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NASA Technical Reports Server (NTRS)
In situ sampling of the crystals is described with a NASA high-altitude aircraft to characterize the presence of ice particles and their role in Antarctic ozone chemistry. A NASA wire impactor was employed to collect the crystals, and the device was modified to permit Formvar crystal replication. The size distributions of the columnar crystals show that at the highest altitude the the smallest crystals are collected. The crystals provide surface area for heterogeneous chemical reactions as well as the removal of moisture and particles from the stratosphere and its ozone-related components.
Goodman, Jindra; Pueschel, R. F.; Snetsinger, K. G.; Verma, S.
Bacterial ice crystal controlling proteins.
Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057
Lorv, Janet S H; Rose, David R; Glick, Bernard R
Bacterial Ice Crystal Controlling Proteins
Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions.
Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.
Cluster self-organization of intermetallic systems: Quasi-spherical nanocluster precursors with internal Friauf polyhedra (A-172) and icosahedra (B-137) in the Li{sub 19}Na{sub 8}Ba{sub 15} (hP842) crystal structure
A combinatorial and topological analysis of Li{sub 19}Na{sub 8}Ba{sub 15} (hP842, a = 20 A, c = 93 A, V = 33552 A{sup 3}, P3-bar) has been performed using computer methods (the TOPOS program package). Two types of crystal-forming quasi-spherical nanoclusters about 20 A in diameter with internal Friauf polyhedra (A-172) and icosahedra (B-137) have been established by the complete decomposition of the 3D factor graph of the structure into cluster substructures. Each type of nanoclusters forms close-packed 2D layers 3{sup 6}, which alternate along the c axis. The B-137 and A-172 nanoclusters are composed of three layers and have shell compositions (1 + 12 + 32 + 92) and (1 + 16 + 59 + 103) with local symmetries 3 and 3-bar, respectively; they were revealed for the first time in crystal structures as cluster precursors. The icosahedral B-137 nanocluster contains a 104-atom quasicrystal approximant (Samson cluster).
Ilyushin, G. D., E-mail: email@example.com [Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation); Blatov, V. A. [Samara State University (Russian Federation)
Supernumerary ice-crystal halos?
Geometric-optics singularities in the intensity profiles of refraction halos formed by randomly oriented ice crystals are softened by diffraction and decorated with fine supernumerary fringes. If the crystals have a fixed symmetry axis (as in parhelia), the geometric singularity is a square-root divergence, as in the rainbow. However, the universal curve that describes diffraction is different from the rainbow's Airy
Michael V. Berry
Current implosion of quasi-spherical wire arrays
NASA Astrophysics Data System (ADS)
By means of the electrostatic expansion of a cylindrical wire array by an additional electrode, quasi-spherical arrays with a radius of 8-12 mm and a mass of 200-400 ?g consisting of 30-60 tungsten wires 6 ?m in thickness are formed. The compression of Z pinches formed by these arrays was performed by a current of 3-4 MA with a rise time of 100 ns in the Angara-5-1 facility. It has been shown that the central part of this array forms a region hotter than its edges and that for cylindrical arrays.
Grabovskii, E. V.; Gritsuk, A. N.; Smirnov, V. P.; Aleksandrov, V. V.; Oleinik, G. M.; Frolov, I. N.; Laukhin, Ya. N.; Gribov, A. N.; Samokhin, A. A.; Sasorov, P. V.; Mitrofanov, K. N.; Medovshchikov, S. F.
Quasi-spherical Approach (III): Treatment of the Earth's Center
NASA Astrophysics Data System (ADS)
We have worked to construct an accurate and efficient method for seismic waveform modeling for a laterally heterogeneous global earth. In the field of global seismology, the axisymmetric modeling which assumes structures to be axisymmetric about the axis through the source and solves the elastodynamic equation in spherical coordinates, has been an efficient modeling method. Although it can correctly model the geometrical spreading effects in 3D with computational resources comparable to 2D modeling, the conventional axisymmetric modeling cannot treat asymmetric (realistic) structures with respect to the source axis. In order to overcome this problem, the quasi-spherical finite-difference method (FDM) has been developed (Toyokuni et al., AGU Fall Meeting, 2004; Toyokuni et al., GRL, 2005). This method can model seismic wave propagation in a 2D slice of a global earth model with an arbitrary lateral heterogeneity, with a similar computation time and storage as for 2D modeling. We then implemented an arbitrary moment tensor sources into the quasi-spherical FDM scheme (Toyokuni et al., WPGM, 2006). However, these schemes could not treat the center of the earth due to the singularity at this point. This time, we extend the quasi-spherical FDM to be able to model seismic wave propagation through the earth's center. To achieve this, we introduce a discontinuous grid (Aoi &Fujiwara, BSSA, 1999) in the lateral direction, while we use non-uniform grid in the radial direction. For discontinuous change of the lateral grid spacing, the grid in the deeper region is set to have three times coarser interval than in the upper region. Wavefields from the deeper layer are passed to the upper layer through the fourth-order Lagrange interpolation. Then wavefields at the earth's center are evaluated also using Lagrange interpolation from the values around the center. In this presentation, we show some numerical examples to demonstrate the validity and feasibility of our method. In addition, there is another interpolation technique that uses Fourier interpolation with FFT for the multidomain scheme (Wang &Takenaka, EPS, 2001). We will also apply it to our calculation and discuss the results.
Toyokuni, G.; Takenaka, H.; Wang, Y.; Kennett, B. L.
Evolution of crystal fabric: Ice-Age ice versus Holocene ice
Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric
J. H. Kennedy; E. C. Pettit
Modeling Commercial Turbofan Engine Icing Risk With Ice Crystal Ingestion
NASA Technical Reports Server (NTRS)
The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in flight. The computational tool was utilized to help guide a portion of the PSL testing, and was used to predict ice accretion could also occur at significantly lower altitudes. The predictions were qualitatively verified by subsequent testing of the engine in the PSL. The PSL test has helped to calibrate the engine icing computational tool to assess the risk of ice accretion. The results from the computer simulation identified prevalent trends in wet bulb temperature, ice particle melt ratio, and engine inlet temperature as a function of altitude for predicting engine icing risk due to ice crystal ingestion.
Jorgenson, Philip C. E.; Veres, Joseph P.
Retardation of ice crystallization by short peptides
The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice\\/water interface is observed
Jun Soo Kim; Arun Yethiraj
Structure of ice crystallized from supercooled water
The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples.
Malkin, Tamsin L.; Murray, Benjamin J.; Brukhno, Andrey V.; Anwar, Jamshed; Salzmann, Christoph G.
Simulation of quasi-spherical shell implosions on Z for inertial confinement fusion
The magnetic implosion of a high-Z quasi-spherical shell filled with DT fuel by the 20-MA Z accelerator can heat the fuel to near-ignition temperature. The attainable implosion velocity on Z for an 8 mm diameter quasi-spherical shell, 13-cm\\/5s, is fast enough that thermal losses from the fuel to the shell are small. The fuel is initially heated by an ion
T. J. Nash; M. R. Douglas
Colloidal crystallization utilizing interfaces of unidirectionally growing ice crystals
NASA Astrophysics Data System (ADS)
We show the possibility of unidirectional freezing of colloidal random suspensions as a novel method for growing colloidal crystals. First we confirmed the rejection of polystyrene particles from unidirectionally growing ice-water interfaces by observing color gradations of colloidal crystals formed in front of the interfaces. The rejection of particles from the growing interfaces increased particle concentration in the colloidal crystals. Then we succeeded in achieving colloidal crystallization in front of ice-water interfaces during the unidirectional freezing of water suspensions of polystyrene particles. The colloidal crystals thus obtained exhibited a columnar shape that is typically observed in the unidirectional colloidal crystallization using centrifugation.
Suzuki, Yoshihisa; Sazaki, Gen; Hashimoto, Kaori; Fujiwara, Takahisa; Furukawa, Yoshinori
Retardation of ice crystallization by short peptides
NASA Astrophysics Data System (ADS)
The effect of short peptides on the growth of ice crystals is studied using molecular dynamics simulations. The simulations focus on two sequences (Gly-Pro-Ala-Gly and Gly-Gly-Ala-Gly) that are found in collagen hydrolysate, a substance that is known to retard crystal growth. In the absence of peptides, the growth of ice crystal in the solution with the ice/water interface is observed in at a rate comparable to the experimental data. When peptides are present in the liquid phase, the crystal growth is retarded to a significant extent compared to the pure water. It is found that Gly-Pro-Ala-Gly is more effective (crystallization is up to 5 times slower than in its absence) than Gly-Gly-Ala-Gly (up to 3 times slower) implying that the role of the proline residue is important. The mechanism can be understood in the nature of binding of the peptides to the growing crystal.
Kim, Jun Soo; Yethiraj, Arun
Design, simulation, and application of quasi-spherical z-pinch implosions driven by tens of mega-amperes.
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28 MA 100 ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Struve, Kenneth William; Deeney, Christopher D.; Leeper, Ramon Joe; McDaniel, Dillon Heirman; Nash, Thomas J.; DeGroot, John Stacey; Sanford, Thomas W. L.
Evolution of crystal fabric: Ice-Age ice versus Holocene ice
NASA Astrophysics Data System (ADS)
Ice-Age ice has smaller crystals and higher concentrations of impurities than Holocene ice; these properties cause it to develop a more strongly-aligned crystal-orientation fabric. In many regions of the Antarctic and Greenland ice sheets, the Ice-Age ice is now at depth and its flow properties may dominate the ice flow patterns, particularly where sliding is minimal. We use a fabric evolution model, based on that developed by Thorsteinsson (2002), to explore the evolution of Ice-Age ice fabric along particle paths for ice within Taylor Glacier, a cold-based outlet glacier of the East Antarctic Ice Sheet. The bulk of the ice within Taylor Glacier consists of Ice-Age and older ice because the Holocene ice has ablated away (there is no Holocene ice remaining within 25km of the terminus, Aciego, 2007). We initialize the evolving fabric based on fabric measurements from Taylor Dome where available (DiPrinzio, 2003) and other ice core records. We compare model results with thin-section data from shallow cores taken near the terminus. As expected, crystal alignment strengthens along the ice particle path. Due to lateral shearing along valley walls and the ice cliffs (terminal ice cliffs are cold in winter and present a resistance to flow), a tilted single maximum is common near the terminus. The highly-aligned fabric of Ice-Age ice is significantly softer than Holocene ice in simple shear parallel to the bed, this softness not only results in faster flow rates for glaciers and ice sheets such as Taylor, but creates a climate-flow-fabric feedback loop through concentrating ice-sheet flow within the Ice-Age ice. Thorsteinsson, T. (2002), Fabric development with nearest-neighbor interaction and dynamic recrystallization, J. Geophys. Res., 107(B1), 2014, doi:10.1029/2001JB000244. S.M. Aciego, K.M. Cuffey, J.L. Kavanaugh, D.L. Morse, J.P. Severinghaus, Pleistocene ice and paleo-strain rates at Taylor Glacier, Antarctica, Quaternary Research, Volume 68, Issue 3, November 2007, Pages 303-313, ISSN 0033-5894, DOI: 10.1016/j.yqres.2007.07.013. DiPrinzio, Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract C11C-0834, 2003
Kennedy, J. H.; Pettit, E. C.
Ice crystals in high clouds and contrails
NASA Astrophysics Data System (ADS)
In honor of Dr. Helmut K. Weickmann's lifetime achievements, some of his early discoveries on ice crystals in high clouds are resurrected and discussed. It is demonstrated that the shapes and sizes of cloud meteors convey information related to cloud type, cloud duration, cloud amount, cloud radiative forcing, and the environment in which the cloud forms. For example, persistence of a contrail behind an aircraft depends on ice crystal concentration and size distribution, which are governed by the ambient temperature, humidity, and the concentration of ice nuclei. It is suggested that increased air traffic, especially high-flying jets over the past three decades, may have modified global cirrus cloud amount, which in turn may affect surface temperature and global climate.
Parungo, F.
Dynamics of quasi-spherical Z-pinch implosions with mass redistribution and displacement modification
Implosions of (quasi-)spherical loads with mass redistribution and displacement modification are investigated numerically. Both methods can theoretically counterbalance the nonuniformity of magnetic pressure along the load surface and realize quasi-spherical Z-pinch implosions. Mass redistribution is feasible for spherical loads with large radius and weight, while the displacement modification is more suitable for light loads, such as those composed of wire arrays. Simulation results suggest that, for mass redistributed spherical loads, wall instabilities induced by polar mass flows will deform the imploding shell. For prolate spherical loads, in which the wall instability cannot develop, the kinetic energy distribution is disturbed at high latitude. These passive behaviors and their possible mitigation methods, such as reshaping the electrode, are investigated numerically in this paper.
Zhang Yang [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009-09, Beijing 100094 (China); Institute of Nuclear Physics and Chemistry, P. O. Box 919-212, Mianyang 621900 (China); Ding Ning; Sun Shunkai; Xue Chuang; Ning Cheng; Xiao Delong; Huang Jun [Institute of Applied Physics and Computational Mathematics, P. O. Box 8009-09, Beijing 100094 (China); Li Zhenghong [Institute of Nuclear Physics and Chemistry, P. O. Box 919-212, Mianyang 621900 (China)
Spectral collocation methods for solution of Einstein's equations in null quasi-spherical coordinates
The spectral methods which are being used to solve Einstein's equations innull quasi-spherical coordinates are described. They include Fast Fourier methodsfor evaluating derivatives in a uniform grid representation and methods for transformingto and from spin-weighted spherical harmonic representations. In theory,expressions involving spherical harmonics up to any fixed maximum angular momentum L can be routinely manipulated with accuracy depending only on
Andrew H. Norton
Adiabatic Quasi-Spherical Compressions Driven by Magnetic Pressure for Inertial Confinement Fusion
The magnetic implosion of a high-Z quasi-spherical shell filled with DT fuel by the 20-MA Z accelerator can heat the fuel to near-ignition temperature. The attainable implosion velocity on Z, 13-cm\\/μs, is fast enough that thermal losses from the fuel to the shell are small. The high-Z shell traps radiation losses from the fuel, and the fuel reaches a high
Thomas J. Nash; THOMAS J
Disturbed basal ice seen in radio echo images coincide with zones of big interlocking ice crystals.
NASA Astrophysics Data System (ADS)
Improvement of the depth sounding radio echo sounding (RES) over Antarctica and Greenland Ice Sheet has made it possible to map the near basal layers that have not been 'seen' earlier due to the very high demand of attenuation needed to reach through more than 3000m of ice. The RES internal reflectors show that the near basal ice at many locations has disturbed layering. At the locations where ice cores reach the bedrock both in Greenland and Antarctica studies of the ice crystal size and orientation show that the near basal ice has big and interlocking ice crystals which suggests the ice is not actively deforming. These observations challenge the often used constitutive equations like Glens flow law in ice sheet modelling. A discussion of the impact of the RES findings on ice sheet modeling and the quest to find the oldest ice in Antarctic based on the anisotropy of the basal ice will follow.
