times the 2005–2008 loading. Building on our prior work, we developed a new snow albedo decay parameterization based on observations in 2009/10 to mimic the radiative forcing of extreme dust deposition. We convolve low, moderate, and extreme dust/snow albedos with both historic climate forcing and two future climate scenarios via a delta method perturbation of historic records. Compared to moderate dust, extreme dust absorbs 2× to 4× the solar radiation, and shifts peak snowmelt an additional 3 weeks earlier to a total of 6 weeks earlier than pre-disturbance. The extreme dust scenario reduces annual flow volume an additional 1% (6% compared to pre-disturbance), a smaller difference than from low to moderate dust scenarios due to melt season shifting into a season of lower evaporative demand. The sensitivity of flow timing to dust radiative forcing of snow albedo is maintained under future climate scenarios, but the sensitivity of flow volume reductions decreases with increased climate forcing. These results have implications for water management and suggest that dust abatement efforts could be an important component of any climate adaptation strategies in the UCRB. J. S. Deems T. H. Painter J. J. Barsugli B. Udall 2014-01-09T17:21:14Z 2014-01-09T17:21:14Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1038 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1038 2014-01-09T17:21:14Z Lidar measurement of snow depth: a review Laser altimetry (lidar) is a remote-sensing technology that holds tremendous promise for mapping snow depth in snow hydrology and avalanche applications. Recently lidar has seen a dramatic widening of applications in the natural sciences, resulting in technological improvements and an increase in the availability of both airborne and ground-based sensors. Modern sensors allow mapping of vegetation heights and snow or ground surface elevations below forest canopies. Typical vertical accuracies for airborne datasets are decimeter-scale with order 1 m point spacings. Ground-based systems typically provide millimeter-scale range accuracy and sub-meter point spacing over 1 m to several kilometers. Many system parameters, such as scan angle, pulse rate and shot geometry relative to terrain gradients, require specification to achieve specific point coverage densities in forested and/or complex terrain. Additionally, snow has a significant volumetric scattering component, requiring different considerations for error estimation than for other Earth surface materials. We use published estimates of light penetration depth by wavelength to estimate radiative transfer error contributions. This paper presents a review of lidar mapping procedures and error sources, potential errors unique to snow surface remote sensing in the near-infrared and visible wavelengths, and recommendations for projects using lidar for snow-depth mapping. J. S. Deems T. H. Painter D. C. Finnegan 2012-09-26T16:23:07Z 2013-05-07T23:21:33Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/223 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/223 2012-09-26T16:23:07Z Sea surface Temperature Variability: Patterns and Mechanisms Patterns of sea surface temperature (SST) variability on interannual and longer timescales result from a combination of atmospheric and oceanic processes. These SST anomaly patterns may be due to intrinsic modes of atmospheric circulation variability that imprint themselves upon the SST field mainly via surface energy fluxes. Examples include SST fluctuations in the Southern Ocean associated with the Southern Annular Mode, a tripolar pattern of SST anomalies in the North Atlantic associated with the North Atlantic Oscillation, and a pan-Pacific mode known as the Pacific Decadal Oscillation (with additional contributions from oceanic processes). They may also result from coupled ocean-atmosphere interactions, such as the El Niño-Southern Oscillation phenomenon in the tropical Indo-Pacific, the tropical Atlantic Niño, and the cross-equatorial meridional modes in the tropical Pacific and Atlantic. Finally, patterns of SST variability may arise from intrinsic oceanic modes, notably the Atlantic Multidecadal Oscillation. C. Deser M. A. Alexander S.-P. Xie A. S. Phillips 2012-09-26T16:09:06Z 2013-05-07T23:15:05Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/222 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/222 2012-09-26T16:09:06Z Twentieth Century tropical sea surface temperature trends revisited This study compares the global distribution of 20th century SST and marine air temperature trends from a wide variety of data sets including un-interpolated archives as well as globally-complete reconstructions. Apart from the eastern equatorial Pacific, all datasets show consistency in their statistically significant trends, with warming everywhere except the far northwestern Atlantic; the largest warming trends are found in the middle latitudes of both hemispheres. Two of the SST reconstructions exhibit statistically significant cooling trends over the eastern equatorial Pacific, in disagreement with the un-interpolated SST and marine air temperature datasets which show statistically significant warming in this region. Twentieth century trends in tropical marine cloudiness, precipitation and SLP from independent data sets provide physically consistent evidence for a reduction in the strength of the atmospheric Walker Circulation accompanied by an eastward shift of deep convection from the western to the central equatorial Pacific. C. Deser A. S. Phillips M. A. Alexander 2014-07-15T22:10:41Z 2014-07-15T22:10:41Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1064 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1064 2014-07-15T22:10:41Z Projecting North American Climate over the Next 50 Years: Uncertainty due to Internal Variability This study highlights the relative importance of internally generated versus externally forced climate trends over the next 50 yr (2010–60) at local and regional scales over North America in two global coupled model ensembles. Both ensembles contain large numbers of integrations (17 and 40): each of which is subject to identical anthropogenic radiative forcing (e.g., greenhouse gas increase) but begins from a slightly different initial atmospheric state. Thus, the diversity of projected climate trends within each model ensemble is due solely to intrinsic, unpredictable variability of the climate system. Both model ensembles show that natural climate variability superimposed upon forced climate change will result in a range of possible future trends for surface air temperature and precipitation over the next 50 yr. Precipitation trends are particularly subject to uncertainty as a result of internal variability, with signal-to-noise ratios less than 2. Intrinsic atmospheric circulation variability is mainly responsible for the spread in future climate trends, imparting regional coherence to the internally driven air temperature and precipitation trends. The results underscore the importance of conducting a large number of climate change projections with a given model, as each realization will contain a different superposition of unforced and forced trends. Such initial-condition ensembles are also needed to determine the anthropogenic climate response at local and regional scales and provide a new perspective on how to usefully compare climate change projections across models. C. Deser A. S. Phillips M. A. Alexander B. V. Smoliak 2012-11-09T23:02:57Z 2013-05-06T16:10:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/602 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/602 2012-11-09T23:02:57Z ENSO and Pacific Decadal Variability in the Community Climate System Model Version 4 This study presents an overview of the El Niño–Southern Oscillation (ENSO) phenomenon and Pacific decadal variability (PDV) simulated in a multicentury preindustrial control integration of the NCAR Community Climate System Model version 4 (CCSM4) at nominal 1° latitude–longitude resolution. Several aspects of ENSO are improved in CCSM4 compared to its predecessor CCSM3, including the lengthened period (3–6 yr), the larger range of amplitude and frequency of events, and the longer duration of La Niña compared to El Niño. However, the overall magnitude of ENSO in CCSM4 is overestimated by ~30%. The simulated ENSO exhibits characteristics consistent with the delayed/recharge oscillator paradigm, including correspondence between the lengthened period and increased latitudinal width of the anomalous equatorial zonal wind stress. Global seasonal atmospheric teleconnections with accompanying impacts on precipitation and temperature are generally well simulated, although the wintertime deepening of the Aleutian low erroneously persists into spring. The vertical structure of the upper-ocean temperature response to ENSO in the north and south Pacific displays a realistic seasonal evolution, with notable asymmetries between warm and cold events. The model shows evidence of atmospheric circulation precursors over the North Pacific associated with the "seasonal footprinting mechanism," similar to observations. Simulated PDV exhibits a significant spectral peak around 15 yr, with generally realistic spatial pattern and magnitude. However, PDV linkages between the tropics and extratropics are weaker than observed. C. Deser A. S. Phillips R. A. Tomas Y. M. Okumura M. A. Alexander A. Capotondi J. D. Scott et al. 2016-04-21T21:01:32Z 2016-04-21T21:01:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1353 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1353 2016-04-21T21:01:32Z Does ocean coupling matter for the northern extratropical response to projected Arctic sea ice loss? The question of whether ocean coupling matters for the extratropical Northern Hemisphere atmospheric response to projected late 21st century Arctic sea ice loss is addressed using a series of experiments with Community Climate System Model version 4 at 1° spatial resolution under different configurations of the ocean model component: no interactive ocean, thermodynamic slab ocean, and full-depth (dynamic plus thermodynamic) ocean. Ocean-atmosphere coupling magnifies the response to Arctic sea ice loss but does not change its overall structure; however, a slab ocean is inadequate for inferring the role of oceanic feedbacks. The westerly winds along the poleward flank of the eddy-driven jet weaken in response to Arctic sea ice loss, accompanied by a smaller-magnitude strengthening on the equatorward side, with largest amplitudes in winter. Dynamical and thermodynamic oceanic feedbacks amplify this response by approximately 50%. Air temperature, precipitation, and sea level pressure responses also show sensitivity to the degree of ocean coupling. C. Deser L. Sun R. A. Tomas J. A. Screen 2012-09-26T16:25:59Z 2013-05-07T19:59:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/224 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/224 2012-09-26T16:25:59Z The Seasonal Atmospheric Response to Projected Arctic Sea Ice Loss in the Late Twenty-First Century The authors investigate the atmospheric response to projected Arctic sea ice loss at the end of the twenty-first century using an atmospheric general circulation model (GCM) coupled to a land surface model. The response was obtained from two 60-yr integrations: one with a repeating seasonal cycle of specified sea ice conditions for the late twentieth century (1980–99) and one with that of sea ice conditions for the late twenty-first century (2080–99). In both integrations, a repeating seasonal cycle of SSTs for 1980–99 was prescribed to isolate the impact of projected future sea ice loss. Note that greenhouse gas concentrations remained fixed at 1980–99 levels in both sets of experiments. The twentieth- and twenty-first-century sea ice (and SST) conditions were obtained from ensemble mean integrations of a coupled GCM under historical forcing and Special Report on Emissions Scenarios (SRES) A1B scenario forcing, respectively. The loss of Arctic sea ice is greatest in summer and fall, yet the response of the net surface energy budget over the Arctic Ocean is largest in winter. Air temperature and precipitation responses also maximize in winter, both over the Arctic Ocean and over the adjacent high-latitude continents. Snow depths increase over Siberia and northern Canada because of the enhanced winter precipitation. Atmospheric warming over the high-latitude continents is mainly confined to the boundary layer (below 850 hPa) and to regions with a strong low-level temperature inversion. Enhanced warm air advection by submonthly transient motions is the primary mechanism for the terrestrial warming. A significant large-scale atmospheric circulation response is found during winter, with a baroclinic (equivalent barotropic) vertical structure over the Arctic in November–December (January–March). This response resembles the negative phase of the North Atlantic Oscillation in February only. Comparison with the fully coupled model reveals that Arctic sea ice loss accounts for most of the seasonal, spatial, and vertical structure of the high-latitude warming response to greenhouse gas forcing at the end of the twenty-first century. C. Deser R. Tomas M. A. Alexander D. M. Lawrence 2012-10-15T23:24:16Z 2013-05-07T17:31:57Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/302 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/302 2012-10-15T23:24:16Z The transient atmospheric circulation response to North Atlantic SST and sea ice anomalies The objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of SST and sea ice extent anomalies in the North Atlantic sector using a large ensemble of experiments with the NCAR Community Climate Model version 3 (CCM3). The initial adjustment of the atmospheric circulation is characterized by an out-of-phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing. This initial baroclinic response reaches a maximum amplitude in 5–10 days, and persists for 2–3 weeks. Diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing. Following the initial baroclinic stage of adjustment, the response becomes progressively more barotropic and increases in both spatial extent and magnitude. The equilibrium stage of adjustment is reached in 2–2.5 months, and is characterized by an equivalent barotropic structure that resembles the hemispheric North Atlantic Oscillation–Northern Annular Mode (NAO–NAM) pattern, the model's leading internal mode of circulation variability over the Northern Hemisphere. The maximum amplitude of the equilibrium response is approximately 2–3 times larger than that of the initial response. The equilibrium response is primarily maintained by nonlinear transient eddy fluxes of vorticity (and, to a lesser extent, heat), with diabatic heating making a limited contribution in the vicinity of the forcing. C. Deser R. A. Tomas S. Peng 2012-11-13T18:04:46Z 2013-05-02T16:31:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/625 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/625 2012-11-13T18:04:46Z Atmospheric Rivers, Floods and the Water Resources of California California's highly variable climate and growing water demands combine to pose both water-supply and flood-hazard challenges to resource managers. Recently important efforts to more fully integrate the management of floods and water resources have begun, with the aim of benefitting both sectors. California is shown here to experience unusually large variations in annual precipitation and streamflow totals relative to the rest of the US, variations which mostly reflect the unusually small average number of wet days per year needed to accumulate most of its annual precipitation totals (ranging from 5 to 15 days in California). Thus whether just a few large storms arrive or fail to arrive in California can be the difference between a banner year and a drought. Furthermore California receives some of the largest 3-day storm totals in the country, rivaling in this regard the hurricane belt of the southeastern US. California's largest storms are generally fueled by landfalling atmospheric rivers (ARs). The fractions of precipitation and streamflow totals at stations across the US that are associated with ARs are documented here and, in California, contribute 20–50% of the state's precipitation and streamflow. Prospects for long-lead forecasts of these fractions are presented. From a meteorological perspective, California's water resources and floods are shown to derive from the same storms to an extent that makes integrated flood and water resources management all the more important. M. D. Dettinger F. M. Ralph T. Das P. J. Neiman D. R. Cayan 2012-06-29T14:28:15Z 2013-05-03T17:12:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/34 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/34 2012-06-29T14:28:15Z Design and quantification of an extreme winter storm scenario for emergency preparedness and planning exercises in California The USGS Multihazards Project is working with numerous agencies to evaluate and plan for hazards and damages that could be caused by extreme winter storms impacting California. Atmospheric and hydrological aspects of a hypothetical storm scenario have been quantified as a basis for estimation of human, infrastructure, economic, and environmental impacts for emergency-preparedness and flood-planning exercises. In order to ensure scientific defensibility and necessary levels of detail in the scenario description, selected historical storm episodes were concatentated to describe a rapid arrival of several major storms over the state, yielding precipitation totals and runoff rates beyond those occurring during the individual historical storms. This concatenation allowed the scenario designers to avoid arbitrary scalings and is based on historical occasions from the 19th and 20th Centuries when storms have stalled over the state and when extreme storms have arrived in rapid succession. Dynamically consistent, hourly precipitation, temperatures, barometric pressures (for consideration of storm surges and coastal erosion), and winds over California were developed for the so-called ARkStorm scenario by downscaling the concatenated global records of the historical storm sequences onto 6- and 2-km grids using a regional weather model of January 1969 and February 1986 storm conditions. The weather model outputs were then used to force a hydrologic model to simulate ARkStorm runoff, to better understand resulting flooding risks. Methods used to build this scenario can be applied to other emergency, nonemergency and non-California applications. M. D. Dettinger F. M. Ralph M. Hughes T. Das P. J. Neiman D. Cox G. Estes R. Reynolds R. Hartman D. Cayan L. Jones 2017-04-13T23:04:07Z 2017-04-13T23:04:07Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1488 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1488 2017-04-13T23:04:07Z Drought risk assessment under climate change is sensitive to methodological choices for the estimation of evaporative demand Several studies have projected increases in drought severity, extent and duration in many parts of the world under climate change. We examine sources of uncertainty arising from the methodological choices for the assessment of future drought risk in the continental US (CONUS). One such uncertainty is in the climate models' expression of evaporative demand (E0), which is not a direct climate model output but has been traditionally estimated using several different formulations. Here we analyze daily output from two CMIP5 GCMs to evaluate how differences in E0 formulation, treatment of meteorological driving data, choice of GCM, and standardization of time series influence the estimation of E0. These methodological choices yield different assessments of spatio-temporal variability in E0 and different trends in 21st century drought risk. First, we estimate E0 using three widely used E0 formulations: Penman-Monteith; Hargreaves-Samani; and Priestley-Taylor. Our analysis, which primarily focuses on the May-September warm-season period, shows that E0 climatology and its spatial pattern differ substantially between these three formulations. Overall, we find higher magnitudes of E0 and its interannual variability using Penman-Monteith, in particular for regions like the Great Plains and southwestern US where E0 is strongly influenced by variations in wind and relative humidity. When examining projected changes in E0 during the 21st century, there are also large differences among the three formulations, particularly the Penman-Monteith relative to the other two formulations. The 21st century E0 trends, particularly in percent change and standardized anomalies of E0, are found to be sensitive to the long-term mean value and the amplitude of interannual variability, i.e. if the magnitude of E0 and its interannual variability are relatively low for a particular E0 formulation, then the normalized or standardized 21st century trend based on that formulation is amplified relative to other formulations. This is the case for the use of Hargreaves-Samani and Priestley-Taylor, where future E0 trends are comparatively much larger than for Penman-Monteith. When comparing Penman-Monteith E0 responses between different choices of input variables related to wind speed, surface roughness, and net radiation, we found differences in E0 trends, although these choices had a much smaller influence on E0 trends than did the E0 formulation choices. These methodological choices and specific climate model selection, also have a large influence on the estimation of trends in standardized drought indices used for drought assessment operationally. We find that standardization tends to amplify divergences between the E0 trends calculated using different E0 formulations, because standardization is sensitive to both the climatology and amplitude of interannual variability of E0. For different methodological choices and GCM output considered in estimating E0, we examine potential sources of uncertainty in 21st century trends in the Standardized Precipitation Evapotranspiration Index (SPEI) and Evaporative Demand Drought Index (EDDI) over selected regions of the CONUS to demonstrate the practical implications of these methodological choices for the quantification of drought risk under climate change. C. Dewes I. Rangwala J. J. Barsugli M. T. Hobbins S. Kumar 2012-11-15T18:20:22Z 2013-05-07T23:24:45Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/775 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/775 2012-11-15T18:20:22Z Central Pacific El Niño and decadal climate change in the North Pacific Ocean Decadal fluctuations of the ocean and atmosphere over the North Pacific Ocean significantly affect the weather and climate of North America and Eurasia. They also cause transitions between different states of marine ecosystems across the Pacific Ocean1, 2, 3. An important fraction of North Pacific low-frequency variability is linked to the North Pacific Gyre Oscillation4, a climate pattern associated with decadal fluctuations of the ocean circulation. Decadal variations in the North Pacific Gyre Oscillation are characterized by a pattern of sea surface temperature anomalies that resemble the central Pacific El Niño, a dominant mode of interannual variability with far-reaching effects on global climate patterns5, 6, 7. Here we use an ensemble of simulations with a coupled ocean–atmosphere model to show that the sea surface temperature anomalies associated with central Pacific El Niño force changes in the extra-tropical atmospheric circulation. These changes in turn drive the decadal fluctuations of the North Pacific Gyre Oscillation. Given that central Pacific El Niño events could become more frequent with increasing levels of greenhouse gases in the atmosphere8, we infer that the North Pacific Gyre Oscillation may play an increasingly important role in shaping Pacific climate and marine ecosystems in the twenty-first century. E. Di Lorenzo K. M. Cobb J. C. Furtado N. Schneider B. T. Anderson A. Bracco M. A. Alexander D. J. Vimont 2016-04-11T21:35:31Z 2016-04-11T21:35:31Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1321 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1321 2016-04-11T21:35:31Z ENSO and meridional modes: A null hypothesis for Pacific climate variability Pacific low-frequency variability (timescale > 8 years) exhibits a well-known El Niño-like pattern of basin-scale sea surface temperature, which is found in all the major modes of Pacific decadal climate. Using a set of climate model experiments and observations, we decompose the mechanisms contributing to the growth, peak, and decay of the Pacific low-frequency spatial variance. We find that the El Niño-like interdecadal pattern is established through the combined actions of Pacific meridional modes (MM) and the El Niño–Southern Oscillation (ENSO). Specifically, in the growth phase of the pattern, subtropical stochastic excitation of the MM energizes the tropical low-frequency variance acting as a red noise process. Once in the tropics, this low-frequency variance is amplified by ocean-atmospheric feedbacks as the pattern reaches its peak phase. At the same time, atmospheric teleconnections distribute the variance from the tropics to the extratropics, where the pattern ultimately decays. In this stochastic red noise model of Pacific climate, the timescale of the extra-tropical/tropical interactions (1–2 years) permits the stochastic excitation of the ENSO-like pattern of decadal and interdecadal variance. E. Di Lorenzo G. Liguori N. Schneider J. C. Furtado B. T. Anderson M. A. Alexander 2012-11-13T21:09:40Z 2013-05-08T15:39:38Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/652 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/652 2012-11-13T21:09:40Z Constructing Retrospective Gridded Daily Precipitation and Temperature Datasets for the Conterminous