Dahl-Jensen, Dorthe; Gogineni, Sivaprasad; Panton, Christian
Modeling, simulation, and comparison study of cirrus cloud ice crystals
Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured
Jorge M. Villa; Sandra L. Cruz-Pol; Jose G. Colom-Ustariz; Stephen M. Sekelsky
Modeling, Simulation and Comparison Study of Cirrus Clouds' Ice Crystals
Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured
Jorge M. Villa; Sandra L. Cruz-Pol; Jos� Colom-Ust�riz; Stephen M. Sekelsky
Quasi-spherical microwells on superhydrophobic substrates for long term culture of multicellular spheroids and high throughput assays.
Multicellular tumour spheroids closely recapitulate the physiological environment of tumour tissues. However, their implementation in drug screening assays remains limited due to the technological challenges of forming large numbers of high quality spheroids in platforms compatible with high throughput screening. A simple bench-top microfabrication strategy is demonstrated here based on the principle of ice lithography carried out on superhydrophobic substrates to fabricate quasi-spherical microwells (spheriwells). The microwells shapes and dimensions are directly controlled by the hydrophobicity of the substrate and the volume of the water droplets. The prepared concave microwells enable the formation of dense and homogeneous multicellular tumour spheroids. Spheroids formed within spheriwells are trapped within the microwells, which eliminate loss during media manipulation and facilitate long-term on-chip culture. Morphological and phenotypical changes associated with the growth of MCF-7 adenocarcinoma cells in spheriwells were characterised using imaging flow cytometry and revealed the appearance of heterogeneous populations with loss of E-Cadherin expression. The compatibility of the spheriwells with an on-chip MTT assay is demonstrated. The very unusual shape of the spheriwells, prepared using materials and methods routinely used in most research laboratories, provides a straightforward and scalable platform to prepare high quality multicellular tumour spheroids compatible with high throughput biological screening assays. PMID:24797879
Liu, Tianqing; Winter, Marnie; Thierry, Benjamin
Specular scattering by preferentially oriented ice crystals.
Scattered light for preferentially oriented ice crystals is divided into specular and diffuse components, where the specular scattering is created by horizontally oriented facets of fluttering crystals. The specular component for a fluttering thin plate modeling these crystals is found analytically. The solution obtained is a two-dimensional (2D) convolution of a geometric optics pattern depending only on flutter and an independent diffraction function. The geometric optics pattern is explicitly expressed through the probability density for particle tilts, and the diffraction function is taken in the Fraunhofer diffraction approximation. The 2D convolution calculated numerically reveals a cumulative enhancement of scattered light in the scattering domain center. Certain possibilities to retrieve both flutter parameters and particle sizes from the specular patterns are discussed. PMID:19571949
Borovoi, Anatoli; Kustova, Natalia
Factors Affecting the Changes of Ice Crystal Form in Ice Cream
NASA Astrophysics Data System (ADS)
In this study, the shape of ice crystals in ice cream was quantitatively evaluated by introducing fractal analysis. A small droplet of commercial ice cream mix was quickly cooled to about -30�C on the cold stage of microscope. Subsequently, it was heated to -5�C or -10�C and then held for various holding time. Based on the captured images at each holding time, the cross-sectional area and the length of circumference for each ice crystal were measured to calculate fractal dimension using image analysis software. The results showed that the ice crystals were categorized into two groups, e.g. simple-shape and complicated-shape, according to their fractal dimensions. The fractal dimension of ice crystals became lower with increasing holding time and holding temperature. It was also indicated that the growing rate of complicated-shape ice crystals was relatively higher because of aggregation.
Wang, Xin; Watanabe, Manabu; Suzuki, Toru
Growth control of ice crystals by poly(vinyl alcohol) and antifreeze protein in ice slurries
Effect of poly(vinyl alcohol) (PVA) in inhibiting an increase in ice crystal size in isothermal ice slurries was investigated, and then compared with the effect of an antifreeze protein (AFP), NaCl, and three other polymers, namely, poly(ethylene glycol), poly(vinyl pyrrolidone), and poly(acrylic acid). First, ice slurries, in which the initial size distribution of ice crystals was known, were isothermally preserved
Takaaki Inada; Poly Rani Modak
Augmentation of Radiation Intensity in Quasi-Spherical Double Liner/Dynamic Hohlraum
NASA Astrophysics Data System (ADS)
To increase the conversion efficiency of magnetic energy to radiation in Double Liner/Dynamic-Hohlraum and to approach closer to the ignition conditions we proposed the concept of implosion of a quasi-spherical double liner. The almost spherical implosion can be realized with a special mass distribution in liners. Axial cumulating of liner kinetic energy and more efficient radiation energy confinement allow augmentation of radiation intensity on the capsule with respect to cylindrical case under the same driver conditions. A controllable mass redistribution inside the nested external liner allows significant reduction and correction of distortions produced by the Rayleigh-Taylor instability. A phenomenon of energy confinement and enhancement of radiation intensity is considered and compared with the cylindrical case. On the basis of the developed physical model of non-LTE plasma using the RMHD code ZETA the dynamics of quasi-spherical Double Liner/Dynamic-Hohlraum and generation of radiation in two-dimensional geometry is examined and liner configuration is optimized.
Zakharov, S. V.; Smirnov, V. P.
Design, simulation, and application of quasi-spherical 100 ns z-pinch implosions driven by tens of mega-amperes
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28 MA 100 ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Nash, T.J.; McDaniel, D.H.; Leeper, R.J.; Deeney, C.D.; Sanford, T.W.L.; Struve, K.; DeGroot, J.S. [Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
The structure of ice crystallized from supercooled water
NASA Astrophysics Data System (ADS)
The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice Isd). This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice Ih) in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed.
Murray, Benjamin
Quasi-spherical direct drive fusion simulations for the Z machine and future accelerators.
We explored the potential of Quasi-Spherical Direct Drive (QSDD) to reduce the cost and risk of a future fusion driver for Inertial Confinement Fusion (ICF) and to produce megajoule thermonuclear yield on the renovated Z Machine with a pulse shortening Magnetically Insulated Current Amplifier (MICA). Analytic relationships for constant implosion velocity and constant pusher stability have been derived and show that the required current scales as the implosion time. Therefore, a MICA is necessary to drive QSDD capsules with hot-spot ignition on Z. We have optimized the LASNEX parameters for QSDD with realistic walls and mitigated many of the risks. Although the mix-degraded 1D yield is computed to be {approx}30 MJ on Z, unmitigated wall expansion under the > 100 gigabar pressure just before burn prevents ignition in the 2D simulations. A squeezer system of adjacent implosions may mitigate the wall expansion and permit the plasma to burn.
VanDevender, J. Pace; McDaniel, Dillon Heirman; Roderick, Norman Frederick; Nash, Thomas J.
Processes causing electrification of ice crystals in thunderclouds
NASA Astrophysics Data System (ADS)
Jayaratne and Saunders (1991) have performed a useful service by reporting their laboratory experiments demonstrating, contrary to the findings of Odencrantz and Buecher (1967), that ice crystal charging does not take place in an unmixed cloud of ice crystals. Jayaratne and Saunders' further cold box experiments showing that the ice crystals become electrified when a fan in the cold box is turned on, support their view that an ice-ice charging process takes place on the surfaces of the moving ice-covered fan-blades. Their conclusion, that this phenomenon might be capable of producing each second the several coulombs of charged cloud particles necessary to maintain the electrification of a thundercloud, appears justified. However, because their paper is lacking in experimental details and because it is unknown whether the conditions in their cold chamber accurately duplicate those in a thunderstorm, this point is not possible to resolve. There is good reason to doubt J and S's final conclusion, that "� in thunderstorms, ice crystal charges are similarly acquired by collision processes RATHER THAN BY ANY OTHER MECHANISM". It is puzzling to understand why the authors have chosen to ignore ion attachment, an important ice crystal charging process that does not involve collisions between ice crystals. Beginning with Gish and Wait (1950), numerous investigators have demonstrated that ion currents flow to the tops of thunderclouds as predicted by Wilson (1920). Marshall et al. (1989) and Byrne et al. (1989) have found that ice particles at cloud top carry appreciable charges that appear to be derived from the Wilson current. In an average storm there can be little doubt that this mechanism too could be producing charged ice crystals at the required rate of about a coulomb per second (Vonnegut, 1990).
Vonnegut, B.; Moore, C. B.
Ice-Crystal Fallstreaks from Supercooled Liquid Water Parent Clouds
NASA Technical Reports Server (NTRS)
On 31 December 2001, ice-crystal fallstreaks (e.g., cirrus uncinus, or colloquially "Mare's Tails") from supercooled liquid water parent clouds were observed by ground-based lidars pointed vertically from the Atmospheric Radiation Measurement Southern Great Plains (SGP) facility near Lamont, Oklahoma. The incidence of liquid phase cloud with apparent ice-phase precipitation is investigated. Scenarios for mixed-phase particle nucleation, and fallstreak formation and sustenance are discussed. The observations are unique in the context of the historical reverence given to the commonly observed c h s uncinus fallstreak (wholly ice) versus this seemingly contradictory coincidence of liquid water begetting ice-crystal streaks.
Campbell, James R.; O'C. Starr, David; Welton, Ellsworth J.; Spinhirne, James D.; Ferrare, Richard A.
Diagnosing the Ice Crystal Enhancement Factor in the Tropics
NASA Technical Reports Server (NTRS)
Recent modeling studies have revealed that ice crystal number concentration is one of the dominant factors in the effect of clouds on radiation. Since the ice crystal enhancement factor and ice nuclei concentration determine the concentration, they are both important in quantifying the contribution of increased ice nuclei to global warming. In this study, long-term cloud-resolving model (CRM) simulations are compared with field observations to estimate the ice crystal enhancement factor in tropical and midlatitudinal clouds, respectively. It is found that the factor in tropical clouds is 10 3-104 times larger than that of mid-latitudinal ones, which makes physical sense because entrainment and detrainment in the Tropics are much stronger than in middle latitudes. The effect of entrainment/detrainment on the enhancement factor, especially in tropical clouds, suggests that cloud microphysical parameterizations should be coupled with subgrid turbulence parameterizations within CRMs to obtain a more accurate depiction of cloud-radiative forcing.
Zeng, Xiping; Tao, Wei-Kuo; Matsui, Toshihisa; Xie, Shaocheng; Lang, Stephen; Zhang, Minghua; Starr, David O'C; Li, Xiaowen; Simpson, Joanne
Radar backscattering properties of nonspherical ice crystals at 94 GHz
The millimeter wavelength radar backscattering properties at 94 GHz for six nonspherical ice crystals, which include hexagonal column, hollow, plate, bullet rosette, aggregate, and droxtal with 46 maximum dimensions ranging from 2 to 10,500 mum, are investigated using the discrete dipole approximation (DDA) method and Lorenz-Mie theory. It is found that the radar backscattering cross sections are sensitive to ice
Gang Hong
Radar backscattering properties of nonspherical ice crystals at 94 GHz
The millimeter wavelength radar backscattering properties at 94 GHz for six nonspherical ice crystals, which include hexagonal column, hollow, plate, bullet rosette, aggregate, and droxtal with 46 maximum dimensions ranging from 2 to 10,500 ?m, are investigated using the discrete dipole approximation (DDA) method and Lorenz-Mie theory. It is found that the radar backscattering cross sections are sensitive to ice
Gang Hong
Enhanced and Oriented Riming of Growing Ice Crystals.
NASA Astrophysics Data System (ADS)
Geometrically oriented riming was found in Formvar resin replicas of columnar ice crystals collected in cumulus clouds at -6�C during an aircraft field program in Texas. Rimed cloud droplets were found either on the ends of the crystals or in a girdle around the middle. Oriented riming is attributed to preferential collection on growing ice crystals with charge separations between the crystal body and growing ends. Droplet attraction to separated charge regions of growing ice crystals results in enhanced riming and increases the rate of precipitation development. Effects of this process on cloud electrification depend on whether the cloud droplets carry net charges or are polarized. The impact of this oriented riming process on several cloud electrification scenarios is discussed.
Finnegan, William G.; Chai, Steven K.; Detwiler, Andrew
How big should hexagonal ice crystals be to produce halos?
It has been hypothesized that the frequent lack of halos in observations of cirrus and contrails and laboratory measurements is caused by small ice crystal sizes that put the particles outside the geometrical optics domain of size parameters. We test this hypothesis by exploiting a strong similarity of ray tracing phase functions for finite hexagonal and circular ice cylinders and using T-matrix computations of electromagnetic scattering by circular cylinders with size parameters up to 180 in the visible. We conclude that well-defined halos should be observable for ice crystal size parameters of the order of 100 and larger and discuss remote-sensing implications of this result. PMID:18305781
Mishchenko, M I; Macke, A
Separation of millimeter-wave radar reflectivities of aggregates and pristine ice crystals in a cloud
Millimeter wave radars operating at 35 and 94 GHz are being used for the remote sensing of ice clouds. Two-dimensional particle probe measurements in clouds show that a single type of ice crystals (e.g., column, plate, stellar crystal, etc.) is often observed in a mixture with ice crystal aggregates. This may pose a problem for estimating the ice water content
K. Aydin; T. M. Walsh
Display of ice crystal flutter in atmospheric light pillars
NASA Astrophysics Data System (ADS)
Specular patterns in the atmosphere caused by ice crystals with preferably horizontal orientation are quantitatively described by use of a bidirectional phase function for a fluttering plate. The main qualitative features of the sun pillars and overground light pillars are explained. Possibilities to retrieve the probability density for orientation of the preferably oriented crystals from the specular patterns are discussed.
Borovoi, Anatoli; Kustova, Natalia
Light scattering by single ice crystals of cirrus clouds
NASA Astrophysics Data System (ADS)
In situ measurements of angular scattering intensities (ASIs) related to single ice crystals of cirrus clouds were obtained for the first time with the airborne Polar Nephelometer instrument. These observations were performed in the southern mid-latitudes during the INCA project. The analysis of the data shows that the well marked peaks of the ASIs are undoubtedly attributed to quasi-specular reflections from crystal facets and the refracted rays passed through the ice crystals. Emphasizing that it is not enough to know the shape of the crystal, but also the internal structure is of great importance. Ray tracing simulations reproduce most of the observed ASIs features. The model of surface roughness, which assumes the Weibull statistics, enables to reproduce the quasi-specular external reflection from crystal facets. It follows from the retrievals that the surface of the crystals was deeply rough and the amount of the internal inclusions (air bubbles) was quite high.
Shcherbakov, Valery; Gayet, Jean-Fran�ois; Jourdan, Olivier; Str�m, Johan; Minikin, Andreas
Modeling, simulation, and comparison study of cirrus cloud ice crystals
NASA Astrophysics Data System (ADS)
Various methods and techniques to estimate ice crystals radar response have been developed to study the structure of cirrus clouds. Most methods assume a spherical shape for the ice crystals. This assumption leads to mistakes on the parameter estimation related to the particles' size. In this work, we modeled the shape of ice particles found in cirrus cloud as measured by airborne instruments, specifically ice bullets. These can be found depending on the temperature and cloud altitude, isolated or in groups of two or more bullets, called bullet rosettes. The model of the bullets was developed using the parameters obtained by airborne measurements from the National Center for Atmospheric Research (NCAR) Video Ice Particle Sampler (VIPS). This is an airborne instrument that takes samples of the cirrus cloud particles sizes. With these sample parameters we created a bullet function in DDSCAT with the actual shape of the bullets. This software allows us to create irregular models of particles using the Discrete Dipole Approximation method. With this model we can analyze the backscattering produced by the bullet and rosette model or reflectivity and compute the total volume backscattering coefficient from the cirrus clouds. Various models of ice crystal habits are compared.
Villa, Jorge M.; Cruz-Pol, Sandra L.; Colom-Ustariz, Jose G.; Sekelsky, Stephen M.
Ice crystal properties retrieval using radar spectral polarimetric measurements within ice\\/mixed-phase clouds
In the field of atmospheric research, ground-based radar systems are often employed to study ice\\/mixed-phase cloud properties based on retrieval techniques. These techniques convert the radar signal backscattered by each bulk of ice crystals being probed within the same radar resolution volume to cloud�s microphysical characteristics. However, the size of a radar resolution volume is often too large compared to
Y. Dufournet
Crystallization of amorphous water ice in the solar system.
Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated. PMID:11539415
Jenniskens, P; Blake, D F
Crystallization of amorphous water ice in the solar system
NASA Technical Reports Server (NTRS)
Electron diffraction studies of vapor-deposited water ice have characterized the dynamical structural changes during crystallization that affect volatile retention in cometary materials. Crystallization is found to occur by nucleation of small domains, while leaving a significant part of the amorphous material in a slightly more relaxed amorphous state that coexists metastably with cubic crystalline ice. The onset of the amorphous relaxation is prior to crystallization and coincides with the glass transition. Above the glass transition temperature, the crystallization kinetics are consistent with the amorphous solid becoming a "strong" viscous liquid. The amorphous component can effectively retain volatiles during crystallization if the volatile concentration is approximately 10% or less. For higher initial impurity concentrations, a significant amount of impurities is released during crystallization, probably because the impurities are trapped on the surfaces of micropores. A model for crystallization over long timescales is described that can be applied to a wide range of impure water ices under typical astrophysical conditions if the fragility factor D, which describes the viscosity behavior, can be estimated.
Jenniskens, P.; Blake, D. F.
Ice-binding proteins that accumulate on different ice crystal planes produce distinct thermal hysteresis dynamics.
Ice-binding proteins that aid the survival of freeze-avoiding, cold-adapted organisms by inhibiting the growth of endogenous ice crystals are called antifreeze proteins (AFPs). The binding of AFPs to ice causes a separation between the melting point and the freezing point of the ice crystal (thermal hysteresis, TH). TH produced by hyperactive AFPs is an order of magnitude higher than that produced by a typical fish AFP. The basis for this difference in activity remains unclear. Here, we have compared the time dependence of TH activity for both hyperactive and moderately active AFPs using a custom-made nanolitre osmometer and a novel microfluidics system. We found that the TH activities of hyperactive AFPs were time-dependent, and that the TH activity of a moderate AFP was almost insensitive to time. Fluorescence microscopy measurement revealed that despite their higher TH activity, hyperactive AFPs from two insects (moth and beetle) took far longer to accumulate on the ice surface than did a moderately active fish AFP. An ice-binding protein from a bacterium that functions as an ice adhesin rather than as an antifreeze had intermediate TH properties. Nevertheless, the accumulation of this ice adhesion protein and the two hyperactive AFPs on the basal plane of ice is distinct and extensive, but not detectable for moderately active AFPs. Basal ice plane binding is the distinguishing feature of antifreeze hyperactivity, which is not strictly needed in fish that require only approximately 1�C of TH. Here, we found a correlation between the accumulation kinetics of the hyperactive AFP at the basal plane and the time sensitivity of the measured TH. PMID:25008081
Drori, Ran; Celik, Yeliz; Davies, Peter L; Braslavsky, Ido
The Examination by Electron Microscope of Ice Crystal Nuclei from Cloud Chamber Experiments
A method is described whereby ice crystals generated in a Bigg-Warner ice nuclei counter may be replicated on Formvar coated slides. The Formvar film, with replicas, is subsequently removed for examination in the electron microscope. The nuclei of the ice crystals remain on the Formvar after sublimation of the ice, and under favorable conditions, may be identified by their morphology
John Rucklidge
Statistical approach to light scattering by convex ice crystals.
Within the geometric optics approximation, the phase functions of randomly oriented ice crystals are calculated as a series relative to multiplicity of internal collisions of light inside the particles. In the case of convex crystals, it is shown that the coefficients of the series provide the most information about the crystal shapes, while the angular functions of this series are weakly dependent on the shapes. The prevailing role of the term corresponding to one internal collision is emphasized. Three numbers describing a distribution of the single-collision scattered light among the aureole and halos of 22 degrees and 46 degrees prove to be the basic parameters by which to characterize scattering by hexagonal ice crystals. PMID:16688282
Borovoi, Anatoli; Kustova, Natalia
Effect of the Inhomogeneity of Ice Crystals on Retrieving Ice Cloud Optical Thickness and Effective Particle Size
NASA Technical Reports Server (NTRS)
Spherical or spheroidal air bubbles are generally trapped in the formation of rapidly growing ice crystals. In this study the single-scattering properties of inhomogeneous ice crystals containing air bubbles are investigated. Specifically, a computational model based on an improved geometric-optics method (IGOM) has been developed to simulate the scattering of light by randomly oriented hexagonal ice crystals containing spherical or spheroidal air bubbles. A combination of the ray-tracing technique and the Monte Carlo method is used. The effect of the air bubbles within ice crystals is to smooth the phase functions, diminish the 22deg and 46deg halo peaks, and substantially reduce the backscatter relative to bubble-free particles. These features vary with the number, sizes, locations and shapes of the air bubbles within ice crystals. Moreover, the asymmetry factors of inhomogeneous ice crystals decrease as the volume of air bubbles increases. Cloud reflectance lookup tables were generated at wavelengths 0.65 m and 2.13 m with different air-bubble conditions to examine the impact of the bubbles on retrieving ice cloud optical thickness and effective particle size. The reflectances simulated for inhomogeneous ice crystals are slightly larger than those computed for homogenous ice crystals at a wavelength of 0.65 microns. Thus, the retrieved cloud optical thicknesses are reduced by employing inhomogeneous ice cloud models. At a wavelength of 2.13 microns, including air bubbles in ice cloud models may also increase the reflectance. This effect implies that the retrieved effective particle sizes for inhomogeneous ice crystals are larger than those retrieved for homogeneous ice crystals, particularly, in the case of large air bubbles.
Xie, Yu; Minnis, Patrick; Hu, Yong X.; Kattawar, George W.; Yang, Ping
Ice crystallization in ultrafine water-salt aerosols: nucleation, ice-solution equilibrium, and internal structure.
Atmospheric aerosols have a strong influence on Earth's climate. Elucidating the physical state and internal structure of atmospheric aqueous aerosols is essential to predict their gas and water uptake, and the locus and rate of atmospherically important heterogeneous reactions. Ultrafine aerosols with sizes between 3 and 15 nm have been detected in large numbers in the troposphere and tropopause. Nanoscopic aerosols arising from bubble bursting of natural and artificial seawater have been identified in laboratory and field experiments. The internal structure and phase state of these aerosols, however, cannot yet be determined in experiments. Here we use molecular simulations to investigate the phase behavior and internal structure of liquid, vitrified, and crystallized water-salt ultrafine aerosols with radii from 2.5 to 9.5 nm and with up to 10% moles of ions. We find that both ice crystallization and vitrification of the nanodroplets lead to demixing of pure water from the solutions. Vitrification of aqueous nanodroplets yields nanodomains of pure low-density amorphous ice in coexistence with vitrified solute rich aqueous glass. The melting temperature of ice in the aerosols decreases monotonically with an increase of solute fraction and decrease of radius. The simulations reveal that nucleation of ice occurs homogeneously at the subsurface of the water-salt nanoparticles. Subsequent ice growth yields phase-segregated, internally mixed, aerosols with two phases in equilibrium: a concentrated water-salt amorphous mixture and a spherical cap-like ice nanophase. The surface of the crystallized aerosols is heterogeneous, with ice and solution exposed to the vapor. Free energy calculations indicate that as the concentration of salt in the particles, the advance of the crystallization, or the size of the particles increase, the stability of the spherical cap structure increases with respect to the alternative structure in which a core of ice is fully surrounded by solution. We predict that micrometer-sized particles and nanoparticles have the same equilibrium internal structure. The variation of liquid-vapor surface tension with solute concentration is a key factor in determining whether a solution-embedded ice core or vapor-exposed ice cap is the equilibrium structure of the aerosols. In agreement with experiments, we predict that the structure of mixed-phase HNO3-water particles, representative of polar stratospheric clouds, consists of an ice core surrounded by freeze-concentrated solution. The results of this work are important to determine the phase state and internal structure of sea spray ultrafine aerosols and other mixed-phase particles under atmospherically relevant conditions. PMID:24820354
Hudait, Arpa; Molinero, Valeria
Pattern Formation during Ice Crystal Growth -ISS KIBO Experiments-
NASA Astrophysics Data System (ADS)
Crystal growth experiments of ice in supercooled D2O water were carried out in the Japan Experiment Module KIBO of the International Space Station (ISS) in the period between December 2008 and March 2009. Overview of this project and preliminary results are presented.
Furukawa, Yoshinori; Yokoyama, Etsuro; Yoshizaki, Izumi; Yoda, Shinichi; Tanaka, Tetsuo; Shimaoka, Taro; Sone, Takehiko; Tomobe, Toshiyuki
A Critical Look at Ice Crystal Growth Data
I review published data relating to the growth of ice crystals from water vapor under various conditions, and I critically examine the different measurements to determine what useful information can be extracted from each. I show that most, and possibly all, of the existing growth data have been seriously distorted by systematic errors of one form or another, to varying
Kenneth G. Libbrecht
Ice crystal growth in a dynamic thermal diffusion chamber
NASA Technical Reports Server (NTRS)
Ice crystals were grown in a supersaturated environment produced by a dynamic thermal diffusion chamber, which employed two horizontal plates separated by a distance of 2.5 cm. Air was circulated between and along the 1.2 m length of the plates past ice crystals which nucleated and grew from a fiber suspended vertically between the two plates. A zoom stereo microscope with a magnification which ranged from 3X to 80X and both 35 mm still photographs and 16 mm time lapse cine films taken through the microscope were used to study the variation of the shape and linear growth rate of ice crystals as a function of the ambient temperature, the ambient supersaturation, and the forced ventilation velocity. The ambient growth conditions were varied over the range of temperature 0 to -40 C, over the range of supersaturation 4% to 50% with respect to ice, and over the range of forced ventilation velocities 0 cm/s to 20 cm/s.
Keller, V. W.
Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument
NASA Technical Reports Server (NTRS)
The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring those ice-cloud parameters that included using FSSP-100 and 230-X 1-D optical probes for ice-crystal concentrations, a film-loop microscope for ice-crystal habits and dimensions, and an in-situ microscope for determining ice-crystal orientation. Intercomparisons were made in ice clouds containing ice crystals ranging in size from about 10 microns to 150 microns diameter, and ice crystals with plate, columnar, dendritic, and spherical shapes. It was not possible to determine conclusively that the PVM accurately measures IWC, PSA, and Re of ice crystals, because heat from the PVM evaporated in part the crystals in its vicinity in the chamber thus affecting its measurements. Similarities in the operating principle of the FSSP and PVM, and a comparison between Re measured by both instruments, suggest, however, that the PVM can make those measurements. The resolution limit of the PVM for IWC measurements was found to be on the order of 0.001 g/cubic m. Algorithms for correcting IWC measured by FSSP and PVM were developed.
Gerber, H.; DeMott, P. J.; Rogers, D. C.
Simulation of the quasi-spherical wire-array implosion dynamics based on a multi-element model
NASA Astrophysics Data System (ADS)
The implosion dynamics of quasi-spherical wire arrays with different initial aspect ratios are investigated with a multi-element model, and the simulated results are compared with experimental results in the Qiangguang-1 Facility in 2011. According to the simulation, the pinch plasmas implode in different modes when the aspect ratios of the initial wire arrays are different. The aspect ratio of the wire array in shot 11259 is 0.76, and the simulated pinch plasma implodes onto the equatorial surface. In shot 11268, the aspect ratio is 1.33 and the plasma implodes onto the central axis. In shot 11270, the aspect ratio is 1.05 and the plasma implodes toward the central point of the load. The simulated shapes of the plasma shells are in good accordance with the experimental time-resolved x-ray framing images. The simulated imploding times are consistent with the experimental x-ray peak times. The quasi-spherical implosion is more effective in driving inertial controlled fusion.
Chu, Y. Y.; Li, Z. H.; Yang, J. L.; Ding, N.; Xu, R. K.; Xu, Z. P.; Ye, F.; Zhang, F. Q.; Chen, D. Y.
The alignment of ice crystals in changing electric fields
NASA Astrophysics Data System (ADS)
Orientation of ice crystals in the form of thin plates (diameter up to 30 ?m, thickness 0.5 to a few ?m) was investigated optically for crystals nucleated in a supercooled cloud in a laboratory cold chamber. Random orientation caused by Brownian rotation of small crystals (apparent as twinkling) and alignment caused by airflow resulting from fall motion of larger crystals was changed by application of an electric field either as a step or as an oscillating square wave of variable frequency of order 1-10 Hz. Video records and time exposed still photographs demonstrated crystal fall, oscillation, and orientation changes with electric field magnitude and frequency. Thin film interference colours provided crystal thickness, mass, and moment of inertia. Realignment began for electric fields greater than 0.5-1 kV/m and was complete above 10 kV/m. Measurements of degree of alignment (from random orientation to completely parallel to the electric field) and its time dependence (of order tenths of seconds) are consistent with predictions of a theoretical oscillator model based on electrical torques on ellipsoids in viscous air. In a changing electric field at low frequency, the crystal realignment varies along with the variation field and at high frequency they remain aligned along the average field. These results are applied to larger crystals as occur in the atmosphere with implication for remote sensing of ice by radar and lidar as influenced by local electric fields and with the possibility of their remote measurement by optical observation of changing crystal orientations.
Foster, T. C.; Hallett, J.
The microphysical properties of small ice particles measured during MACPEX
NASA Astrophysics Data System (ADS)
During the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) field campaign, the Small Ice Detector version 3 (SID-3) and the NCAR Video Ice Particle Sampler (VIPS) probes were operated onboard the NASA WB-57 aircraft to measure the microphysical properties of small ice particles in midlatitude cirrus clouds. The VIPS was optimized to measure the particle size distribution and projected area properties of ice particles between 20 and 200 microns and measurements agreed well with other microphysical probes. SID-3 measures the forward light scattering pattern from ice particles in the 1 to 100 micron size range. Forward scattering patterns can be used to characterize ice particle shape as well as surface roughness. Scattering patterns appear to be 'speckled' when particles have surface roughness and/or are polycrystalline. Scattering patterns can be used to identify quasi-spherical ice particles as well as particles which are sublimating. Sublimating crystals, spherical ice particles, and particles with surface roughness were all observed by SID-3 during MACPEX. Observed particle properties will be correlated to concurrent atmospheric observations. Measurements from the controlled environment of the Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber will be related to atmospheric particle measurements.