United States This paper presents and evaluates a method for the construction of long-range and wide-area temporal spatial datasets of daily precipitation and temperature (maximum and minimum). This method combines the interpolation of daily ratios/fractions derived from ground-based meteorological station records and respective fields of monthly estimates. Data sources for the described implementation over the conterminous United States (CONUS) are two independent and quality-controlled inputs: 1) an enhanced compilation of daily observations derived from the National Climatic Data Center digital archives and 2) the Parameter–Elevation Regressions on Independent Slopes Model (PRISM) maps. The results of this study show that this nonconventional interpolation preserves the spatial and temporal distribution of both the PRISM maps (monthly, topography-sensitive patterns) and the original daily observations. Statistics of a preliminary point comparison with the observed values at high-quality and independent reference sites show a reasonable agreement and a noticeable improvement over the nearest station method in orographically sensitive areas. The implemented datasets provide daily precipitation and temperature values at 2.5-min (around 4 km) resolution for 1960–2001. Combining seamless spatial and temporal coverage and topographic sensitivity characteristics, the datasets offer the potential for supporting current and future regional and historical hydrologic assessments over the CONUS. M. Di Luzio G. L. Johnson C. Daly J. K. Eischeid et al. 2015-04-27T15:58:05Z 2015-10-07T15:50:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1162 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1162 2015-04-27T15:58:05Z Influence of the basic state zonal flow on convectively coupled equatorial waves. Observational data are used to test the hypothesis that the basic state modulates the dispersion properties of convectively coupled equatorial waves (CCEWs). This hypothesis is based on shallow water theory, which predicts that the zonal speed of propagation of such tropospheric equatorial modes is altered by the equivalent depth and the basic zonal flow. Localized space-time spectra are calculated to investigate how CCEW spectral peaks vary across the tropics and how they are affected by the variations in zonal wind observed geographically and by season. Doppler shifting by the basic state barotropic zonal flow is readily identified. Once this Doppler shifting is taken into account, the equivalent depths of CCEWs inferred from global power spectra are surprisingly uniform, both geographically and temporally. However, there are also detectable modulations that appear consistent with changes in vertical shear of the zonal flow, along with other shifts that are not as easily explained. J. Dias G. N. Kiladis 2016-07-08T16:31:35Z 2016-07-08T16:32:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1367 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1367 2016-07-08T16:31:35Z The Relationship between Equatorial Mixed Rossby–Gravity and Eastward Inertio-Gravity Waves. Part II Space–time spectral analysis of tropical cloudiness data shows strong evidence that convectively coupled n = 0 mixed Rossby–gravity waves (MRGs) and eastward inertio-gravity waves (EIGs) occur primarily within the western/central Pacific Ocean. Spectral filtering also shows that MRG and EIG cloudiness patterns are antisymmetric with respect to the equator, and they propagate coherently toward the west and east, respectively, with periods between 3 and 5 days, in agreement with Matsuno's linear shallow-water theory. In contrast to the spectral approach, in a companion paper it has been shown that empirical orthogonal functions (EOFs) of 2–6-day-filtered cloudiness data within the tropical Pacific Ocean also suggest an antisymmetric pattern, but with the leading EOFs implying a zonally standing but poleward-propagating oscillation, along with the associated tropospheric flow moving to the west. In the present paper, these two views are reconciled by applying an independent approach based on a tracking method to assess tropical convection organization. It is shown that, on average, two-thirds of MRG and EIG events develop independently of one another, and one-third of the events overlap in space and time. This analysis also verifies that MRG and EIG cloudiness fields tend to propagate meridionally away from the equator. It is demonstrated that the lack of zonal propagation implied from the EOF analysis is likely due to the interference between eastward- and westward-propagating disturbances. In addition, it is shown that the westward-propagating circulation associated with the leading EOF is consistent with the expected theoretical behavior of an interference between MRGs and EIGs. J. Dias G. N. Kiladis 2013-08-26T22:15:15Z 2013-08-26T22:15:15Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/947 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/947 2013-08-26T22:15:15Z How systematic is organized tropical convection within the MJO? Recent theories of the dynamics of the Madden-Julian Oscillation (MJO) have been building on its multiscale structure. While it is observed that much of the convection within the MJO envelope is related to higher frequency equatorial waves, it is not known to what extent this organization is systematic from one MJO event to another. For instance, it is of interest to know whether MJO favors waves of particular types and propagation direction, and how this variability changes seasonally. This work presents a wavenumber-frequency spectral analysis of the MJO convective envelope, which indicates that there is no strong preferred scale of high frequency organization that is ubiquitous to the MJO. This null finding supports the use of convective parametrizations in modeling the MJO since, while moist convection is likely critical to its initiation and maintenance, the particular details of that organization may not be critical for its prediction and simulation. J. Dias S. Leroux S. N. Tulich G. N. Kiladis 2014-01-09T01:21:29Z 2014-01-09T01:21:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1013 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1013 2014-01-09T01:21:29Z Modulation of Shallow-Water Equatorial Waves due to a Varying Equivalent Height Background The dynamics of convectively coupled equatorial waves (CCEWs) is analyzed in an idealized model of the large-scale atmospheric circulation. The model is composed of a linear rotating shallow-water system with a variable equivalent height, or equivalent gravity wave speed, which varies in space. This model is based on the hypothesis that moist convection acts to remove convective instability, therefore modulating the equivalent height of a shallow-water system. Asymptotic solutions are derived in the case of a small perturbation around a constant coefficient, which is assumed to be a mean moist equivalent height derived from satellite observations. The first-order solutions correspond to the free normal modes of the linear shallow-water system and the second-order flow is derived solving a perturbation eigenvalue problem. The asymptotic solutions are documented in the case of a zonally varying equivalent height and for wavenumbers and frequencies that are consistent with observations of CCEWs. This analysis shows that the dynamics of the secondary divergence and its impact on the full divergence varies mode by mode. For instance, for a negative equivalent height anomaly, which is interpreted as a moister background, the secondary divergence is nearly in phase with the primary divergence in the case of Kelvin waves—in contrast to mixed Rossby–gravity waves where the secondary divergence acts to attenuate the primary divergence. While highly idealized, the modeled waves share some features with observations, providing a mechanism for the relationship between CCEWs phase speed, amplitude, and horizontal structure. J. Dias P. L. Silva Dias G. N. Kiladis M. Gehne 2012-12-21T21:08:32Z 2013-05-03T23:08:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/850 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/850 2012-12-21T21:08:32Z An Object-Based Approach to Assessing the Organization of Tropical Convection The organization of tropical convection is assessed through an object-based analysis of satellite brightness temperature data Tb, a proxy for convective activity. The analysis involves the detection of contiguous cloud regions (CCRs) in the three-dimensional space of latitude, longitude, and time where Tb falls below a given threshold. A range of thresholds is considered and only CCRs that satisfy a minimum size constraint are retained in the analysis. Various statistical properties of CCRs are documented including their zonal speed of propagation, which is estimated using a Radon transformation technique. Consistent with previous studies, a majority of CCRs are found to propagate westward, typically at speeds of around 15 m s−1, regardless of underlying Tb threshold. Most of these zonally propagating CCRs have lifetimes less than 2 days and zonal widths less than 800 km, implying aggregation of just a few individual mesoscale convective systems. This object-based perspective is somewhat different than that obtained in previous Fourier-based analyses, which primarily emphasize the organization of convection on synoptic and planetary scales via wave–convection coupling. To reconcile these contrasting views, an object-based data reconstruction is developed that objectively demonstrates how the spectral peaks of synoptic- to planetary-scale waves can be attributed to the organization of CCRs into larger-scale wave envelopes. A novel method based on the randomization of CCRs in physical space leads to an empirical background spectrum for organized tropical convection that does not rely on any smoothing in spectral space. Normalization by this background reveals spectral peaks associated with synoptic- and planetary-scale waves that are consistent with previous studies. J. Dias S. N. Tulich G. N. Kiladis 2013-08-28T17:24:54Z 2013-08-28T17:24:54Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/975 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/975 2013-08-28T17:24:54Z Climate in medieval time: How anomalous? N/A H. F. Diaz 2012-06-29T14:30:53Z 2013-05-02T16:11:33Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/35 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/35 2012-06-29T14:30:53Z Climate in medieval times: How anomalous? N/A H. F. Diaz 2015-04-27T16:08:04Z 2015-10-07T16:04:42Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1163 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1163 2015-04-27T16:08:04Z Climatic changes in mountain regions of the American Cordillera and the Tropics: Historical changes and future outlook. We review some recent work regarding climatic changes in selected mountain regions, with particular attention to the tropics and the American Cordillera. Key aspects of climatic variability and trends in these regions are the amplification of surface warming trends with height, and the strong modulation of tempera- ture trends by tropical sea surface temperature, largely controlled by changes in El Niño–Southern Oscillation on multiple time scales. Corollary aspects of these climate trends include the increase in a critical plant growth temperature threshold, a rise in the freezing level surface, and the possibility of enhanced subtropical drying. Anthropogenic global warming projections indicate a strong likelihood for enhancement of these observed changes. H. F. Diaz R. S. Bradley L. Ning 2012-10-15T23:46:02Z 2013-05-07T17:31:33Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/305 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/305 2012-10-15T23:46:02Z Disappearing "Alpine Tundra" Köppen climatic type in the western United States We examine changes in the areal extent of the Köppen "alpine tundra" climate classification type for the mountainous western United States following the work of Kottek et al. (2006). We find a significant decline in the area occupied by this climate category. In the early decades of the 20th century, the mean temperature of the warmest month in the areas of the western U.S. with nominal alpine tundra climates ranged largely between ∼8.5°C and 9.5°C. In the last 20 years (1987–2006), rising temperatures have caused a significant fraction of these areas to exceed the 10°C threshold for alpine tundra classification. The result has been a 73% reduction in coverage of this climatic type. The remaining classified alpine tundra in the last 20 years now averages between ∼9°C–10°C during the warmest month, so that continued warming past the classification threshold, would imply that areas where this climate type is found today in the West will no longer be present. H. F. Diaz J. K. Eischeid 2012-12-21T21:13:14Z 2013-04-24T17:39:32Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/851 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/851 2012-12-21T21:13:14Z Changes in atmospheric circulation patterns associated with high and low rainfall regimes in the Hawaiian Islands region on multiple time scales We examine a suite of climate variables in the North Pacific associated with different temporal scales of dry and wet episodes in the Hawaiian Islands. The goal is to ascertain whether varying the length in the occurrence of such events from seasonal to multi-decadal results from different ocean–atmosphere circulation patterns over the North Pacific region. We find that as the dryness period lengthens, the spatial scale of the anomalies widens, but the characteristics of the anomalous circulation fields exhibit elements evident at each time scale. At the longest (multi-decadal) time scales during the wet season (November–April), the major anomalous circulation features associated with above (below) average rainfall in Hawai'i are a strengthening (weakening) of the North Pacific mid-latitude westerlies associated with a strengthened (weakened) Aleutian Low system, a slight weakening (strengthening) of the northeast trade winds, with anomalous northerly (southerly) component to the south of the Islands, together with diminished (enhanced) precipitation across most of the tropical North Pacific. During the summer dry season (May–October) a characteristic pattern that is evident at different time scales during drier than normal periods is a strengthening of the trade winds to the south of the Islands, with sinking motion extending from the latitude of Hawai'i eastward to Central America. Conversely, wet summers are associated with generally weaker trades to the south with a tendency for anomalous southwesterly component. We also consider possible changes in the relationship of Hawaiian rainfall to changes in the Pacific-Decadal Oscillation (PDO) but conclude that the record is too short to establish the significance of any changes in an overall negative correlation. H. F. Diaz T. W. Giambelluca 2012-11-13T18:10:36Z 2013-05-02T16:32:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/626 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/626 2012-11-13T18:10:36Z Changes in the vertical profiles of mean temperature and humidity in the Hawaiian Islands Recent drought and warmer than normal temperatures affecting the Hawaiian Islands have raised concern among natural resource managers that impacts associated with global warming are becoming manifest in the region. A number of studies published over the past few decades have documented changes in the climate of Hawai'i that are generally consistent with expectations from climate change projections, such as those found in the latest Intergovernmental Panel on Climate Change assessment report (IPCC, 2007). In this study we examine a suite of climate variables that are important from the point of view of ecosystem impacts, but that also relate to societal concerns such Island water resources. Our results are consistent with previous studies in showing a significant warming trend, especially evident at higher elevations. In particular, we document a decrease in the frequency of occurrence of freezing temperatures in the upper slopes of the higher terrain on Maui and the Big Island and a concomitant rise in the freezing level surface in the region that is in good agreement with analogous studies done for other mountainous areas of the world. Temperatures at standard reference surfaces in the free atmosphere have warmed throughout the troposphere, with a maximum near the 850 mb level. The warming peak at this level could be associated with an increased frequency of occurrence and/or lowering of the trade wind inversion layer. H. F. Diaz T. W. Giambelluca J. K. Eischeid 2012-11-13T21:03:54Z 2013-05-08T15:39:12Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/651 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/651 2012-11-13T21:03:54Z The significance of weather and climate extremes to society: an introduction N/A H. F. Diaz R. J. Murnane 2014-01-09T01:30:05Z 2014-01-09T01:30:05Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1014 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1014 2014-01-09T01:30:05Z The Wildfires of 1910: Climatology of an Extreme Early Twentieth-Century Event and Comparison with More Recent Extremes During the summer of 1910 large wildfires occurred throughout the western United States, and especially in the northern Rocky Mountains. The "Great Idaho Fires" of 1910 alone burned about three million acres (~1.2 Mha)— an area that is approximately the size of Connecticut. Multiple fires ignited and coalesced, burning in forests of northern Idaho and western Montana including parts of the Bitterroot, Cabinet, Clearwater, Coeur d'Alene, Flathead, Kaniksu, Kootenai, Lewis and Clark, Lolo, and St. Joe National Forests. The firestorm burned for days in late August of 1910 and killed 87 people, including 78 firefighters. It is believed to be the largest, although not the deadliest, wildfire complex in recorded U.S. history. Here we show that highly anomalous weather preceded the conflagration in much of the West, including the occurrence of the warmest March on record for the contiguous United States (except March 2012). While the occurrence of very high winds greatly contributed to the fast spread of the wildfire, the preceding highly anomalous warm and dry condition since the spring of 1910 likely also contributed to the magnitude of this event. Improved understanding of extreme wildfire outbreaks and climatological conditions associated with them is increasingly important, as such events are increasing in frequency as global and regional warming continues. H. F. Diaz T. W. Swetnam 2012-06-29T14:32:44Z 2013-05-02T16:12:11Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/36 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/36 2012-06-29T14:32:44Z Spatial and temporal characteristics of climate in medieval times revisited Developing accurate reconstructions of past climate regimes and enhancing our understanding of the causal factors that may have contributed to their occurrence is important for a number of reasons; these include improvements in the attribution of climate change to natural and anthropogenic forcing, gaining a better appreciation for the range and magnitude of low-frequency variability and previous climatic regimes in comparison with the modern instrumental period, and developing greater insights into the relationship between human society and climatic changes. This paper examine upto- date evidence regarding the characteristics of the climate in medieval times (A.D. ~950–1400). Long and high-resolution climate proxy records reported in the scientific literature, which form the basis for the climate reconstructions, have greatly expanded in the last few decades, with greater numbers of sites that now cover more areas of the globe. Some comparisons with the modern climate record and discussion of potential mechanisms associated with the patterns of medieval climate are presented here, but our main goal is to provide the reader with some appreciation of the richness of past natural climate variability in terms of its spatial and temporal characteristics. H. F. Diaz R. Trigo M. K. Hughes M. E. Mann E. Xoplaki D. Barriopedro 2014-07-15T22:13:22Z 2014-07-15T22:13:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1065 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1065 2014-07-15T22:13:22Z Some Perspectives on Societal Impacts of Past Climatic Changes We examine a range of paleoclimatic evidence covering approximately the last 2000 years (the Common Era) to provide plausible environmental scenarios as potential drivers and stressors associated with major societal disruption in different parts of the world. The period studied covers both historical, for which there is documentary evidence of impacts, and prehistorical events, for which impacts are inferred from the archeological record. Drought appears to be the most common high-impact stressor in the historical and prehistorical records. Clearly, the adequacy of water supplies for growing food and for an array of other uses is a thread that weaves its way across time and societies. We also briefly outline some of the key physical mechanisms leading to climatic changes of a magnitude that could have led to societal disruptions. These include solar variability and large explosive volcanic eruptions, both of which affect the amount of radiant energy available to the Earth's climate system, as well as the natural internal variability of the climate system. We emphasize that climatic changes alone are unlikely to be the sole determinant cause of a given society's response – whether abandonment of settlements or bellicose action against its own members or neighbors. Often, the natural hazard is simply a catalyst for actions whose groundwork had been set in motion for some time prior. In many cases, appropriate mitigation to reduce vulnerability and efforts to enhance a society's adaptive capacity might have been enough to prevent the most extreme consequences of the nature's extremes. In that vein, we point to current conditions in the western United States, where a complex mix of past and current actions together with a rapidly changing climate are causing a plethora of problems whose solution will demand creative collaborative actions at all levels of society. H. F. Diaz V. Trouet 2012-09-23T02:27:01Z 2013-05-10T20:20:52Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/118 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/118 2012-09-23T02:27:01Z The impact of climate change in the American Cordillera The mountain regions comprising the western American Cordillera (from Alaska to southern Argentina and Chile) are especially vulnerable to changes in climate and to the ensuing changes in snowpack, streamflow, ecosystem functioning, and a host of other impacts on human and nonhuman systems. The effect of elevation on temperature and precipitation induces a compression of the typical meridional climatic gradients, causing changes in life zones—geographic regions or areas defined by their characteristic life forms, e.g., alpine, sub-alpine, coniferous forests, and so forth—over relatively short distances. In mountain regions, relatively small perturbations in global processes can operate through the system to produce large local changes. Because mountains provide life-sustaining water for people living there as well as in adjacent lowland regions, climatic and other environmental changes in the American Cordillera will have a large impact on the future well-being of an area far larger than the mountain region itself. H. F. Diaz R. Villalba G. Greenwood R. S. Bradley 2015-10-07T16:06:09Z 2015-10-07T16:06:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1232 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1232 2015-10-07T16:06:09Z Recent California Water Year Precipitation Deficits: A 440-Year Perspective An analysis of the October 2013–September 2014 precipitation in the western United States and in particular over the California–Nevada region suggests this anomalously dry season, while extreme, is not unprecedented in comparison with the approximately 120-yr-long instrumental record of water year (WY; October–September) totals and in comparison with a 407-yr WY precipitation reconstruction dating back to 1571. Over this longer period, nine other years are known or estimated to have been nearly as dry or drier than WY 2014. The 3-yr deficit for WYs 2012–14, which in California exceeded the annual mean precipitation, is more extreme but also not unprecedented, occurring three other times over the past approximate 440 years in the reconstruction. WY precipitation has also been deficient on average for the past 14 years, and such a run of predominantly dry WYs is also a rare occurrence in the authors' merged reconstructed plus instrumental period record. H. F. Diaz E. R. Wahl 2016-10-14T14:56:45Z 2016-10-14T14:56:45Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1403 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1403 2016-10-14T14:56:45Z A Five-Century Reconstruction of Hawaiian Islands Winter Rainfall Few if any high-resolution (annually resolved) paleoclimate records are available for the Hawaiian Islands prior to ~1850 CE, after which some instrumental records start to become available. This paper shows how atmospheric teleconnection patterns between North America and the northeastern North Pacific (NNP) allow for reconstruction of Hawaiian Islands rainfall using remote proxy information from North America. Based on a newly available precipitation dataset for the state of Hawaii and observed and reconstructed December–February (DJF) sea level pressures (SLPs) in the North Pacific Ocean, the authors make use of a strong relationship between winter SLP variability in the northeast Pacific and corresponding