Schmitt, C. G.; Schnaiter, M.; Heymsfield, A.; Bansemer, A.; Hirst, E.
A Critical Look at Ice Crystal Growth Data
I review published data relating to the growth of ice crystals from water\\u000avapor under various conditions, and I critically examine the different\\u000ameasurements to determine what useful information can be extracted from each. I\\u000ashow that most, and possibly all, of the existing growth data have been\\u000aseriously distorted by systematic errors of one form or another, to varying
Kenneth G. Libbrecht
Study of the implosion characteristics of quasi-spherical wire arrays on the Angara-5-1 facility at currents of up to 4 MA
Results are presented from experimental studies of the spatial distribution of the density of matter in the central part of the discharge gap and the formation of the temporal profile of the X-ray power in the course of implosion of quasi-spherical wire arrays at discharge currents of up to 4 MA. The spatial distribution of the X-ray intensity in the central part of the discharge gap and the temporal profile of the X-ray power are used as implosion characteristics of quasi-spherical wire arrays. The quasi-spherical arrays were formed by the radial stretching of unstrained wires of initially cylindrical and conical wire arrays under the action of the electrostatic field. The temporal profile of the output X-ray pulse in the photon energy range of 0.1-1 keV is shown to depend on both the geometrical parameters of the quasi-spherical array and the longitudinal distribution of its mass. It is found that a 40% increase in the wire mass due to deposition of an additional mass in the equatorial region of a quasi-spherical array leads to a 15% increase in the average current radius of the pinch and a 30% decrease in the X-ray yield. Experiments with quasi-spherical arrays made of kapron fibers with deposited Al and Bi conducting layers were also carried out. It is demonstrated that application of such arrays makes it possible to control the profile and duration of the generated X-ray pulse by varying the mass, material, and location of the deposited layer. It is found that deposition of an additional mass in the form of a thin Bi stripe on tungsten wires near the cathode end of the array allows one to mitigate the influence of the cathode zipper effect on the pinch compression and formation of the X-ray pulse in tungsten arrays.
Aleksandrov, V. V.; Volkov, G. S.; Grabovski, E. V.; Gribov, A. N.; Gritsuk, A. N.; Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Sasorov, P. V.; Frolov, I. N. [Troitsk Institute for Innovation and Fusion Research (Russian Federation)
Study of the implosion characteristics of quasi-spherical wire arrays on the Angara-5-1 facility at currents of up to 4 MA
NASA Astrophysics Data System (ADS)
Results are presented from experimental studies of the spatial distribution of the density of matter in the central part of the discharge gap and the formation of the temporal profile of the X-ray power in the course of implosion of quasi-spherical wire arrays at discharge currents of up to 4 MA. The spatial distribution of the X-ray intensity in the central part of the discharge gap and the temporal profile of the X-ray power are used as implosion characteristics of quasi-spherical wire arrays. The quasi-spherical arrays were formed by the radial stretching of unstrained wires of initially cylindrical and conical wire arrays under the action of the electrostatic field. The temporal profile of the output X-ray pulse in the photon energy range of 0.1-1 keV is shown to depend on both the geometrical parameters of the quasi-spherical array and the longitudinal distribution of its mass. It is found that a 40% increase in the wire mass due to deposition of an additional mass in the equatorial region of a quasi-spherical array leads to a 15% increase in the average current radius of the pinch and a 30% decrease in the X-ray yield. Experiments with quasi-spherical arrays made of kapron fibers with deposited Al and Bi conducting layers were also carried out. It is demonstrated that application of such arrays makes it possible to control the profile and duration of the generated X-ray pulse by varying the mass, material, and location of the deposited layer. It is found that deposition of an additional mass in the form of a thin Bi stripe on tungsten wires near the cathode end of the array allows one to mitigate the influence of the cathode zipper effect on the pinch compression and formation of the X-ray pulse in tungsten arrays.
Aleksandrov, V. V.; Volkov, G. S.; Grabovski, E. V.; Gribov, A. N.; Gritsuk, A. N.; Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Sasorov, P. V.; Frolov, I. N.
Nanoscale Ice: Spectroscopic Ellipsometry of Epitaxially-Grown Crystals
NASA Astrophysics Data System (ADS)
A new laboratory technique has been developed to examine the surface characteristics and kinetics of ice crystals at the nanoscale. Uncertainties remain regarding the fundamental physics of nucleation and depositional growth in atmospheric ice crystals. These molecular-scale uncertainties propagate upward into modeling outcomes at all scales of atmospheric interest: particle models, cloud models, mesoscale models, and climate models. Molecular-scale growth mechanisms and kinetics have been mainly inferred from bulk and particle-scale experiments as well as crystal-growth theory. The precarious nature of the ice surface resisted the first generation of direct nanoscale probing technologies, but new in-situ techniques including ESEM, AFM, and ellipsometry promise to divulge a wealth of new knowledge. Spectroscopic ellipsometry measures changes in the polarization state of light as it reflects off the surface of a thin film. This non-destructive technique is capable of measuring layer thicknesses as small as a single monolayer (~1 �) and up to thicknesses of ~10 ?m. Other physical parameters including index of refraction and surface roughness are also accessible. At the TCNJ Cloud Physics Laboratory, a Horiba Scientific Auto-SE ellipsometer (440 - 1000 nm spectral range) has been adapted for in-situ measurements of ice crystals. The ice crystals are grown epitaxially on various horizontal substrates in a custom-built static diffusion chamber. The diffusion chamber is housed within a vacuum chamber and an optical path is provided from the ellipsometer light source to sample stage and back to the ellipsometer analyzer at 75� from normal. The diffusion chamber is cooled in two stages, with initial cooling accomplished with a fluid-chilled block and final chilling controlled by two independent thermoelectric cells. A wide range of temperatures, pressures, and saturation ratios are accessible: from 0�C to -30�C, 50mb to atmospheric pressure, and from subsaturated to greater that 200% RHi. Temperature and moisture profiles are continuously determined by platinum resistance thermometers. Optimization of cooling efficiencies are under way and should permit extension of temperature range to -60�C. Ongoing efforts are targeted at kinetic measurements of thickness changes in order to identify growth thresholds as a function of ambient conditions and nucleation mechanism.
Cumiskey, A.; Grippaldi, J.; Magee, N. B.
Crystal Ice Formation of Solution and Its Removal Phenomena on a Vertical Cooled Plate
NASA Astrophysics Data System (ADS)
Experimental and analytical studies for freezing phenomena of ethylene glycol solution on a vertical cooled polyvinyl-chloride plate have been performed. It is found that the crystal ice formed on the vertical plate is removed from the plate surface due to buoyancy force acting on the crystal ice. It is shown that the crystal ice formed on the vertical plate slides along the plate surface due to buoyancy force and the crystal ice grows in a shape of sheet by joining with the neighbour ice. The number of the removed ice per unit of time is, therefore, decreased as compared to that for the horizontal plate. It is found that the onset of ice removal condition is related to the heat fluxes from the plate surface to the plate and from the plate surface to the solution. The ice removal occurs easily for a vertical plate than for a horizontal one.
Hirata, Tetsuo; Ishikawa, Masaaki; Matsuzaki, You
An uncoupled multiphase approach towards modeling ice crystals in jet engines
NASA Astrophysics Data System (ADS)
A recent series of high altitude turbofan engine malfunctions, characterized by flameout and sudden power losses have been reported in recent years. The source of these incidents has been hypothesized to be due to the presence of ice crystals at high altitudes. Ice crystals have been shown to have ballistic trajectories and consequently enter the core engine flow, without getting centrifuged out towards the engine bypass as droplets do. The crystals may melt as they move downstream to higher temperatures in successive stages, or hit a heated surface. The wetted surface may then act as an interface for further crystal impingement, which locally reduces the temperature and could lead to an ice accretion on the components. Ice can accrete to dangerously high levels, causing compressor surge due to blockage of the primary flowpath, vibrational instabilities due to load imbalances of ice on rotating components, mechanical damage of components downstream due to large shed ice fragments, or performance losses if ice enters the combustor, causing a decreased burner efficiency and an eventual flame-out. In order to provide a numerical tool to analyze such situations, FENSAP-ICE has been extended to model mixed-phase flows that combine air, water and ice crystals, and the related ice accretion. DROP3D has been generalized to calculate particle impingement, concentration, and field velocities in an uncoupled approach that neglects any phase change by assuming both ice crystals and supercooled droplets are in thermodynamic equilibrium. ICE3D then accounts for the contribution of ice crystals that stick and melt on an existing water-film and promote ice accretion. The extended ice crystal impingement and ice accretion model has been validated against test data from Cox and Co. and National Research Council icing tests conducted on a NACA0012 airfoil and unheated non-rotating cylinder respectively. The tests show a consistent agreement with respect to experimental profiles in terms of capturing the overall shape, although some of the ice profiles were conservative since they over-predicted the amount of ice accreted. The experimental observations suggest that ice crystals cause splashing of an existing film, and erosion effects when they impact an iced surface, and cause an overall loss in the amount of ice, as well as a general streamlining of the ice profile. This has not been taken into account in the present numerical model. The overall predictions in comparison with other numerical models, however, have improved and are a promising step towards simulating ice-shedding characteristics in a turbomachine.
Nilamdeen, Mohamed Shezad
Optical detection and characterization of ice crystals in LACIS
NASA Astrophysics Data System (ADS)
Tropospheric ice and mixed phase clouds are an integral part of the earth system and their microphysical and radiative properties are strongly coupled e.g. through the complexities of the ice nucleation process. Therefore the investigation of influences of different aerosol particles which act as ice nuclei (IN) on the freezing behaviour of cloud droplets is important and still poses unresolved questions. The Leipzig Aerosol and Cloud Interaction Simulator (LACIS) is used to investigate the IN activity of different natural and artificial aerosol particles (mineral dust, soot etc.) in heterogeneous freezing processes (immersion or deposition freezing). A critical part of LACIS is the particle detection system allowing for size-resolved counting of activated seed particles and discrimination between ice crystals and water droplets. Recently, two instruments have been developed to provide these measurements at the LACIS facility. The Thermally-stabilized Optical Particle Spectrometer (TOPS) is measuring the particle size based on the intensity of light scattered by individual particles into a near-forward (15� to 45�) direction. Two symmetrical forward scattering channels allow for optical determination of the sensing volume, thus reducing the coincidence counting error and the edge zone effect. The backscatter channel (162� to 176�) equipped with a rotatable cross polarizer allows for establishing the change in linear polarization state of the scattered light. The backscatter elevation angle is limited so that the linear depolarization of light scattered by spherical particles of arbitrary size is zero. Any detectable signal in the depolarization channel can be therefore attributed to non-spherical particles (ice crystals). With consideration of the signal in the backscatter channel the separate counting of water drops and ice particle is possible. The Leipzig Ice Scattering Apparatus (LISA) is a modified version of the Small Ice Detector (SID3), developed at the Science and Technology Research Institute at the University of Hertfordshire, UK. The SID instruments have been developed primarily as wing-mounted systems for airborne studies of cloud ice particles. SID3 records the forward scattered light pattern with high angular resolution using an intensified CCD (780 by 582 pixels) at a rate of 20 images per second. In addition to the SID3 capabilities, LISA is able to measure the circular depolarization ratio in the range of scattering angles from 166� to 172�. Whereas particle size, shape and orientation are characterized by the angular distribution of forward-scattered light, the measured value of the circular depolarization can be used to validate the existing theoretical models of light scattering by irregular particles (RTDF, GSVM, T-Matrix, DDA). The first measurements done at the LACIS facility have demonstrated a promising sensitivity of LISA's depolarization channel to the shape of ice crystals. Results showed an increase of the mean circular depolarization ratio from 1.5 (characteristic for the liquid water droplets above 3 �m) to 2.5 for the "just frozen" almost-spherical droplets in the same size range. The presentation will describe details of instruments set up and present some exemplary results from experiments carried out at LACIS and AIDA (KIT) facilities.
Kiselev, Alexei; Clau�, Tina; Niedermeier, Dennis; Hartmann, Susan; Wex, Heike; Stratmann, Frank
The Influence of Radiation on Ice Crystal Spectrum in the Upper Troposphere
NASA Technical Reports Server (NTRS)
This theoretical study is carried out to investigate the effect of radiation on ice crystal spectrum in the upper troposphere. First, an explicit expression is obtained for the ice crystal growth rate that takes account of radiative and kinetic effects. Second, the expression is used to quantitatively analyze how radiation broadens the ice crystal spectrum and then reveal a new precipitation mechanism in the upper troposphere and the stratosphere. Third, the radiative effect is used to explain the subvisual clouds near the tropopause.
Zeng, Xiping
Ice crystal growth in water vapor at high saturation
NASA Technical Reports Server (NTRS)
A simple technique is presented for estimating the energy of formation of monolayer icelike clusters at ice-vapor interfaces. Under the assumptions that the ice surfaces are smooth and sparsely covered with monomers, dimers, etc., in near equilibrium with the vapor, and that the bond energies and configurational entropy dominate the energy of formation, it is found that the basal surfaces prefer triangular embryos with an orientation which reverses from layer to layer, whereas the most stable clusters on the prism surfaces are rectangular in configuration. The preferred prism clusters are determined to have a significantly lower critical energy of formation than the basal clusters due to differences in both corner free energy and configurational entropy. This phenomenon provides a mechanism for strongly anisotropic crystal growth at high saturations.
Bartley, D. L.
Crystal Ice Formation of Solution and Its Removal Phenomena From Cooled Solid Surface
NASA Astrophysics Data System (ADS)
Experimental studies for freezing phenomena of ethylene glycol solution on cooled plate have been performed. A polyvinyl chloride as well as an acrylic resin plates are used for the cooled plates. It is found that the crystal ice formed at the cooled plate is removed from the plate due to buoyancy force acting the crystal ice. It means that ice formation on a cooled plate without deposit ice layer is possible by the present method. It is shown that the cooled plate surface is under cooled about 1.0~1.5 degree below the freezing temperature of the solution during the crystal ice formation and its removal phenomena. The degree of under cooled temperature is unaffected by the cooling temperature of the plate. For higher concentration of solution, it is found that the number of the removed crystal ice per unit time is increased and the volume of each removed ice is decreased.
Hirata, Tetsuo; Ishikawa, Masaaki; Nagasaka, Kouji
Small, Highly Reflective Ice Crystals in Low-Latitude Cirrus
NASA Technical Reports Server (NTRS)
At low latitudes, cirrus are ubiquitous and can be in excess of 100 C colder than the surface, limiting the amount of sunlight absorbed by the earth s atmosphere and surface, and reducing its loss of heat. Here we present aircraft measurements within cirrus over southern Florida indicating that ice crystals have smaller sizes and are more reflective than is assumed in most current climate models. If the measurements are generally representative of low-latitude cirrus, they point to a first-order correction to represenntions of how these clouds affect the earth's climate.
Garrett, T. J.; Gerber, H.; Baumgardner, D. G.; Twohy, C. H.; Weinstock, E. M.
Backscattering by hexagonal ice crystals of cirrus clouds.
Light backscattering by randomly oriented hexagonal ice crystals of cirrus clouds is considered within the framework of the physical-optics approximation. The fine angular structure of all elements of the Mueller matrix in the vicinity of the exact backward direction is first calculated and discussed. In particular, an approximate equation for the differential scattering cross section is obtained. Its simple spectral dependence is discussed. Also, a hollow of the linear depolarization ratio around the exact backward direction inherent to the long hexagonal columns is revealed. PMID:23903169
Borovoi, Anatoli; Konoshonkin, Alexander; Kustova, Natalia
Evolution of ice crystal regions on the microscale based on in situ observations
NASA Astrophysics Data System (ADS)
properties of cirrus clouds largely influence their atmospheric radiative forcing. However, uncertainties remain in simulating/parameterizing the evolution of ice crystals. These uncertainties require more analyses in the Lagrangian view, yet most in situ observations are in the Eulerian view. Here we demonstrate a new method to separate out five phases of ice crystal evolution, using the horizontal spatial relationships between ice supersaturated regions (ISSRs) and ice crystal regions (ICRs). Based on global in situ data sets, we show that the samples of clear-sky ISSRs, ice crystal formation/growth, and evaporation/sedimentation are ~20%, 10%, and 70% of the total ISSR + ICR samples, respectively. In addition, the variance of number-weighted mean diameter (Dc) becomes narrower during the evolution, while the distribution of ice crystal number density (Nc) becomes wider. The new method helps to understand the evolution of ICRs and ISSRs on the microscale by using in situ Eulerian observations.
Diao, Minghui; Zondlo, Mark A.; Heymsfield, Andrew J.; Beaton, Stuart P.; Rogers, David C.
Determination of Ice Crystal Growth Parameters in a Supercooled Cloud Tunnel.
National Technical Information Service (NTIS)
In order to completely understand the behavior of a dynamically changing ice crystal as it falls through a supercooled cloud, the simultaneous determination of the crystal size, mass, apparent density, and fall velocity is desirable. Based on the experien...
M. W. Kowa
Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth
NASA Astrophysics Data System (ADS)
Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C 6H 6), toluene (methylbenzene, C 7H 8), the C 8H 10 isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C 9H 12 isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C 10H 14 compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3-20.8 ?g m -3. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS). Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m -3, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3�10 -3 g s -1 m -2 and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher. Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g ice-1 (toluene, ethylbenzene, xylenes) and 125 pg g ice-1 (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g ice-1 at gas concentrations of 10.3-10.7 ?g m -3 calculated at 295 K. Uptake coefficients ( K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (? G) were between -4.5 and 2.4 kJ mol -1 and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (? H) could be determined between -70.6 and -33.9 kJ mol -1. The uptake entropy (? S) was between -281.3 and -126.8 J mol -1 K -1. Values of ? H and ? S were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.
Fries, Elke; Starokozhev, Elena; Haunold, Werner; Jaeschke, Wolfgang; Mitra, Subir K.; Borrmann, Stephan; Schmidt, Martin U.
Bioprospecting for microbial products that affect ice crystal formation and growth
At low temperatures, some organisms produce proteins that affect ice nucleation, ice crystal structure, and\\/or the process\\u000a of recrystallization. Based on their ice-interacting properties, these proteins provide an advantage to species that commonly\\u000a experience the phase change from water to ice or rarely experience temperatures above the melting point. Substances that bind,\\u000a inhibit or enhance, and control the size, shape,
Brent C. Christner
75 FR 8116 - Notice Pursuant to the National Cooperative Research and Production Act of 1993-Ice Crystal...
Federal Register 2010, 2011, 2012, 2013
...National Cooperative Research and Production Act of 1993--Ice Crystal Consortium Notice is hereby given that, on December 31, 2009...15 U.S.C. 4301 et seq. (``the Act''), the Ice Crystal Consortium (``ICC'') has filed written...
Microfluidic experiments reveal that antifreeze proteins bound to ice crystals suffice to prevent their growth
Antifreeze proteins (AFPs) are a subset of ice-binding proteins that control ice crystal growth. They have potential for the cryopreservation of cells, tissues, and organs, as well as for production and storage of food and protection of crops from frost. However, the detailed mechanism of action of AFPs is still unclear. Specifically, there is controversy regarding reversibility of binding of AFPs to crystal surfaces. The experimentally observed dependence of activity of AFPs on their concentration in solution appears to indicate that the binding is reversible. Here, by a series of experiments in temperature-controlled microfluidic devices, where the medium surrounding ice crystals can be exchanged, we show that the binding of hyperactive Tenebrio molitor AFP to ice crystals is practically irreversible and that surface-bound AFPs are sufficient to inhibit ice crystal growth even in solutions depleted of AFPs. These findings rule out theories of AFP activity relying on the presence of unbound protein molecules.
Celik, Yeliz; Drori, Ran; Pertaya-Braun, Natalya; Altan, Aysun; Barton, Tyler; Bar-Dolev, Maya; Groisman, Alex; Davies, Peter L.; Braslavsky, Ido
Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere.
Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths. PMID:18195749
Fitch, B W; Coulson, K L
Effects on skylight at South Pole Station, Antarctica, by ice crystal precipitation in the atmosphere
NASA Technical Reports Server (NTRS)
Measurements of the radiance and polarization of the skylight at South Pole Station, Antarctica, were made for clear cloud-free skies and cloudless skies with ice crystal precipitation. The measurements were made at six narrowband wavelengths from 321 to 872 nm in the principal plane. The data show that scattering by ice crystals increases the radiance in the backscatter plane, decreases it in the solar plane, and shifts the radiance minimum to a point closer to the sun. The crystals decrease the maximum value of linear polarization and shift the position of the maximum away from the sun. The influence of ice crystal scattering is greatest at the longer wavelengths.
Fitch, B. W.; Coulson, K. L.
Crystal Ice Formation of Solution and Its Removal Phenomena around Vertical Cooled Cylinder
NASA Astrophysics Data System (ADS)
Experimental and analytical studies for freezing phenomena of ethylene glycol solution around a vertical cooled polyvinyl-chloride cylinder have been performed. It is found that the crystal ice formed around the vertical cylinder is removed from the cylinder surface due to buoyancy force acting on the crystal ice. The crystal ice slides along the cylinder surface due to buoyancy force and grows in a shape of tube by joining with the neighbour ice. It is shown that the onset of ice removal condition is related to the heat flux at the cylinder surface when the latent heat of fusion is discharged with freezing, and that the heat flux ratio of 'from the cylinder surface into the cylinder' to 'from the cylinder surface to the solution' is an important parameter for the onset conditions. The ice removal occurs easily for short cylinders than for long ones.
Hirata, Tetsuo; Ishikawa, Masaaki; Akutsu, Nobuaki
New metastable form of ice and its role in the homogeneous crystallization of water.
The homogeneous crystallization of water at low temperature is believed to occur through the direct nucleation of cubic (Ic) and hexagonal (Ih) ices. Here, we provide evidence from molecular simulations that the nucleation of ice proceeds through the formation of a new metastable phase, which we name Ice�0. We find that Ice�0 is structurally similar to the supercooled liquid, and that on growth it gradually converts into a stacking of Ice Ic and Ih. We suggest that this mechanism provides a thermodynamic explanation for the location and pressure dependence of the homogeneous nucleation temperature, and that Ice�0 controls the homogeneous nucleation of low-pressure ices, acting as a precursor to crystallization in accordance with Ostwald's step rule of phases. Our findings show that metastable crystalline phases of water may play roles that have been largely overlooked. PMID:24836734
Russo, John; Romano, Flavio; Tanaka, Hajime
Microscopic pattern of ice crystal growth in the presence of thermal hysteresis proteins
This study examines the effect of thermal hysteresis proteins (THPs) from the winter flounder (Psuedopleuronectes americanus) on the ice-water interface morphology during freezing of aqueous solutions. Experiments were performed using a directional solidification stage, and the development of the two-phase interface was observed through a microscope and recorded by a video system. Unusual ice crystal morphologies were observed, including faceted ice crystal growth along the (1100) crystal plane; spicular or needlelike growth in the (1010) direction; and growth parallel to the c-axis, (0001), consisting of incorporated liquid inclusions bounded by hexagonal prism faces. The observed crystallographic structures can be explained as an effect of the interaction between the THPs and the primary prism faces of ice crystals. This results in an increase in the Gibbs free energy of these planes, followed by ice growth into the supercooled liquid adjacent to these faces.
Coger, R.; Rubinsky, B. (Univ. of California, Berkeley, CA (United States). Dept. of Mechanical Engineering); Fletcher, G. (Memorial Univ. of Newfoundland, St. John's, Newfoundland (Canada))
Direct Visualization of Spruce Budworm Antifreeze Protein Interacting with Ice Crystals: Basal Plane Affinity Confers Hyperactivity
Antifreeze proteins (AFPs) protect certain organisms from freezing by adhering to ice crystals, thereby preventing their growth. All AFPs depress the nonequilibrium freezing temperature below the melting point; however AFPs from overwintering insects, such as the spruce budworm (sbw) are 10�100 times more effective than most fish AFPs. It has been proposed that the exceptional activity of these AFPs depends on their ability to prevent ice growth at the basal plane. To test the hypothesis that the hyperactivity of sbwAFP results from direct affinity to the basal plane, we fluorescently tagged sbwAFP and visualized it on the surface of ice crystals using fluorescence microscopy. SbwAFP accumulated at the six prism plane corners and the two basal planes of hexagonal ice crystals. In contrast, fluorescently tagged fish type III AFP did not adhere to the basal planes of a single-crystal ice hemisphere. When ice crystals were grown in the presence of a mixture of type III AFP and sbwAFP, a hybrid crystal shape was produced with sbwAFP bound to the basal planes of truncated bipyramidal crystals. These observations are consistent with the blockage of c-axial growth of ice as a result of direct interaction of sbwAFP with the basal planes.
Pertaya, Natalya; Marshall, Christopher B.; Celik, Yeliz; Davies, Peter L.; Braslavsky, Ido
Preferred Ice Crystal Orientation Fabric Measurements within the Greenland Ice Sheet Using Multi-Polarization Radar Data
NASA Astrophysics Data System (ADS)
Discharge of ice from the Greenland Ice Sheet to the ocean has increased significantly over the last 25 years due to the acceleration of important outlet glaciers. It was reported that the Greenland Ice Sheet contributed about 2.5 m out of about 6 m of sea-level rise during the Eemian interglacial period. The temperatures during Eemian were reported to be about 8o�4o C higher than the mean of the past millennium. Laboratory measurements have shown that glacial ice, characterized by preferred crystal orientation fabric (COF), is three times more deformable than ice with randomly oriented crystalline structures. Layers characterized by preferred ice COF can influence the flow behavior of a glacier or ice sheet. However, COF measurements are typically obtained from ice cores, and thus are very spatially limited and mostly constrained to areas with little ice flow. A more efficient technique to map the extent of ice fabric over larger regions of ice sheets is needed to better understand the effects on large scale ice flow processes. Radar measurements are capable of discriminating between reflections caused by changes in density, electrical permittivity and COF by exploiting the anisotropic and birefringent properties of ice crystals. For this investigation two radar datasets were collected during the survey of the Greenland Eemian Ice Drilling Site (77.45�N 51.06�W) in August 2008, using a ground-based and chirped-pulse Multi-Channel Radar Depth Sounder (MCRDS) developed by the Center for Remote Sensing of Ice Sheets (CReSIS). The radar used two transmit and eight receive antennas at the center frequency of 150 MHz with a bandwidth of 30 MHz. The first data set consisted of polarimatric measurements acquired in a circular pattern (radius: 35 m) with two co-polarized antenna orientations (one transmitter and four receivers oriented with 90� offsets in the directions of the incident H-Field and E-Field, respectively). Analysis of the circular data shows a periodic power variation with four distinct extinction patterns occurring at 90 degree intervals starting at approximately 700 m depth. Furthermore a 20 degree phase change is observed between the E- and H-field data. Both observations suggest that approximately 72% of the 2542m ice column exhibits birefringent anisotropy caused by preferred ice crystal orientation. The second dataset was acquired in a grid pattern consisting of twenty 10-Km 2D lines (NW to SE) spaced at 0.5-Km and three 10-Km lines (NE to SW) spaced at 2.5-Km. Both transmit and eight receive antenna were oriented parallel to the vehicle track, resulting in E-Field co-polarized data. We will determine the dominant COF relative to the ice divide for a 100 square Km region around the NEEM camp using the results from both datasets. The results of this investigation will be compared to the NEEM ice core observations to determine the accuracy of the analysis. In this investigation we will provide a brief overview of the system and experiments and present the results of data analysis.
Velez-Gonzalez, J. A.; JiLu, L.; Leuschen, C.; Gogineni, P.; Van der Veen, C. J.; Tsoflias, G. P.; Drews, R.; Harish, A. R.
Stability relationship for water droplet crystallization with the NASA Lewis icing spray nozzle
NASA Technical Reports Server (NTRS)
In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.
Marek, C. John; Bartlett, C. Scott
Stability relationship for water droplet crystallization with the NASA Lewis icing spray
NASA Technical Reports Server (NTRS)
In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160 C which results in ice crystals forming in the cloud. To avoid such low temperatures, it is necessary to heat the air and water to high initial temperatures. An icing spray research program was conducted to map the temperatures below which ice crystals form. A soot slide technique was used to determine the presence of crystals in the spray.
Marek, C. John; Bartlett, C. Scott
Ground Based Retrievals of Small Ice Crystals and Water Phase in Arctic Cirrus
NASA Astrophysics Data System (ADS)
The microphysical properties of cirrus clouds are uncertain due to the problem of ice particles shattering at the probe inlet upon sampling. To facilitate better estimation of small ice crystal concentrations in cirrus clouds, a new ground-based remote sensing technique has been used in combination with in situ aircraft measurements. Data from the Mixed-Phase Arctic Cloud Experiment (M-PACE), conducted at the north slope of Alaska (winter 2004), have been used to test a new method for retrieving the liquid water path (LWP) and ice water path (IWP) in mixed phase clouds. The framework of the retrieval algorithm consists of the modified anomalous diffraction approximation or MADA (for mixed phase cloud optical properties), a radar reflectivity-ice microphysics relationship and a temperature-dependent ice particle size distribution (PSD) scheme. Cloud thermal emission measurements made by the ground-based Atmospheric Emitted Radiance Interferometer (AERI) yield information on the total water path (TWP) while reflectivity measurements from the Millimeter Cloud Radar (MMCR) are used to derive the IWP. The AERI is also used to indicate the concentration of small ice crystals (D<50 ?m) relative to the larger ice particles. Combining this small crystal information with the PSD scheme describing the larger particle concentrations yields the retrieved PSD. Small ice crystals are evaluated using the absorption properties of photon tunneling or wave resonance while the liquid water fraction is evaluated using classical Beer's law absorption. While this is still a work in progress, the anticipated products from this AERI-radar retrieval scheme are the IWP, LWP, small-to-large ice crystal number concentration ratio and effective diameter for cirrus, as well as the ice particle number concentration for a given ice water content (IWC).