DJF Hawaii rainfall variations to reconstruct and evaluate that season's rainfall over the period 1500–2012 CE. A general drying trend, though with substantial decadal and longer-term variability, is evident, particularly during the last ~160 years. Hawaiian Islands rainfall exhibits strong modulation by El Niño–Southern Oscillation (ENSO), as well as in relation to Pacific decadal oscillation (PDO)-like variability. For significant periods of time, the reconstructed large-scale changes in the North Pacific SLP field described here and by construction the long-term decline in Hawaiian winter rainfall are broadly consistent with long-term changes in tropical Pacific sea surface temperature (SST) based on ENSO reconstructions documented in several other studies, particularly over the last two centuries. Also noted are some rather large multidecadal fluctuations in rainfall (and hence in NNP SLP) in the eighteenth century of undetermined provenance. H. F. Diaz E. R. Wahl E. Zorita T. W. Giambelluca J. K. Eischeid 2012-10-15T23:45:49Z 2013-05-07T17:31:44Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/303 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/303 2012-10-15T23:45:49Z Climate and Cultural History in the Americas: An Overview There is abundant historical evidence that climatic extremes in the past have led to significant and sometimes severe societal impacts. The severity of these impacts depends on the intensity and duration of the climatic event, social organization, and the prevailing socioeconomic conditions at the time of the climatic extreme. In this issue of Climatic Change we present the results from 12 studies, which document climatic extremes on different time scales and provide interesting evidence for direct and indirect social impacts of climatic changes in the Americas during the pre-Hispanic, colonial, and modern eras. H. F. Diaz D. W. Stahle 2016-04-12T15:53:47Z 2016-04-12T15:53:47Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1351 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1351 2016-04-12T15:53:47Z Corrigendum to: PM2.5 analog forecast and Kalman filter post-processing for the Community Multiscale Air Quality (CMAQ) model A new post-processing method for surface particulate matter (PM2.5) predictions from the National Oceanic and Atmospheric Administration (NOAA) developmental air quality forecasting system using the Community Multiscale Air Quality (CMAQ) model is described. It includes three main components: • A real-time quality control procedure for surface PM2.5 observations; • Model post-processing at each observational site using historical forecast analogs and Kalman filtering; • Spreading the forecast corrections from the observation locations to the entire gridded domain. The methodology is tested using 12 months of CMAQ forecasts of hourly PM2.5, from December 01, 2009 through November 30, 2010. The model domain covers the contiguous USA, and model data are verified against U.S. Environmental Prediction Agency AIRNow PM2.5 observations measured at 716 stations over the CMAQ domain. The model bias is found to have a strong seasonal dependency, with a large positive bias in winter and a small bias in the summer months, and also to have a strong diurnal cycle. Five different post-processing techniques are compared, including a seven-day running mean subtraction, Kalman-filtering, analogs, and combinations of analogs and Kalman filtering. The most accurate PM2.5 forecasts have been found to be produced when applying the Kalman filter correction to the analog ensemble weighted mean, referred to as KFAN. The choice of analog predictors used in the analog search is also found to have a significant effect. A monthly error analysis is computed, in each case using the remaining 11 months of the data set for the analog searches. The improvement of KFAN errors over the raw CMAQ model errors ranges from 44 to 52% for MAE and 13–30% for the correlation coefficient. Since the post-processing analysis is only done at the locations where observations are available, the spreading of post-processing correction information over nearby model grid points is necessary to make forecast contour maps. This spreading of information is accomplished with an eight-pass Barnes-type iterative objective analysis scheme. The final corrected CMAQ forecast over the entire domain is composed of the sum of the original CMAQ forecasts and the KFAN bias information interpolated over the entire domain, and is applied on an hourly basis. I. Djalalova L. D. Monache J. M. Wilczak 2015-10-07T16:09:55Z 2015-10-07T16:09:55Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1233 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1233 2015-10-07T16:09:55Z PM2.5 analog forecast and Kalman filter post-processing for the Community Multiscale Air Quality (CMAQ) model A new post-processing method for surface particulate matter (PM2.5) predictions from the National Oceanic and Atmospheric Administration (NOAA) developmental air quality forecasting system using the Community Multiscale Air Quality (CMAQ) model is described. It includes three main components: • A real-time quality control procedure for surface PM2.5 observations; • Model post-processing at each observational site using historical forecast analogs and Kalman filtering; • Spreading the forecast corrections from the observation locations to the entire gridded domain. The methodology is tested using 12 months of CMAQ forecasts of hourly PM2.5, from December 01, 2009 through November 30, 2010. The model domain covers the contiguous USA, and model data are verified against U.S. Environmental Prediction Agency AIRNow PM2.5 observations measured at 716 stations over the CMAQ domain. The model bias is found to have a strong seasonal dependency, with a large positive bias in winter and a small bias in the summer months, and also to have a strong diurnal cycle. Five different post-processing techniques are compared, including a seven-day running mean subtraction, Kalman-filtering, analogs, and combinations of analogs and Kalman filtering. The most accurate PM2.5 forecasts have been found to be produced when using historical analogs of the hourly Kalman-filtered forecasts, referred to as KFAN. The choice of meteorological variables used in the hourly analog search is also found to have a significant effect. A monthly error analysis is computed, in each case using the remaining 11 months of the data set for the analog searches. The improvement of KFAN errors over the raw CMAQ model errors ranges from 50 to 75% for MAE and from 40 to 60% for the correlation coefficient. Since the post-processing analysis is only done at the locations where observations are available, the spreading of post-processing correction information over nearby model grid points is necessary to make forecast contour maps. This spreading of information is accomplished with an eight-pass Barnes-type iterative objective analysis scheme. The final corrected CMAQ forecast over the entire domain is composed of the sum of the original CMAQ forecasts and the KFAN bias information interpolated over the entire domain, and is applied on an hourly basis. I. Djalalova L. D. Monache J. M. Wilczak 2016-10-14T14:53:59Z 2016-10-14T14:53:59Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1402 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1402 2016-10-14T14:53:59Z The POWER Experiment: Impact of Assimilation of a Network of Coastal Wind Profiling Radars on Simulating Offshore Winds in and above the Wind Turbine Layer During the summer of 2004 a network of 11 wind profiling radars (WPRs) was deployed in New England as part of the New England Air Quality Study (NEAQS). Observations from this dataset are used to determine their impact on numerical weather prediction (NWP) model skill at simulating coastal and offshore winds through data-denial experiments. This study is a part of the Position of Offshore Wind Energy Resources (POWER) experiment, a Department of Energy (DOE) sponsored project that uses National Oceanic and Atmospheric Administration (NOAA) models for two 1-week periods to measure the impact of the assimilation of observations from 11 inland WPRs. Model simulations with and without assimilation of the WPR data are compared at the locations of the inland WPRs, as well as against observations from an additional WPR and a high-resolution Doppler lidar (HRDL) located on board the Research Vessel Ronald H. Brown (RHB), which cruised the Gulf of Maine during the NEAQS experiment. Model evaluation in the lowest 2 km above the ground shows a positive impact of the WPR data assimilation from the initialization time through the next five to six forecast hours at the WPR locations for 12 of 15 days analyzed, when offshore winds prevailed. A smaller positive impact at the RHB ship track was also confirmed. For the remaining three days, during which time there was a cyclone event with strong onshore wind flow, the assimilation of additional observations had a negative impact on model skill. Explanations for the negative impact are offered. I. Djalalova J. Olson J. R. Carley L. Bianco J. M. Wilczak Y. Pichugina R. M. Banta M. Marquis J. Cline 2012-09-26T16:33:22Z 2013-05-08T14:54:36Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/225 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/225 2012-09-26T16:33:22Z Ensemble and bias-correction technoqies for air quality model forecasts of Surface O3 and PM2.5 during the TEXAQS-II experiment of 2006 Several air quality forecasting ensembles were created from seven models, running in real-time during the 2006 Texas Air Quality (TEXAQS-II) experiment. These multi-model ensembles incorporated a diverse set of meteorological models, chemical mechanisms, and emission inventories. Evaluation of individual model and ensemble forecasts of surface ozone and particulate matter (PM) was performed using data from 119 EPA AIRNow ozone sites and 38 PM sites during a 50-day period in August and September of 2006. From the original set of models, two new bias-corrected model data sets were built, either by applying a simple running mean average to the past 7 days of data or by a Kalman-Filter approach. From the original and two bias-corrected data sets, three ensembles were created by a simple averaging of the seven models. For further improvements three additional weighted model ensembles were created, where individual model weights were calculated using the singular value decomposition method. All six of the ensembles are compared to the individual models and to each other in terms of root mean square error, correlation, and contingency and probabilistic statistics. In most cases, each of the ensembles show improved skill compared to the best of the individual models. The over all best ensemble technique was found to be the combination of Kalman-Filtering and weighted averaging. PM2.5 aerosol ensembles demonstrated significant improvement gains, mostly because the original model's skill was very low. I. Djalalova J. M. Wilczak S. A. McKeen G. A. Grell S. Peckman M. Pagowski L. DelleMonache J. T. McQueen Y. Tang P. Lee J. McHenry W. Gong V. Bouchet R. Mathur 2014-07-22T20:36:00Z 2014-07-22T20:36:00Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1066 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1066 2014-07-22T20:36:00Z The Making of an Extreme Event: Putting the Pieces Together We examine how physical factors spanning climate and weather contributed to record warmth over the central and eastern United States in March 2012, when daily temperature anomalies at many locations exceeded 20°C. Over this region, approximately 1°C warming in March temperatures has occurred since 1901. This long-term regional warming is an order of magnitude smaller than temperature anomalies observed during the event, indicating that most of the extreme warmth must be explained by other factors. Several lines of evidence strongly implicate natural variations as the primary cause for the extreme event. The 2012 temperature anomalies had a close analog in an exceptionally warm U.S. March occurring over 100 years earlier, providing observational evidence that an extreme event similar to March 2012 could be produced through natural variability alone. Coupled model forecasts and simulations forced by observed sea surface temperatures (SSTs) show that forcing from anomalous SSTs increased the probability of extreme warm temperatures in March 2012 above that anticipated from the long-term warming trend. In addition, forcing associated with a strong Madden–Julian oscillation further increased the probability for extreme U.S. warmth and provided important additional predictive information on the timing and spatial pattern of temperature anomalies. The results indicate that the superposition of a strong natural variation similar to March 1910 on longterm warming of the magnitude observed would be sufficient to account for the record warm March 2012 U.S. temperatures. We conclude that the extreme warmth over the central and eastern United States in March 2012 resulted primarily from natural climate and weather variability— a substantial fraction of which was predictable. R. M. Dole M. P. Hoerling A. Kumar J. K. Eischeid J. Perlwitz X.