Mishra, Subhashree; Mitchell, David L.; Deslover, Daniel
A study of the relationship between thunderstorm processes and cloud-top ice crystal size
NASA Astrophysics Data System (ADS)
Satellite observations and numerical models are used to understand the physical mechanisms responsible for thunderstorms with varying cloud-top ice crystal sizes. Geostationary Operational Environmental Satellite (GOES) data are used to create a three-year climatology of cloud-top 3.9 mum reflectivity, a quantity which is closely correlated with particle size. Maximum mean values are found over the High Plains and Rocky Mountain regions of the U.S., suggesting that convection over that region tends to generate smaller anvil ice crystals than areas throughout much of the eastern U.S. To correct for preferred forward scattering by the cloud-top ice crystals, an effective radius retrieval using GOES is developed. Forward radiative transfer simulations are run for a wide range of cloud-top ice crystal sizes and sun-cloud-satellite scattering angles. The output is used to generate a lookup table, so that GOES-measured radiances may be used along with sun-satellite geometry to obtain an estimate for particle size. Validation of the retrieval shows that the assumed scattering properties perform quite well. To help explain the geographical variation in cloud-top ice crystal size, a composite analysis is performed in the High Plains region by averaging environmental conditions for days which produced both small and large ice crystal storms. Small ice is found to occur with relatively high based storms and steep mid-level lapse rates. Additionally, observational evidence from a pyrocumulonimbus event is presented to show the effect of low-level cloud condensation nuclei (CCN) on cloud-top ice crystal size. Model simulations using the Colorado State University Regional Atmospheric Modeling System (RAMS) are performed to help understand the physical mechanisms responsible for cloud-top ice crystal size. Through a series of sensitivity tests, it is found that larger low-level CCN concentrations lead to smaller anvil ice. In addition, as cloud-base temperature decreases (and cloud-base height increases), storm-top ice crystals get smaller. A weaker updraft strength is found to have very little effect on ice crystal size.
Lindsey, Daniel T.
Strain history of ice shells of the Galilean satellites from radar detection of crystal orientation fabric
Orbital radar sounding has been suggested as a means of determining the subsurface thermal and physical structure of the outer ice I shells of the Galilean satellites. At radar frequencies, the dielectric permittivity of single- and polycrystalline water ice I is anisotropic. Crystal orientation fabric (COF), which is indicative of strain history, can be unambiguously detected by comparing the received
Amy C. Barr; David E. Stillman
Ultrasonic Velocity Investigations of Crystal Anisotropy in Deep Ice Cores from Antarctica.
National Technical Information Service (NTIS)
Ice cores from Byrd Station and Little America V have been used to test an ultrasonic technique for evaluating crystal anisotropy in the Antarctic Ice Sheet. P-wave velocities measured parallel and perpendicular to the vertical axes of cores from the 2164...
H. Kohnen A. J. Gow
An Experimental Study of the Production of Ice Crystals by a Twin-Turboprop Aircraft
The University of Wyoming King Air (KA) research aircraft was used in controlled, in situ experiments to determine whether or not, and under what cloud and aircraft operating conditions, a twin-turboprop aircraft would itself produce ice crystals during passage through clouds containing supercooled liquid water. Such crystals are termed `Aircraft Produced Ice Particles' (APIPs). Computer-aided, air-relative navigation was used to
Robert D. Kelly; Gabor Vali
Development of Measurement System for Three-Dimensional Structure of Ice Crystals in Raw Beef Samples
NASA Astrophysics Data System (ADS)
Micro-Slicer Image Processing System (MSIPS) has been developed for measuring the three-dimensional(3-D) structure and distribution of ice crystals formed in biological materials. The system has functions to reconstruct the 3-D image based on the image data of exposed cross sections obtained by multi-slicing of a frozen sample with the minimum thickness of 1?m and to display the internal structure as well as an arbitrary cross section of the sample choosing observation angles. The effects of freezing conditions on the morphology and distribl1tion of ice crystals were demonstrated quantitatively from the observations of raw beef stained by fluorescent indicator. The 3-D image of the sample demonstrated that the growth of ice columns was restricted by the intrinsic structure of muscle fibers. The proposed method provided a new tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.
Do, Gab-Soo; Sagara, Yasuyuki; Tabata, Mizuho; Kudoh, Ken-Ichi; Higuchi, Toshiro
Three-Dimensional Visualization of Ice Crystals in Frozen Materials by Near-Infrared Imaging Spectroscopy
NASA Astrophysics Data System (ADS)
Micro Slicer Spectral Imaging System (MSSIS) has been applied to observe the three-dimensional(3-D) structure and distribution of ice crystals formed in biological materials. MSSIS is composed of a micro-slicer, near-infrared (NIR) illuminator and spectral imaging system. NIR Spectroscopic analysis using MSSIS confirmed that there are a water absorption band around 965 nm and an ice absorption band around 1025 nm. Spectroscopic images of a frozen agar gel and a piece of raw beef at 1,025 nm were obtained by the MSSIS. These images showed the ice crystals could be clearly distinguished from the other components by the different absorbance. The average area of ice crystals was 6,253 ?m2, and the average distances of major and minor axis were 111?m and 62?m respectively. In addition, the 3-D re-constructed image of the ice crystal morphology revealed that they were formed along with the direction of heat transfer. The proposed method provided a novel tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.
Do, Gab-Soo; Ueno, Shigeaki; Sagara, Yasuyuki; Tsuta, Mizuki; Sugiyama, Junichi
Experimental investigation of the interactions of hyperactive antifreeze proteins with ice crystals
NASA Astrophysics Data System (ADS)
Antifreeze proteins (AFPs) evolved in cold-adapted organisms and serve to protect them against freezing cold conditions by arresting ice crystal growth and inhibiting ice recrystallization. The freezing point depression by AFPs is defined as thermal hysteresis (TH) and AFPs are classified as hyperactive (hypAFPs) and moderate according to their TH activities. The mechanism of action of AFPs is not well understood. In particular, it is not clear what determines the concentration dependence of TH and whether the binding of AFP to ice is irreversible. Additionally, it is not known why some types of AFP are hyperactive compared to others and it was suggested that hyperactivity might be related to basal plane affinity of hypAFP to ice. The present study utilizes the techniques of microfluidic devices and fluorescence microscopy to study the interaction of AFPs with ice crystals. With novel temperature controlled microfluidic devices, we showed the accumulation and affinity of hypAFPs on the basal plane of ice. This supports the view that hypAFPs adhere to the basal plane. Additionally, for the first time in literature, small ice crystals of 30-50 mum sizes covered with adsorbed GFP tagged hypAFPs were stabilized in supercooled non-AFP solutions for hours with no observed ice growth in temperature controlled microfluidic devices. Repeated TH experiments of ice crystals incubated in AFP solutions before and after the exchange of liquids in microfluidic devices gave the same TH activity. This finding clarifies our understanding of concentration dependence of TH. Furthermore, we found that hypAFPs protect ice against melting as well as freezing, resulting in superheated ice. Ice crystals were superheated up to 0.5�C above their equilibrium melting temperatures and remained stable in this superheated state for hours. Measurements of fast melting velocities added additional evidence to the observed superheating of ice in AFP solutions. The experimental results of the current study provide strong evidence that AFPs bind to ice surfaces via irreversible binding. We have demonstrated that the use of microfluidics in combination with fluorescence microscopy is a valuable technique to study the binding mechanisms of AFPs and the concentration dependence of AFP activity.
Celik, Yeliz
Non-one-dimensional and quasi-spherical loading of metal balls by shock-waves having up to 3 Mbar pressure, with the investigation of the preserved samples
NASA Astrophysics Data System (ADS)
Solid steel, brass and duralumin balls with 60 and 40 mm in diameter were exposed to explosion of spherical explosive charge 10 and 20 mm thick respectively. The explosion was initiated on the charge surface simultaneously in 2, 4 and 12 points, distributed uniformly over the sphere. To preserve the balls, massive case was used in test. In the diametral plane of section there were found either cracks, distributing mainly along the shock-waves collision lines, or the cavity. In most cases, the cavity was surrounded by the metal layer, having dendritic structure. In balls in case of explosion initiation in 12 points the metal motion was quasi-spherical (one-dimensional), in case of initiation in 2 points-two-dimensional and in 4 points-three-dimensional. The pressure evaluations, base on the convergent motion, as well as on the value of the residual temperature on the boundary of dendrits zone, showed, that inside crystallization zone the pressure exceede 2 Mbar.
Litvinov, B. V.; Zel'Dovich, V. I.; Purygin, N. P.; Khomskaya, I. V.; Buzanov, V. I.; Kheifetz, A. E.; Rinkevich, O. S.; Frolova, N. Yu.; Sobyanina, G. A.
Photonic crystal fiber monitors for intracellular ice formation
NASA Astrophysics Data System (ADS)
An all-silica steering wheel photonic crystal fiber (SW-PCF) device with real-time analysis for cellular temperature sensing is presented. Results are provided for water-filled SW-PCF fibers experiencing cooling down near -40�C. Cellular temperature sensors with fast response times are of interest particularly to the study of cryopreservation, which has been influential in applications such as tissue preservation, food quality control, genetic engineering, as well as drug discovery and in- vitro toxin testing. Results of this investigation are relevant to detection of intracellular ice formation (IIF) and better understanding cell freezing at very low temperatures. IIF detection is determined as a function of absorption occurring within the core of the SW-PCF. The SW-PCF has a 3.3?m core diameter, 125?m outer diameter and steering wheel-like air hole pattern with triangular symmetry, with a 20?m radius. One end of a 0.6m length of the SW-PCF is placed between two thermoelectric coolers, filled with ~0.1?L water. This end is butt coupled to a 0.5m length of single mode fiber (SMF), the distal end of the fiber is then inserted into an optical spectrum analyzer. A near-IR light source is guided through the fiber, such that the absorption of the material in the core can be measured. Spectral characteristics demonstrated by the optical absorption of the water sample were present near the 1300-1700nm window region with strongest peaks at 1350, 1410 and 1460nm, further shifting of the absorption peaks is possible at cryogenic temperatures making this device suitable for IIF monitoring applications.
Battinelli, Emily; Reimlinger, Mark; Wynne, Rosalind
Enhanced alignment of plate ice crystals in a non-uniform electric field
An atmospheric electric field exerts a torque on both column and plate ice crystals. Columns tend to align along the direction of the field. One diameter of plate crystals also aligns parallel to a field, while a non-uniform diverging field leads to further orientation and proscribes a secondary orientation along the direction of least divergence. A laboratory investigation treats the
T. C. Foster; J. Hallett
Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE
NASA Astrophysics Data System (ADS)
The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters, anvil cirrus formed about the Florida peninsula. A counter flow virtual impactor (CVI) was used to separate cirrus ice from the unactivated interstitial aerosol particles and evaporate condensed-phase water. Residual material, on a crystal-by-crystal basis, was subsequently analyzed using the NOAA Aeronomy Laboratory's Particle Analysis by Laser Mass Spectrometry (PALMS) instrument. Sampling was performed from 5 to 15 km altitude and from 12� to 28� north latitude within cirrus originating over land and ocean. Chemical composition measurements provided several important results. Sea salt was often incorporated into cirrus, consistent with homogeneous ice formation by aerosol particles from the marine boundary layer. Size measurements showed that large particles preferentially froze over smaller ones. Meteoritic material was found within ice crystals, indicative of a relation between stratospheric aerosol particles and tropospheric clouds. Mineral dust was the dominant residue observed in clouds formed during a dust transport event from the Sahara, consistent with a heterogeneous freezing mechanism. These results show that chemical composition and size are important determinants of which aerosol particles form cirrus ice crystals.
Cziczo, D. J.; Murphy, D. M.; Hudson, P. K.; Thomson, D. S.
The Growth of Atmospheric Ice Crystals: A Summary of Findings in Vertical Supercooled Cloud Tunnel Studies
Measurements of ice crystal growth under free fall in a generation of vertical supercooled cloud tunnels and some static cloud chambers as well as the related theoretical works are summarized.Growth parameters, that is, mass (m), dimensions, apparent density, and fall velocity (w), show extrema at about 5�, 10�, and 15�C where crystals are predominantly column-needle, isometric, and plate-stellar-dendrite, respectively. Crystal
Norihiko Fukuta; Tsuneya Takahashi
Investigation of nucleation, dynamic growth and surface properties of single ice crystals
NASA Astrophysics Data System (ADS)
Nucleation, dynamic growth and optical light scattering properties of a fixed single ice crystal have been experimentally characterized in dependence of both, the type of the ice nucleus (IN) and the prevailing thermodynamic conditions. The set up was developed based on the laminar flow tube LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratmann et al., 2004; Hartmann et al., 2011). The flow tube is equipped with a SID3-type (Small Ice Detector, Kaye et al., 2008) instrument called LISA (LACIS Ice Scattering Apparatus) and an additional optical microscope. For the investigations, a single (IN with a dry size of 2-10 micrometer is attached to a thin glass fiber and positioned within the optical measuring volume of LISA. The fixed particle is exposed to the thermodynamically controlled air flow, exiting the flow tube. Temperature and saturation ratio in the measuring volume can be varied on a time scale of 1-2 s by adjusting the humidified gas flow. Dependent on the thermodynamic conditions, ice nucleation and ice particle growth/shrinkage occur and can be studied. Thereby, the LISA instrument is applied to obtain 2-D light scattering patterns, and the additional optical microscope allows a time dependent visualization of the ice crystal. Both devices together allow to investigate the influence of the thermodynamic conditions on ice particle growth, the particle shape and its surface properties (i.e., its surface roughness, Ulanowski et al., 2011; Ulanowski et al., 2012; Ulanowski et al., 2013)). The thermodynamic conditions in the optical measuring volume have been extensively characterized using a) computational fluid dynamics (CFD) calculations, b) temperature and dew-point measurements, and c) evaluation of droplet and ice particle growth data. Furthermore, we successfully performed condensation freezing and deposition nucleation experiments with ATD (Arizona Test Dust), kaolinite, illite and SnomaxTM (Johnson Controls Snow, Colorado, USA) particles. In the experiments we could prove that different types of IN, as well as different temperatures and saturation ratios result in different growth rates and ice crystal shapes, but also in different surface properties. Regarding on single ice crystal, the surface roughness can also be modified by varying the prevailing thermodynamic conditions. Thereby, the surface roughness tends to increase for growing and to decrease for shrinking particles. Here, we will present current results of the thermodynamic characterization measurements and the ongoing ice crystal growth experiments.
Voigtlaender, Jens; Herenz, Paul; Chou, C�dric; Bieligk, Henner; Clauss, Tina; Niedermeier, Dennis; Ritter, Georg; Ulanowski, Joseph Z.; Stratmann, Frank
laboratory studies on the uptake of organic compounds by ice crystals
NASA Astrophysics Data System (ADS)
Anthropogenic aerosols produced from biomass burning are known to increase the number of cloud condensation nuclei in the atmosphere at most latitudes. This reduces cloud droplet size, which prevents raindrop formation at shallower levels in the atmosphere. Vertical convection processes force particles and water vapor to rise up to the upper troposphere. At lower temperatures, ice crystals are formed via heterogeneous freezing of supercooled droplets containing particles known as ice nuclei (IN) and/or via condensation of supercooled water onto IN directly from the vapor, followed by freezing. Ice crystals grow by vapor deposition, by collision of supercooled drops with ice particles and by collision of ice crystals. The grown ice crystals melt on their way down and turn into rain. Most of the precipitation falling to the surface at midlatitudes originates as ice. The adsorption of organic gases emitted from fossil fuel combustion like BTEX may alter particle growth and sublimation rates in the atmosphere. This may also change precipitation rates, which impact the climate world-wide. Considering importance of ice in atmospheric science, laboratory studies are carried out to quantify organic vapor adsorption onto ice. At temperatures between 0 and -40^oC, organic gases at ppb gas levels are allowed to adsorb to the surface of ice crystals with surface properties similar to atmospheric ice. For the experiments, a vertical ice chamber (stainless-steel) with 10 different screen inserts (stainless-steel) was constructed. The chamber is 39 cm in length and 10,5 cm in diameter. The size of the stainless-steel mesh of the screens was chosen by the size of the ice crystals and is 0.14 cm. The ice chamber is located inside a 2x2 m walk-in cold chamber. Prior to the addition of the organic gases, the precleaned carrier gas of synthetic air is humidified to ice saturation in the walk-in cold chamber by passing the carrier stream through a 10 m long and 5 cm in diameter aluminum pipe. Resulting super cooled droplets are removed by stainless-steel-wool. The carrier gas is mixed outside the ice chamber in various proportions with a defined gas mixture of 60 different organic compounds. This mixture is allowed to flow through the ice chamber at defined pressures and temperatures. The concentrations of the compounds in the gas phase are determined at the inlet and the outlet of the ice chamber by a mobile GC (AirmoVoc1020). Additionally, the amount of adsorbed compounds is determined by a very sensitive method based on solid-phase-micro-extraction (SPME) followed by GC/FID. The resulting sorption coefficients for different gas concentrations are plotted vs the reciprocal of the absolute temperature for all substances. First results dealing with the adsorption properties of the investigated organic compounds.
Fries, E.; Jaeschke, W.
Cirrus Clouds Millimeter-Wave Reflectivity Comparison with In-Situ Ice Crystal Airborne Data
In an effort to evaluate scattering models for particle size distributions of ice crystals within cirrus clouds, simultaneous data was collected during the Department of Energy (DoE) Atmospheric Radiation Measurement (ARM) Cloud Intensive operational period (Cloud IOP) at the Cloud and Radiation Testbed (CART) site in Lamont, Oklahoma, from the NCAR Video Ice Particle Sampler (VIPS) and UMass 33GHz\\/95GHz Cloud
Jos� Morales; Jorge Trabal; Sandra L. Cruz-Pol; Stephen M. Sekelsky
Snow crystal imaging using scanning electron microscopy: III. Glacier ice, snow and biota
Low-temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice obtained from South Cascade Glacier in Washington State, USA. Biotic samples consisting of algae (Chlamydomonas nivalis) and ice worms (a species of oligochaetes) were also collected and imaged. In the field, the snow and biological samples were mounted on copper plates, cooled in liquid nitrogen, and stored in dry shipping containers which maintain a temperature of -196??C. The firn and glacier ice samples were obtained by extracting horizontal ice cores, 8 mm in diameter, at different levels from larger standard glaciological (vertical) ice cores 7.5 cm in diameter. These samples were cooled in liquid nitrogen and placed in cryotubes, were stored in the same dry shipping container, and sent to the SEM facility. In the laboratory, the samples were sputter coated with platinum and imaged by a low-temperature SEM. To image the firn and glacier ice samples, the cores were fractured in liquid nitrogen, attached to a specimen holder, and then imaged. While light microscope images of snow and ice are difficult to interpret because of internal reflection and refraction, the SEM images provide a clear and unique view of the surface of the samples because they are generated from electrons emitted or reflected only from the surface of the sample. In addition, the SEM has a great depth of field with a wide range of magnifying capabilities. The resulting images clearly show the individual grains of the seasonal snowpack and the bonding between the snow grains. Images of firn show individual ice crystals, the bonding between the crystals, and connected air spaces. Images of glacier ice show a crystal structure on a scale of 1-2 mm which is considerably smaller than the expected crystal size. Microscopic air bubbles, less than 15 ??m in diameter, clearly marked the boundaries between these crystal-like features. The life forms associated with the glacier were easily imaged and studied. The low-temperature SEM sample collecting and handling methods proved to be operable in the field; the SEM analysis is applicable to glaciological studies and reveals details unattainable by conventional light microscopic methods.Low temperature scanning electron microscopy (SEM) was used to observe metamorphosed snow, glacial firn, and glacial ice obtained from South Cascade Glacier in Washington State, USA. Biotic samples consisting of algae and ice worms were also collected and imaged. The SEM images provide a clear and unique view of the surface of the samples because they are generated from electrons emitted or reflected only from the surface of the sample. The SEM has a great depth of field with a wide range of magnifying capabilities.
Rango, A.; Wergin, W. P.; Erbe, E. F.; Josberger, E. G.
Structural transformation in supercooled water controls the crystallization rate of ice.
One of water's unsolved puzzles is the question of what determines the lowest temperature to which it can be cooled before freezing to ice. The supercooled liquid has been probed experimentally to near the homogeneous nucleation temperature, T(H) ? 232 K, yet the mechanism of ice crystallization-including the size and structure of critical nuclei-has not yet been resolved. The heat capacity and compressibility of liquid water anomalously increase on moving into the supercooled region, according to power laws that would diverge (that is, approach infinity) at ~225 K (refs 1, 2), so there may be a link between water's thermodynamic anomalies and the crystallization rate of ice. But probing this link is challenging because fast crystallization prevents experimental studies of the liquid below T(H). And although atomistic studies have captured water crystallization, high computational costs have so far prevented an assessment of the rates and mechanism involved. Here we report coarse-grained molecular simulations with the mW water model in the supercooled regime around T(H) which reveal that a sharp increase in the fraction of four-coordinated molecules in supercooled liquid water explains its anomalous thermodynamics and also controls the rate and mechanisms of ice formation. The results of the simulations and classical nucleation theory using experimental data suggest that the crystallization rate of water reaches a maximum around 225 K, below which ice nuclei form faster than liquid water can equilibrate. This implies a lower limit of metastability of liquid water just below T(H) and well above its glass transition temperature, 136 K. By establishing a relationship between the structural transformation in liquid water and its anomalous thermodynamics and crystallization rate, our findings also provide mechanistic insight into the observed dependence of homogeneous ice nucleation rates on the thermodynamics of water. PMID:22113691
Moore, Emily B; Molinero, Valeria
Crystal alignments in the fast ice of Arctic Alaska
Field observations at 60 sites located in the fast or near-fast ice along a 1200-km stretch of the north coast of Alaska between the Bering Strait and Barter Island have shown that the great majority of the ice samples (95%) exhibit striking c axis alignments within the horizontal plane. In all cases the degree of preferred orientation increased with depth in the ice. Representative standard deviations around a mean direction in the horizontal plane are commonly less than +- 10/sup 0/ for samples collected near the bottom of the ice. At a given site the mean c axis direction X-bar/sub 0/ may vary as much as 20/sup 0/ with vertical location in the ice sheet. The c axis allignments in the nearshore region generally parallel the coast, with strong alignments occurring in the lagoon systems between the barrier islands and the coast and seaward of the barrier islands. In passes between islands and in entrances such as the opening to Kotzebue Sound the alignment is parallel to the channel. Only limited observations are available farther seaward over the inner (10- to 50-m isobaths) and outer (50-m isobath to shelf break) shelf regions. These indicate Ne-SW and E-W alignments, respectively, in the Beaufort Sea north of Prudhoe Bay.
Weeks, W.F.; Gow, A.J.
Dynamic pressure-induced dendritic and shock crystal growth of ice VI
Crystal growth mechanisms are crucial to understanding the complexity of crystal morphologies in nature and advanced technological materials, such as the faceting and dendrites found in snowflakes and the microstructure and associated strength properties of structural and icy planetary materials. In this article, we present observations of pressure-induced ice VI crystal growth, which have been predicted theoretically, but had never been observed experimentally to our knowledge. Under modulated pressure conditions in a dynamic-diamond anvil cell, rough single ice VI crystal initially grows into well defined octahedral crystal facets. However, as the compression rate increases, the crystal surface dramatically changes from rough to facet, and from convex to concave because of a surface instability, and thereby the growth rate suddenly increases by an order of magnitude. Depending on the compression rate, this discontinuous jump in crystal growth rate or �shock crystal growth� eventually produces 2D carpet-type fractal morphology, and moreover dendrites form under sinusoidal compression, whose crystal morphologies are remarkably similar to those predicted in theoretical simulations under a temperature gradient field. The observed strong dependence of the growth mechanism on compression rate, therefore, suggests a different approach to developing a comprehensive understanding of crystal growth dynamics.
Lee, Geun Woo; Evans, William J.; Yoo, Choong-Shik
From the single-scattering properties of ice crystals to climate prediction: A way forward
NASA Astrophysics Data System (ADS)
Cirrus is composed of non-spherical ice crystals, and against the blue background of the sky, they appear as tenuous wispy clouds, usually located at altitudes greater than about 6 km. Their spatial and temporal distribution about the Earth's atmosphere is significant. With such distributions, their contributions to the Earth's natural greenhouse effect and hydrological cycle are important. Therefore, it is important that climate models are able to predict the radiative effect of cirrus, as well as their contribution to the total amount of ice mass that occurs in the Earth's atmosphere. However, cirrus is composed of ice crystals that can take on a variety of geometrical shapes, from pristine habits such as hexagonal ice columns, hexagonal ice plates and bullet-rosettes, to highly randomized habits, which may have roughened surfaces and/or air cavities. These habits also aggregate together, to form chains of aggregates and compact aggregates. The sizes of these habits may also vary, from about less than 10 ?m, to several cm, with the smaller ice crystals usually existing toward cloud-top and the larger ice crystals existing toward the cloud-bottom. Due to this variability of geometrical complexity, size, and ice mass, predicting the magnitude of the cirrus greenhouse effect has proven problematic. To try to constrain these radiative and hydrological uncertainties, since about 2006 there is now available the A-train constellation of satellites, which attempt to quantify the radiative and hydrological contributions of cirrus to the Earth's atmosphere. The A-train obtains nearly simultaneous measurements of cirrus from across the electromagnetic spectrum. Such simultaneous measurements pose challenges for theoretical scattering models of cirrus, as these models must conserve ice mass and be physically consistent across the electromagnetic spectrum. In this review paper, the microphysical properties of cirrus are summarized. The current idealized habit mixture models that have been proposed to represent the observed variability in ice crystal shape, size and mass are discussed. The theoretical light scattering methods that are currently applied to the idealized habit mixture models to solve for their scattering and absorption properties are discussed. The physical inconsistency of the current approach to parameterize the bulk scattering and absorption properties of cirrus in climate models is highlighted. An alternative parameterization, which couples cloud physics more directly with radiation, is proposed. Such a coupling is required, if climate models are to be physically consistent and radiatively interactive.
Baran, Anthony J.
Crystal structure of an insect antifreeze protein and its implications for ice binding.
Antifreeze proteins (AFPs) help some organisms resist freezing by binding to ice crystals and inhibiting their growth. The molecular basis for how these proteins recognize and bind ice is not well understood. The longhorn beetle Rhagium inquisitor can supercool to below -25 �C, in part by synthesizing the most potent antifreeze protein studied thus far (RiAFP). We report the crystal structure of the 13-kDa RiAFP, determined at 1.21 ? resolution using direct methods. The structure, which contains 1,914 nonhydrogen protein atoms in the asymmetric unit, is the largest determined ab initio without heavy atoms. It reveals a compressed ?-solenoid fold in which the top and bottom sheets are held together by a silk-like interdigitation of short side chains. RiAFP is perhaps the most regular structure yet observed. It is a second independently evolved AFP type in beetles. The two beetle AFPs have in common an extremely flat ice-binding surface comprising regular outward-projecting parallel arrays of threonine residues. The more active, wider RiAFP has four (rather than two) of these arrays between which the crystal structure shows the presence of ice-like waters. Molecular dynamics simulations independently reproduce the locations of these ordered crystallographic waters and predict additional waters that together provide an extensive view of the AFP interaction with ice. By matching several planes of hexagonal ice, these waters may help freeze the AFP to the ice surface, thus providing the molecular basis of ice binding. PMID:23486477
Hakim, Aaron; Nguyen, Jennifer B; Basu, Koli; Zhu, Darren F; Thakral, Durga; Davies, Peter L; Isaacs, Farren J; Modis, Yorgo; Meng, Wuyi
A Model to Assess the Risk of Ice Accretion Due to Ice Crystal Ingestion in a Turbofan Engine and its Effects on Performance
NASA Technical Reports Server (NTRS)
The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was one or more of the following anomalies: degraded engine performance, engine roll back, compressor surge and stall, and flameout of the combustor. The main focus of this research is the development of a computational tool that can estimate whether there is a risk of ice accretion by tracking key parameters through the compression system blade rows at all engine operating points within the flight trajectory. The tool has an engine system thermodynamic cycle code, coupled with a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor blade rows. Assumptions are made to predict the complex physics involved in engine icing. Specifically, the code does not directly estimate ice accretion and does not have models for particle breakup or erosion. Two key parameters have been suggested as conditions that must be met at the same location for ice accretion to occur: the local wet-bulb temperature to be near freezing or below and the local melt ratio must be above 10%. These parameters were deduced from analyzing laboratory icing test data and are the criteria used to predict the possibility of ice accretion within an engine including the specific blade row where it could occur. Once the possibility of accretion is determined from these parameters, the degree of blockage due to ice accretion on the local stator vane can be estimated from an empirical model of ice growth rate and time spent at that operating point in the flight trajectory. The computational tool can be used to assess specific turbine engines to their susceptibility to ice accretion in an ice crystal environment.
Jorgenson, Philip C. E.; Veres, Joseph P.; Wright, William B.; Struk, Peter M.