-W. Quan G. N. Kiladis R. S. Webb D. Murray M. Chen K. Wolter T. Zhang 2012-11-15T18:23:01Z 2013-05-06T17:02:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/776 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/776 2012-11-15T18:23:01Z Was there a basis for anticipating the 2010 Russian heat wave? The 2010 summer heat wave in western Russia was extraordinary, with the region experiencing the warmest July since at least 1880 and numerous locations setting all-time maximum temperature records. This study explores whether early warning could have been provided through knowledge of natural and human-caused climate forcings. Model simulations and observational data are used to determine the impact of observed sea surface temperatures (SSTs), sea ice conditions and greenhouse gas concentrations. Analysis of forced model simulations indicates that neither human influences nor other slowly evolving ocean boundary conditions contributed substantially to the magnitude of this heat wave. They also provide evidence that such an intense event could be produced through natural variability alone. Analysis of observations indicate that this heat wave was mainly due to internal atmospheric dynamical processes that produced and maintained a strong and long-lived blocking event, and that similar atmospheric patterns have occurred with prior heat waves in this region. We conclude that the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability. Slowly varying boundary conditions that could have provided predictability and the potential for early warning did not appear to play an appreciable role in this event. R. M. Dole M. P. Hoerling J. Perlwitz J. K. Eischeid P. Pegion T. Zhang X.-W. Quan T. Xu D. Murray 2012-11-13T18:25:37Z 2013-05-02T16:33:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/628 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/628 2012-11-13T18:25:37Z Numerical simulation of a synoptic event in the Southern California Bight In the middle of March 2002 a synoptic upwelling event occurred in the Southern California Bight; it was marked by a precipitous cooling of at least 4°C within 10–20 km of the coast. By the end of the month the preevent temperatures had slowly recovered. The Regional Oceanic Model System (ROMS) is used to simulate the event with an atmospheric downscaling reanalysis for surface wind and buoyancy flux forcing. Lateral boundary conditions of temperature, salinity, velocity, and sea level are taken from a global oceanic product. Barotropic tidal fields from a global barotropic model are imposed along the open boundaries. The simulation reproduces well the upwelling process compared with observed data. The sensitivity of the simulation is examined to wind resolution, heat flux, and tidal forcing. The oceanic response to the different wind resolutions converges at the level of the 6 km resolution, which is the finest scale present in the terrain elevation data set used in the atmospheric downscaling. The combination of an analytical diurnal cycle in the solar radiation and the empirical coupling with the instantaneous ROMS sea surface temperature produces a similar oceanic response to the downscaled heat flux. Tidal effects are significant in the upwelling evolution due to the increase in wind energy input through a quasi-resonant alignment of the wind and surface current, probably by chance. C. Dong J. C. McWilliams A. Hall M. Hughes 2012-09-26T16:36:35Z 2013-05-08T14:58:53Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/226 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/226 2012-09-26T16:36:35Z A 10 year climatology of Arctic cloud fraction and radiative forcing at Barrow, Alaska A 10 year record of Arctic cloud fraction and radiative forcing has been generated using data collected at the Atmospheric Radiation Measurement (ARM) North Slope of Alaska site and the nearby NOAA Barrow Observatory (BRW) from June 1998 to May 2008. The cloud fractions (CFs) derived from ARM radar-lidar and ceilometer measurements increase significantly from March to May (0.57→0.84), remain relatively high (∼0.80–0.9) from May to October, and then decrease from November to the following March (0.8→0.57), having an annual average of 0.76. These CFs are comparable to those derived from ground-based radar-lidar observations during the Surface Heat Budget of the Arctic Ocean experiment and from satellite observations over the western Arctic regions. The monthly means of estimated clear-sky and measured all-sky shortwave (SW)-down and longwave (LW)-down fluxes at the two facilities are almost identical with the annual mean differences less than 1.6 Wm−2. Values of LW cloud radiative forcing (CRF) are minimum (6 Wm−2) in March, then increase monotonically to reach maximum (63 Wm−2) in August, then decrease continuously to the following March. The cycle of SW CRF mirrors its LW counterpart with the greatest negative impact occurring during the snow-free months of July and August. On annual average, the negative SW CRFs and positive LW CRFs nearly cancel, resulting in annual average NET CRF of about 3.5 Wm−2 on the basis of the combined ARM and BRW analysis. Compared with other studies, we find that LW CRF does not change over the Arctic regions significantly, but NET CRFs change from negative to positive from Alaska to the Beaufort Sea, indicating that Barrow is at a critical latitude for neutral NET CRF. The sensitivity study has shown that LW CRFs increase with increasing cloud fraction, liquid water path, and radiating temperature with high positive correlations (0.8–0.9). Negative correlations are found for SW CRFs, but a strong positive correlation between SW CRF and surface albedo exists. X. Dong B. Xi K. Crosby C. N. Long R. S. Stone M. D. Shupe 2012-10-15T23:46:08Z 2013-05-07T17:31:22Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/306 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/306 2012-10-15T23:46:08Z The global ocean data assimilation experiment high-resolution sea surface temperature pilot project A new generation of integrated sea surface temperature (SST) data products are being provided by the Global Ocean Data Assimilation Experiment (GODAE) High-Resolution SST Pilot Project (GHRSST-PP). These combine in near–real time various SST data products from several different satellite sensors and in situ observations and maintain the fine spatial and temporal resolution needed by SST inputs to operational models. The practical realization of such an approach is complicated by the characteristic differences that exist between measurements of SST obtained from subsurface in-water sensors, and satellite microwave and satellite infrared radiometer systems. Furthermore, diurnal variability of SST within a 24-h period, manifested as both warm-layer and cool-skin deviations, introduces additional uncertainty for direct intercomparison between data sources and the implementation of data-merging strategies. The GHRSST-PP has developed and now operates an internationally distributed system that provides operational feeds of regional and global coverage high-resolution SST data products (better than 10 km and 6 h). A suite of online satellite SST diagnostic systems are also available within the project. All GHRSST-PP products have a standard format, include uncertainty estimates for each measurement, and are served to the international user community free of charge through a variety of data transport mechanisms and access points. They are being used for a number of operational applications. The approach will also be extended back to 1981 by a dedicated reanalysis project. This paper provides a summary overview of the GHRSST-PP structure, activities, and data products. For a complete discussion, and access to data products and services see the information online at www.ghrsst-pp.org. C. Donlon I. Robinson K. S. Casey J. Vazquez-Cuervo E. Armstrong O. Arino C. Gentemann D. May P. LeBorgne J. Piollé I. Barton H. Beggs D. J. S. Poulter C. J. Merchant A. Bingham S. Heinz A. Harris G. Wick B. Emery P. Minnett R. Evans D. Llewellyn-Jones C. Mutlow R. W. Reynolds H. Kawamura N. Rayner 2012-11-13T18:20:37Z 2013-05-02T16:32:29Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/627 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/627 2012-11-13T18:20:37Z The Dynamical Core, Physical Parameterizations, and Basic Simulation Characteristics of the Atmospheric Component AM3 of the GFDL Global Coupled Model CM3 The Geophysical Fluid Dynamics Laboratory (GFDL) has developed a coupled general circulation model (CM3) for the atmosphere, oceans, land, and sea ice. The goal of CM3 is to address emerging issues in climate change, including aerosol–cloud interactions, chemistry–climate interactions, and coupling between the troposphere and stratosphere. The model is also designed to serve as the physical system component of earth system models and models for decadal prediction in the near-term future—for example, through improved simulations in tropical land precipitation relative to earlier-generation GFDL models. This paper describes the dynamical core, physical parameterizations, and basic simulation characteristics of the atmospheric component (AM3) of this model. Relative to GFDL AM2, AM3 includes new treatments of deep and shallow cumulus convection, cloud droplet activation by aerosols, subgrid variability of stratiform vertical velocities for droplet activation, and atmospheric chemistry driven by emissions with advective, convective, and turbulent transport. AM3 employs a cubed-sphere implementation of a finite-volume dynamical core and is coupled to LM3, a new land model with ecosystem dynamics and hydrology. Its horizontal resolution is approximately 200 km, and its vertical resolution ranges approximately from 70 m near the earth's surface to 1 to 1.5 km near the tropopause and 3 to 4 km in much of the stratosphere. Most basic circulation features in AM3 are simulated as realistically, or more so, as in AM2. In particular, dry biases have been reduced over South America. In coupled mode, the simulation of Arctic sea ice concentration has improved. AM3 aerosol optical depths, scattering properties, and surface clear-sky downward shortwave radiation are more realistic than in AM2. The simulation of marine stratocumulus decks remains problematic, as in AM2. The most intense 0.2% of precipitation rates occur less frequently in AM3 than observed. The last two decades of the twentieth century warm in CM3 by 0.32°C relative to 1881–1920. The Climate Research Unit (CRU) and Goddard Institute for Space Studies analyses of observations show warming of 0.56° and 0.52°C, respectively, over this period. CM3 includes anthropogenic cooling by aerosol–cloud interactions, and its warming by the late twentieth century is somewhat less realistic than in CM2.1, which warmed 0.66°C but did not include aerosol–cloud interactions. The improved simulation of the direct aerosol effect (apparent in surface clear-sky downward radiation) in CM3 evidently acts in concert with its simulation of cloud–aerosol interactions to limit greenhouse gas warming. L. J. Donner B. L. Wyman R. S. Hemler . . . R. Pincus et al. 2016-04-11T21:49:03Z 2016-04-11T21:49:03Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1322 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1322 2016-04-11T21:49:03Z Phase-Specific Characteristics of Wintertime Clouds across a Midlatitude Mountain Range Observations from a series of frontal and postfrontal storms during the Colorado Airborne Multiphase Cloud Study (CAMPS) are combined to show transitions in cloud dynamics and microphysical statistics over a mountain range. During 10 flights in 2010 and 2011, along-wind, across-ridge transects over the Colorado Park Range are performed to statistically characterize air motion and microphysical conditions and their variability. Composite transect statistics show median vertical winds to be mostly upward windward of the ridge axis, and that cloud water concentration (CWC) and ice-particle number concentration are greatest near the ridge. Mixed-phase clouds were found throughout the study area, but increase in frequency by 70% relative to other cloud types in the vicinity of the range. Compared to ice-only clouds, mixed-phase clouds are associated with greater near-ridge increases in CWC and preferentially occur in regions with greater vertical wind variability or updrafts. Strong leeside reductions in CWC, the abundance of mixed-phase clouds, and number concentration of ice particles reflect the dominance of precipitation and particle mass loss processes, rather than cloud growth processes, downwind from the topographic barrier. On days in which the air column stability does not support lee subsidence, this spatial configuration is markedly different, with both ice- and liquid-water-bearing clouds appearing near the ridgeline and extending downwind. A case study from 9 January 2011 highlights mixed-phase regions in trapped lee waves, and in a near-ridgetop layer with evidence of low-altitude ice particle growth. S. W. Dorsi M. D. Shupe P. O. G. Persson D. E. Kingsmill L. M. Avallone 2015-10-07T19:10:09Z 2015-10-07T19:10:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1234 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1234 2015-10-07T19:10:09Z Dynamics of turbulence under the effect of stratification and internal waves The objective of this paper is to study the dynamics of small-scale turbulence near a pycnocline, both in the free regime and under the action of an internal gravity wave (IW) propagating along a pycnocline, using direct numerical simulation (DNS). Turbulence is initially induced in a horizontal layer at some distance above the pycnocline. The velocity and density fields of IWs propagating in the pycnocline are also prescribed as an initial condition. The IW wavelength is considered to be larger by the order of magnitude as compared to the initial turbulence integral length scale. Stratification in the pycnocline is considered to be sufficiently strong so that the effects of turbulent mixing remain negligible. The dynamics of turbulence is studied both with and without an initially induced IW. The DNS results show that, in the absence of an IW, turbulence decays, but its decay rate is reduced in the vicinity of the pycnocline, where stratification effects are significant. In this case, at sufficiently late times, most of the turbulent energy is located in a layer close to the pycnocline center. Here, turbulent eddies are collapsed in the vertical direction and acquire the "pancake" shape. IW modifies turbulence dynamics, in that the turbulence kinetic energy (TKE) is significantly enhanced as compared to the TKE in the absence of IW. As in the case without IW, most of the turbulent energy is localized in the vicinity of the pycnocline center. Here, the TKE spectrum is considerably enhanced in the entire wave-number range as compared to the TKE spectrum in the absence of IW. O. A. Druzhinin L. A. Ostrovsky 2014-01-08T21:09:58Z 2014-01-08T21:09:58Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/986 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/986 2014-01-08T21:09:58Z The study of the effect of small-scale turbulence on internal gravity waves propagation in a pycnocline This paper presents the results of modeling the interaction between internal waves (IWs) and turbulence using direct numerical simulation (DNS). Turbulence is excited and supported by a random forcing localized in a vertical layer separated from the pycnocline. The main attention is paid to the internal wave damping due to turbulence and comparison of the results with those obtained theoretically by using the semi-empirical approach. It is shown that the IW damping rate predicted by the theory agrees well with the DNS results when turbulence is sufficiently strong to be only weakly perturbed by the internal wave; however, the theory overestimates the damping rate of IWs for a weaker turbulence. The DNS parameters are matched to the parameters of the laboratory experiment, and an extrapolation to the oceanic scales is also provided. O. A. Druzhinin L. A. Ostrovsky S. S. Zilitinkevich 2012-11-13T18:27:50Z 2013-05-02T16:33:34Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/629 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/629 2012-11-13T18:27:50Z Modeling of the cloud and radiation processes observed during SHEBA Six microphysics schemes implemented in the climate version of the Environment Canada's Global Multiscale Environmental (GEM) model are used to simulate the cloud and radiation processes observed during Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment. The simplest microphysics scheme (SUN) has one prognostic variable: the total cloud water content. The second microphysics scheme (MLO) has 12 prognostic variables. The four other microphysics schemes are modified versions of MLO. A new parameterization for heterogeneous ice nucleation based on laboratory experiments is included in these versions of MLO. One is for uncoated ice nuclei (ML-NAC) and another is for sulfuric acid coated ice nuclei (ML-AC). ML-AC and ML-NAC have been developed to distinguish non-polluted and polluted air masses, the latter being common over the Arctic during winter and spring. A sensitivity study, in which the dust concentration is reduced by a factor 5, is also performed to assess the sensitivity of the results to the dust concentration in ML-AC-test and ML-NAC-test. Results show that SUN, ML-AC and ML-AC-test reproduce quite well the downward longwave radiation and cloud radiative forcing during the cold season. The good results obtained with SUN are due to compensating errors. It overestimates cloud fraction and underestimates cloud liquid water path during winter. ML-AC and ML-AC-test reproduces quite well all these variables and their relationships. MLO, ML-NAC and ML-NAC-test underestimate the cloud liquid water path and cloud fraction during the cold season, which leads to an underestimation of the downward longwave radiation at surface. During summer, all versions of the model underestimate the downward shortwave radiation at surface. ML-AC and ML-NAC overestimate the total cloud water during the warm season, however, they reproduce relatively well the relationships between cloud radiative forcing and cloud microstructure, which is not the case for the most simple scheme SUN. P. Du E. Girard A. K. Bertram M. D. Shupe 2012-10-15T23:46:13Z 2013-05-07T17:31:02Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/307 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/307 2012-10-15T23:46:13Z Transport of forest fire emissions from Alaska and the Yukon Territory to Nova Scotia during summer 2004 Emissions from forest fires in Alaska and the Yukon Territory were observed at Chebogue Point, Nova Scotia (43.7°N, 66.1°W), between 11 and 13 July 2004. Smoke aerosols were first detected in the free troposphere by a Raman lidar and extended up to 8 km altitude. The plume was not evident at the surface until the second day, when increases in CO, acetonitrile (CH3CN), benzene, and aerosol mass concentrations were observed by in situ instrumentation. Enhancement ratios for each species relative to CO agreed with the range of values from other measurements of the same plume. The surface aerosols had an elevated black carbon fraction relative to both CO and organic matter, and the ratio of black to organic carbon was higher than what is typically observed in fresh smoke. The emissions were tracked back to Alaska and the Yukon Territory using aerosol optical depth measurements from the Aqua MODIS satellite instrument, and the transport was reconstructed using the GEOS-Chem and FLEXPART atmospheric models. The analysis suggests that aerosols were injected into the atmosphere in proportion to CO and that aerosol removal processes were weak during the 7 to 9 day transit time in the free troposphere. Transport of the tracers to the ground was strongly connected to synoptic-scale features in the surface meteorology. T. J. Duck B. J. Firanski . . . A. B. White et al. 2015-11-19T21:34:10Z 2015-11-19T21:34:30Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1286 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1286 2015-11-19T21:34:10Z Current model capabilities for simulating black carbon and sulfate concentrations in the Arctic atmosphere: a multi-model evaluation using a comprehensive measurement data set The concentrations of sulfate, black carbon (BC) and other aerosols in the Arctic are characterized by high values in late winter and spring (so-called Arctic Haze) and low values in summer. Models have long been struggling to capture this seasonality and especially the high concentrations associated with Arctic Haze. In this study, we evaluate sulfate and BC concentrations from eleven different models driven with the same emission inventory against a comprehensive pan-Arctic measurement data set over a time period of 2 years (2008–2009). The set of models consisted of one Lagrangian particle dispersion model, four chemistry transport models (CTMs), one atmospheric chemistry-weather forecast model and five chemistry climate models (CCMs), of which two were nudged to meteorological analyses and three were running freely. The measurement data set consisted of surface measurements of equivalent BC (eBC) from five stations (Alert, Barrow, Pallas, Tiksi and Zeppelin), elemental carbon (EC) from Station Nord and Alert and aircraft measurements of refractory BC (rBC) from six different campaigns. We find that the models generally captured the measured eBC or rBC and sulfate concentrations quite well, compared to previous comparisons. However, the aerosol seasonality at the surface is still too weak in most models. Concentrations of eBC and sulfate averaged over three surface sites are underestimated in winter/spring in all but one model (model means for January–March underestimated by 59 and 37 % for BC and sulfate, respectively), whereas concentrations in summer are overestimated in the model mean (by 88 and 44 % for July–September), but with overestimates as well as underestimates present in individual models. The most pronounced eBC underestimates, not included in the above multi-site average, are found for the station Tiksi in Siberia where the measured annual mean eBC concentration is 3 times higher than the average annual mean for all other stations. This suggests an underestimate of BC sources in Russia in the emission inventory used. Based on the campaign data, biomass burning was identified as another cause of the modeling problems. For sulfate, very large differences were found in the model ensemble, with an apparent anti-correlation between modeled surface concentrations and total atmospheric columns. There is a strong correlation between observed sulfate and eBC concentrations with consistent sulfate/eBC slopes found for all Arctic stations, indicating that the sources contributing to sulfate and BC are similar throughout the Arctic and that the aerosols are internally mixed and undergo similar removal. However, only three models reproduced this finding, whereas sulfate and BC are weakly correlated in the other models. Overall, no class of models (e.g., CTMs, CCMs) performed better than the others and differences are independent of model resolution. S. Eckhardt B. Quennehen D. J. L. Olivié . . . S. Crepinsek et al. 2017-01-03T17:08:19Z 2017-01-03T17:08:19Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1452 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1452 2017-01-03T17:08:19Z Multi-method attribution analysis of extreme precipitation in Boulder, Colorado Understanding and attributing the characteristics of extreme events that lead to societal impacts is a key challenge in climate science. Detailed analysis of individual case studies is particularly important in assessing how anthropogenic climate change is changing the likelihood of extreme events and their associated risk at relevant spatial scales. Here, we conduct a comprehensive multi-method attribution analysis of the heavy precipitation that led to widespread flooding in Boulder, Colorado in September 2013. We provide clarification on the source regions of moisture associated with this event in order to highlight the difficulty of separating dynamic and thermodynamic contributions. Using extreme value analysis of, first of all, historical observations, we then assess the influence of anthropogenic climate change on the overall likelihood of one- and five-day precipitation events across the Boulder area. The same analysis is extended to the output of two general circulation model ensembles. By combining the results of different methods we deduce an increase in the likelihood of extreme one-day precipitation but of a smaller magnitude than what would be expected in a warming world according to the Clausius–Clapeyron relation. For five-day extremes, we are unable to detect a change in likelihood. Our results demonstrate the benefits of a multi-method approach to making robust statements about the anthropogenic influence on changes in the overall likelihood of such an event irrespective of its cause. We note that, in this example, drawing conclusions solely on the basis of thermodynamics would have overestimated the increase in risk. J. M. Eden K. Wolter F. E. L. Ottto G. J. van Oldenborgh 2012-06-29T15:18:14Z 2013-05-02T16:15:03Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/44 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/44 2012-06-29T15:18:14Z Direct covariance measurement of CO2 gas transfer velocity during the 2008 Southern Ocean Gas Exchange Experiment: Wind speed dependency Direct measurements of air-sea heat, momentum, and mass (including CO2, DMS, and water vapor) fluxes using the direct covariance method were made over the open ocean from the NOAA R/V Ronald H. Brown during the Southern Ocean Gas Exchange (SO GasEx) program. Observations of fluxes and the physical processes associated with driving air-sea exchange are key components of SO GasEx. This paper focuses on the exchange of CO2 and the wind speed dependency of the transfer velocity, k, used to model the CO2 flux between the atmosphere and ocean. A quadratic dependence of k on wind speed based on dual tracer experiments is most frequently encountered in the literature. However, in recent years, bubble-mediated enhancement of k, which exhibits a cubic relationship with wind speed, has emerged as a key issue for flux parameterization in high-wind regions. Therefore, a major question addressed in SO GasEx is whether the transfer velocities obey a quadratic or cubic relationship with wind speed. After significant correction to the flux estimates (primarily due to moisture contamination), the direct covariance CO2 fluxes confirm a significant enhancement of the transfer velocity at high winds compared with previous quadratic formulations. Regression analysis suggests that a cubic relationship provides a more accurate parameterization over a wind speed range of 0 to 18 m s−1. The Southern Ocean results are in good agreement with the 1998 GasEx experiment in the North Atlantic and a recent separate field program in the North Sea. J. Edson C. W. Fairall L. Bariteau C. Zappa A. Cifuentes-Lorenzen W. R. McGillis S. Pezoa J. Hare D. Helmig 2014-01-09T01:33:08Z 2014-01-09T01:33:08Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1015 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1015 2014-01-09T01:33:08Z On the Exchange of Momentum over the Open Ocean This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s−1) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m−1 s and b = −0.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s−1. Wave age– and wave slope–dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed–dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed–, wave age–, and wave slope–dependent formulations give similar results—the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s−1. J. B. Edson V. Jampana R. A. Weller . . . C. W. Fairall et al. 2015-04-27T16:11:22Z 2015-10-07T19:13:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1164 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/1164 2015-04-27T16:11:22Z High winter ozone pollution from carbonyl photolysis in an oil and gas basin The United States is now experiencing the most rapid expansion in oil and gas production in four decades, owing in large part to implementation of new extraction technologies such as horizontal drilling combined with hydraulic fracturing. The environmental impacts of this development, from its effect on water quality1 to the influence of increased methane leakage on climate2, have been a matter of intense debate. Air quality impacts are associated with emissions of nitrogen oxides3, 4 (NOx = NO + NO2) and volatile organic compounds5, 6, 7 (VOCs), whose photochemistry leads to production of ozone, a secondary pollutant with negative health effects8. Recent observations in oil- and gas-producing basins in the western United States have identified ozone mixing ratios well in excess of present air quality standards, but only during winter9, 10, 11, 12, 13. Understanding winter ozone production in these regions is scientifically challenging. It occurs during cold periods of snow cover when meteorological inversions concentrate air pollutants from oil and gas activities, but when solar irradiance and absolute humidity, which are both required to initiate conventional photochemistry essential for ozone production, are at a minimum. Here, using data from a remote location in the oil and gas basin of northeastern Utah and a box model, we provide a quantitative assessment of the photochemistry that leads to these extreme winter ozone pollution events, and identify key factors that control ozone production in this unique environment. We find that ozone production occurs at lower NOx and much larger VOC concentrations than does its summertime urban counterpart, leading to carbonyl (oxygenated VOCs with a C = O moiety) photolysis as a dominant oxidant source. Extreme VOC concentrations optimize the ozone production efficiency of NOx. There is considerable potential for global growth in oil and gas extraction from shale. This analysis could help inform strategies to monitor and mitigate air quality impacts and provide broader insight into the response of winter ozone to primary pollutants. P. E. Edwards S. S. Brown J. M. Roberts . . . R. J. Zamora 2012-10-15T23:46:24Z 2013-05-07T17:30:39Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/309 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/309 2012-10-15T23:46:24Z Angular momentum in the global atmospheric circulation Angular momentum is a variable of central importance to the dynamics of the atmosphere both regionally and globally. Moreover, the angular momentum equations yield a precise description of the dynamic interaction of the atmosphere with the oceans and the solid Earth via various torques as exerted by friction, pressure against the mountains and the nonspherical shape of the Earth, and by gravity. This review presents recent work with respect to observations and the theory of atmospheric angular momentum of large-scale motions. It is mainly the recent availability of consistent global data sets spanning decades that sparked renewed interest in angular momentum. In particular, relatively reliable estimates of the torques are now available. In addition, a fairly wide range of theoretical aspects of the role of angular momentum in atmospheric large-scale dynamics is covered. J. Egger K. M. Weickmann K.-P. Hoinka 2012-10-15T23:46:19Z 2013-05-07T17:30:48Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/308 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/308 2012-10-15T23:46:19Z Latitude–Height Structure of the Atmospheric Angular Momentum Cycle Associated with the Madden–Julian Oscillation The angular momentum cycle of the Madden–Julian oscillation is analyzed by regressing the zonally averaged axial angular momentum (AAM) budget including fluxes and torques against the first two principal components P1 and P2 of the empirical orthogonal functions (EOFs) of outgoing longwave radiation (OLR). The maximum of P1 coincides with an OLR minimum near 150°E and a shift from anomalously negative AAM to positive AAM in the equatorial troposphere. AAM anomalies of one sign develop first in the upper-equatorial troposphere and then move downward and poleward to the surface of the subtropics within two weeks. During the same time the opposite sign AAM anomaly develops in the upper-equatorial troposphere. The tropical troposphere is warming when P1 approaches its maximum while the stratosphere is cooling. The torques are largest in the subtropics and are linked with the downward and poleward movement of AAM anomalies. The evolution is conveniently summarized using a time–height depiction of the global mean AAM and vertical flux anomaly. J. Egger K. Weickmann 2012-11-13T21:15:21Z 2013-05-08T18:02:09Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/654 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/654 2012-11-13T21:15:21Z Antarctic Tropospheric Chemistry Investigation (ANTCI) 2003 overview The Antarctic Tropospheric Chemistry Investigation (ANTCI) was carried out from late November to December 2003 with both extended ground-based and tethered balloon studies at Amundsen Scott Station, South Pole. ANTCI 2003 was the first of two Antarctic field studies with the primary goal of further exploring the active photochemistry of the South Pole region that was first identified in the previous Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) program. Since ISCAT was fully ground-based, ANTCI 2003 goals included expanding chemical studies both vertically upward to investigate mixing and horizontally to better understand large-scale plateau NOx production and transport. Thus, in addition to ground-based experiments at South Pole, Twin Otter aircraft sampling took place out to hundreds of kilometers in several directions from the South Pole. These were designed to specifically address the issue of how representative past South Pole chemical measurements are of the surrounding high plateau region. The Twin Otter was also used to make transects along the coast both north and south of McMurdo Station. The present paper summarizes the overall setting and results of this investigation and highlights the many new findings that were obtained. F. Eisele D. D. Davis D. Helmig S. Oltmans W. Neff et al. 2012-11-14T21:32:49Z 2013-08-26T22:28:18Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/718 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/718 2012-11-14T21:32:49Z Projection of changes in the frequency of heavy rain events over Hawaii based on leading Pacific climate modes This study investigates the frequency of heavy rainfall events in Hawaii during the wet season (October-April) 1958–2005 and their conditional dependence on the Pacific-North American (PNA) pattern and El Niño-Southern Oscillation (ENSO). Heavy rain events are defined by the 95% quantile in the rainfall distribution of the wet seasons. Twelve stations with daily reports of rainfall amounts were used to count the number of heavy rain days during wet seasons. Multiple linear regression (MLR) indicated that the PNA index (PNAI) and the Southern Oscillation Index (SOI) can explain a significant amount of the interannual to interdecadal variability for 9 out of 12 stations. Cross validation showed that PNAI and SOI together explain about 18–44% of the variability in the number of heavy rain events. Furthermore, the MLR model reproduces the trend toward fewer heavy rain events in the years after the Pacific climate shift in the mid-1970s. The MLR model was applied to the projected PNAI and SOI indices that were obtained from six IPCC AR4 climate models. The current suite of AR4 simulations based on the A1B and A2 emissions scenarios projects small and equivocal changes in the mean state of the SOI and PNAI during the 21st century. The covariance between PNAI and SOI in these simulations appears to be stable. To the extent that variations in the frequency and magnitude of ENSO and the PNA mode are responsible for modulating extreme rainfall occurrence in Hawaii, our results indicate small changes in the projected number of heavy rainfall days with large uncertainties resulting from disparities among the climate models. O. Elison Timm H. F. Diaz T. W. Giambelluca M. Takahashi 2013-08-26T22:20:29Z 2013-08-26T22:26:51Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/949 This item is in the repository with the URL: https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/949 2013-08-26T22:20:29Z On the relation between large-scale circulation pattern and heavy rain events over the Hawaiian Islands: Recent trends and future changes The aim of this paper is to present a statistical downscaling method in which the relationships between present-day daily weather patterns and local rainfall data are derived and used to project future shifts in the frequency of heavy rainfall events under changing global climate conditions. National Centers for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) reanalysis data from wet season months (November to April) 1958–2010 are composited for heavy rain days at 12 rainfall stations in the Hawaiian Islands. The occurrence of heavy rain events (days with amounts above the 90th percentile estimated from all wet season rain days 1958–2010) was found to be strongly correlated with upper level cyclonic circulation anomalies centered northwest of Hawai'i and south-to-north transport of water vapor in the middle troposphere. The statistical downscaling model (SD) developed in this study was able to reproduce the observed interannual variations in the number of heavy rain events based on cross-validation resampling during the more recent interval 1978–2010. However, multidecadal changes associated with the mid-1970s' climate shift were not well reproduced by the SD using NCEP/NCAR reanalysis data, likely due to inhomogenities in the presatellite period of the NCEP/NCAR reanalysis. Application of the SD to two model scenarios from the CMIP3 database indicates a reduction of heavy rain events in the mid- to late 21st century. Based on these models, the likelihood of a widespread increase in synoptic heavy rain events in Hawai'i as a result of anthropogenic climate change is low over the remainder of the century. O. Elison Timm M. Takahashi T. W. Giambelluca H. F. Diaz 2012-10-15T23:46:30Z 2013-08-27T21:44:16Z https://www.esrl.noaa.gov:80/psd/pubs/id/eprint/311