On the Importance of Small Ice Crystals in Tropical Anvil Cirrus
NASA Technical Reports Server (NTRS)
In situ measurements of ice crystal concentrations and sizes made with aircraft instrumentation over the past two decades have often indicated the presence of numerous relatively small (< 50 m diameter) crystals in cirrus clouds. Further, these measurements frequently indicate that small crystals account for a large fraction of the extinction in cirrus clouds. The fact that the instruments used to make these measurements, such as the Forward Scattering Spectrometer Probe (FSSP) and the Cloud Aerosol Spectrometer (CAS), ingest ice crystals into the sample volume through inlets has led to suspicion that the indications of numerous small ]crystals could be artifacts of large ]crystal shattering on the instrument inlets. We present new aircraft measurements in anvil cirrus sampled during the Tropical Composition, Cloud, and Climate Coupling (TC4) campaign with the 2 ] Dimensional Stereo (2D ]S) probe, which detects particles as small as 10 m. The 2D ]S has detector "arms" instead of an inlet tube. Since the 2D ]S probe surfaces are much further from the sample volume than is the case for the instruments with inlets, it is expected that 2D ]S will be less susceptible to shattering artifacts. In addition, particle inter ]arrival times are used to identify and remove shattering artifacts that occur even with the 2D ]S probe. The number of shattering artifacts identified by the 2D ]S interarrival time analysis ranges from a negligible contribution to an order of magnitude or more enhancement in apparent ice concentration over the natural ice concentration, depending on the abundance of large crystals and the natural small ]crystal concentration. The 2D ]S measurements in tropical anvil cirrus suggest that natural small ]crystal concentrations are typically one to two orders of magnitude lower than those inferred from CAS. The strong correlation between the CAS/2D ]S ratio of small ]crystal concentrations and large ]crystal concentration suggests that the discrepancy is likely caused by shattering of large crystals on the CAS inlet. We argue that past measurements with CAS in cirrus with large crystals present may contain errors due to crystal shattering, and past conclusions derived from these measurements may need to be revisited. Further, we present correlations between CAS spurious concentration and 2D ]S large ]crystal mass from spatially uniform anvil cirrus sampling periods as an approximate guide for estimating quantitative impact of large ]crystal shattering on CAS concentrations in previous datasets. We use radiative transfer calculations to demonstrate that in the maritime anvil cirrus sampled during TC4, small crystals indicated by 2D ]S contribute relatively little cloud extinction, radiative forcing, or radiative heating in the anvils, regardless of anvil age or vertical location in the clouds. While 2D ]S ice concentrations in fresh anvil cirrus may often exceed 1 cm.3, and are observed to exceed 10 cm.3 in turrets, they are typically 0.1 cm.3 and rarely exceed 1 cm.3 (<1.4% of the time) in aged anvil cirrus. We hypothesize that isolated occurrences of higher ice concentrations in aged anvil cirrus may be caused by ice nucleation driven by either small ]scale convection or gravity waves. It appears that the numerous small crystals detrained from convective updrafts do not persist in the anvil cirrus sampled during TC ]4.
Jensen, E. J.; Lawson, P.; Baker, B.; Pilson, B.; Mo, Q.; Heymsfield, A. J.; Bansemer, A.; Bui, T. P.; McGill, M.; Hlavka, D.; Heymsfield, G.; Platnick, S.; Arnold, G. T.; Tanelli, S.
From parallel to single crystallization kinetics in high-density amorphous ice
NASA Astrophysics Data System (ADS)
The isobaric transformation behavior of unannealed (uHDA) and expanded (eHDA) high-density amorphous ice at pressures up to 0.20 GPa is compared using powder x-ray diffraction and dilatometry. eHDA shows high thermal stability and crystallizes to a single ice phase only, whereas uHDA shows much lower thermal stability and always crystallizes to a mixture of ice phases. Unexpectedly, at low temperatures hexagonal ice grows first from uHDA, whereas this phase never crystallizes from eHDA. This leads us to conclude that hidden structural order in the form of nanocrystalline domains is present in uHDA, which triggers growth of hexagonal ice. By contrast, these ordered domains are absent in eHDA, which appears to be a homogeneous material and, thus, could be considered as a candidate for the low-temperature proxy of the proposed high-density liquid phase of water. The present work provides the basis for further experimental studies aiming at investigating this possibility since it establishes that the well-studied uHDA is not the right material to be studied in this context, whereas the more recently discovered eHDA is.
Seidl, Markus; Amann-Winkel, Katrin; Handle, Philip H.; Zifferer, Gerhard; Loerting, Thomas
Elemental composition and morphology of ice-crystal residual particles in cirrus clouds and contrails
Aircraft sampling of residual particles from evaporated ice crystals was performed using a Counterflow Virtual Impactor. Samples of crystals taken in both contrails and cirrus clouds were compared with interstitial aerosols found in natural cirrus. The samples were analyzed with a scanning electron microscope which was equipped with a windowless energy-dispersive X-ray detector (SEM\\/EDX). In the contrail and cirrus cases
A Petzold; J Str�m; S Ohlsson; F. P Schr�der
Crystal growth of spin-ice pyrochlores by the floating-zone method
Single crystals of RE2Ti2O7 (RE=Y, Tb, Dy and Ho) have been grown by the floating-zone technique in an image furnace in a controlled atmosphere. The effect of annealing the crystals in different atmospheres was studied and found to be very important. Small amounts of Y were doped on the Dy site to study its effect on the spin-ice behaviour. Results
D. Prabhakaran; A. T. Boothroyd
Single particle measurements of the chemical composition of cirrus ice residue during CRYSTAL-FACE
The first real-time, in situ, investigation of the chemical composition of the residue of cirrus ice crystals was performed during July 2002. This study was undertaken on a NASA WB-57F high-altitude research aircraft as part of CRYSTAL-FACE, a field campaign which sought to further our understanding of the relation of clouds, water vapor, and climate by characterizing, among other parameters,
D. J. Cziczo; D. M. Murphy; P. K. Hudson; D. S. Thomson
Crystallization of amorphous ice as the cause of Comet P/Halley's outburst at 14 AU
NASA Technical Reports Server (NTRS)
An explanation is provided for the postperihelion eruption of Comet P/Halley, detected in February 1991 and believed to have started three months earlier, namely, the crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths of a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g/cu cm and a pore size of 1 micron crystallization occurs on the outbound leg of Comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond.
Prialnik, D.; Bar-Nun, A.
The effects of small ice crystals on cirrus infrared radiative properties
NASA Technical Reports Server (NTRS)
Using a model that combines single-scattering properties for spheroidal and hexagonal ice crystals, the thermal infrared radiative properties of cirrus clouds have been investigated. Infrared scattering and absorption properties for randomly oriented spheroids and hexagons are parameterized based on the anomalous diffraction theory and a geometric ray-tracing method, respectively. Using observed ice crystal size distributions, upwelling radiances at the top of cirrus cloudy atmospheres have been computed. Results show that the presence of small ice crystals can produce significant brightness temperature differences between two infrared wavelengths in the 10-micron window. Theoretical results have been compared with observed brightness temperature differences between 8.35 and 11.16 microns and between 11.16 and 12 microns. The observed values were obtained from the high-spectral resolution interferometer sounder. It is shown that the use of the present nonspherical model for ice crystals in radiative transfer calculations leads to a significantly better interpretation of the observed data than does the use of the spherical model.
Takano, Y.; Liou, K. N.; Minnis, P.
Initial stages in the morphological evolution of vapour-grown ice crystals: A laboratory investigation
SUMMARY We describe experiments to investigate the �rst stages in the evolution of small (100-200 ?m) ice crystals levitated in air at temperatures and humidities characteristic of fully glaciated stratiform clouds. We � nd that in these conditions particle morphology is not uniquely determined by environmental temperature and humidity as has commonly been assumed; other parameters, such as the mode
Neil J. Bacon; Marcia B. Baker; Brian D. Swanson
Depolarization of lidar returns by small ice crystals: An application to contrails
Measurements of the lidar linear depolarization ratio delta can be a powerful remote sensing technique for characterizing the microphysics of contrail particles. Since young contrails often consist of relatively small ice crystals, the quantitative interpretation of lidar measurements requires accurate theoretical computations of delta for polydisperse, randomly oriented nonspherical particles with size parameters ranging from zero to at least several
Michael I. Mishchenko; Kenneth Sassen
A global classification of snow crystals, ice crystals, and solid precipitation based on observations from middle latitudes to polar regions
NASA Astrophysics Data System (ADS)
This paper presents an extensive revision of Magono and Lee's (1966) classification of natural snow crystals, which has been widely used in snow and ice studies to describe snow crystal shapes. The new classification catalogs snow crystals and other solid precipitation particles into 121 categories, in contrast to Magono and Lee's 80 categories. Of these, 28 categories were created to classify new types of snow crystals that have been discovered in polar regions since 1968, seven were created after reconsidering the original categories, and six categories were created to classify solid precipitation particles such as frozen cloud particles and small raindrops. Because our observational area extended from middle latitudes (Japan) to polar regions, we refer to our new classification scheme as 'global-scale classification' or 'global classification'. The global classification consists of three levels - general, intermediate, and elementary - which are composed of 8, 39, and 121 categories, respectively. This paper describes the characteristics of each type of snow crystal, ice crystal, and solid precipitation particle.
Kikuchi, Katsuhiro; Kameda, Takao; Higuchi, Keiji; Yamashita, Akira
Lattice Boltzmann Simulation of Water Isotope Fractionation During Growth of Ice Crystals in Clouds
NASA Astrophysics Data System (ADS)
The isotopic composition of precipitation, especially that of snow, plays a special role in the global hydrological cycle and in reconstruction of past climates using polar ice cores. The fractionation of the major water isotope species (HHO, HDO, HHO-18) during ice crystal formation is critical to understanding the global distribution of isotopes in precipitation. Ice crystal growth in clouds is traditionally treated with a spherically- symmetric steady state diffusion model, with semi-empirical modifications added to account for ventilation and for complex crystal morphology. Although it is known that crystal growth rate, which depends largely on the degree of vapor over-saturation, determines crystal morphology, there are no existing quantitative models that directly relate morphology to the vapor saturation factor. Since kinetic (vapor phase diffusion-controlled) isotopic fractionation also depends on growth rate, there should be a direct relationship between vapor saturation, crystal morphology, and crystal isotopic composition. We use a 2D Lattice-Boltzmann model to simulate diffusion-controlled ice crystal growth from vapor- oversaturated air. In the model, crystals grow solely according to the diffusive fluxes just above the crystal surfaces, and hence crystal morphology arises from the initial and boundary conditions in the model and does not need to be specified a priori. The input parameters needed are the isotope-dependent vapor deposition rate constant (k) and the water vapor diffusivity in air (D). The values of both k and D can be computed from kinetic theory, and there are also experimentally determined values of D. The deduced values of k are uncertain to the extent that the sticking coefficient (or accommodation coefficient) for ice is uncertain. The ratio D/k is a length that determines the minimum scale of dendritic growth features and allows us to scale the numerical calculations to atmospheric conditions using a dimensionless Damkohler number: Da = kh/D, where h is the width of the 2D calculation domain. Varying the nondimensional Da in the model is equivalent to varying the scale (h) in the model. Our calculations confirm that the crystal/vapor isotopic fractionation approaches the equilibrium value, and the crystals are compact (circular in 2D) as the saturation factor approaches unity (S= 1.0). At higher oversaturation (e.g. S = 1.2), dendritic crystals of millimeter size develop on timescales appropriate to cloud processes, the isotopic fractionations are dominated by kinetic effects, and similar to those predicted by the spherical diffusion model. Dendritic crystals are constrained to be relatively large, with dimension much greater than D/k. The most difficult aspect of the modeling is to account for the large density difference between air and ice, which requires us to use a fictitious higher density for the vapor-oversaturated air and scale the crystal growth time accordingly. A different approach, using a larger scale simulation to derive boundary conditions for a nested smaller scale calculation is in progress. The results to date clarify the controls on dendritic crystal growth, the relationships between saturation state, growth rate, crystal morphology and isotopic fractionation, and provide limits on the value of the accommodation coefficient.
Lu, G.; Depaolo, D.; Kang, Q.; Zhang, D.
Characteristic of the ice crystal scattering database for GCOMC/SGLI satellite mission
NASA Astrophysics Data System (ADS)
In this study, we developed the ice crystal scattering database for ice cloud remote sensing and radiative transfer calculation of the Global Change Observation Mission (GCOMC)/Second Generation Global Imager (SGLI) satellite mission using light scattering methods of the LIght Scattering solver Applicable to particles of arbitrary Shape (LISAS)/ Geometrical-Optics Approximation (GOA), Surface Integral Equations Method of M�ller-type (SIEMM), Finite-Difference Time Domain (FDTD), and Improved Geometrical-Optics Method (IGOM). The GCOMC/SGLI mission measures essential geophysical parameters on the Earth's surface and in the atmosphere to facilitate understanding of the global radiation budget, which is scheduled to launch in around 2014 by the JAXA. Computing time and retrieval error of the effective particle radius is a main subject for developing the ice crystal scattering database for GCOMC satellite mission. For developing the suitable database, it is important to optimize the light scattering database based on the specification of the satellite sensor. There are two approaches to optimize a light scattering database: optimizing the complex refractive index grid system and optimizing the wavelength bin for a specific sensor channel. In the former method, a suitable grid system is determined by investigating the radiance error of radiative transfer calculations caused by differing fineness of step size of the complex refractive index. This study focuses on the former case. The grid system of the complex refractive index in the 1.6-?m (SW3) channel of the GCOMC/SGLI satellite sensor was investigated for optimizing the ice crystal scattering database. This grid system is separated into twelve patterns according to the step size of the real and imaginary parts of the refractive index. Specifically, the LISAS/ GOA technique is used to simulate the scattering of light by randomly oriented large hexagonal ice crystals. The difference of radiance with different ice cloud optical thickness and step size of the refractive index is calculated from developed light scattering database using the radiative transfer (R-STAR) solver. The results indicated that the step size of the real part is a significant factor in the difference of radiance. Furthermore, retrieval error of the effective particle radius caused by the sensor noise and error caused by refractive index grid system are investigated. Result indicated that, when step size of the real part is 0.04 with ice cloud optical thickness 8, total error of the effective particle radius is generally smaller than 2-?m. Hence, optimization of the refractive index in the SGLI channel is a significant step toward developing a suitable light scattering database for non-spherical ice crystals. Based on the above result, we developed the ice crystal scattering database for GCOMC satellite mission. Characteristic of the ice crystal scattering database for GCOMC/SGLI was investigated finally. Keywords: GCOMC/SGLI, ice crystal, light scattering method, effective particle radius
Letu, H.; Nakajima, T. Y.; Nagao, T. M.
Modeling variability in dendritic ice crystal backscattering cross sections at millimeter wavelengths using a modified Rayleigh-Gans theory
NASA Astrophysics Data System (ADS)
Using the Generalized Multi-particle Mie-method (GMM), Botta et al. (in this issue) [7] created a database of backscattering cross sections for 412 different ice crystal dendrites at X-, Ka- and W-band wavelengths for different incident angles. The Rayleigh-Gans theory, which accounts for interference effects but ignores interactions between different parts of an ice crystal, explains much, but not all, of the variability in the database of backscattering cross sections. Differences between it and the GMM range from -3.5 dB to +2.5 dB and are highly dependent on the incident angle. To explain the residual variability a physically intuitive iterative method was developed to estimate the internal electric field within an ice crystal that accounts for interactions between the neighboring regions within it. After modifying the Rayleigh-Gans theory using this estimated internal electric field, the difference between the estimated backscattering cross sections and those from the GMM method decreased to within 0.5 dB for most of the ice crystals. The largest percentage differences occur when the form factor from the Rayleigh-Gans theory is close to zero. Both interference effects and neighbor interactions are sensitive to the morphology of ice crystals. Improvements in ice-microphysical models are necessary to predict or diagnose internal structures within ice crystals to aid in more accurate interpretation of radar returns. Observations of the morphology of ice crystals are, in turn, necessary to guide the development of such ice-microphysical models and to better understand the statistical properties of ice crystal morphologies in different environmental conditions.
Lu, Yinghui; Clothiaux, Eugene E.; Aydin, K�ltegin; Botta, Giovanni; Verlinde, Johannes
Elementary steps at the surface of ice crystals visualized by advanced optical microscopy
Due to the abundance of ice on earth, the phase transition of ice plays crucially important roles in various phenomena in nature. Hence, the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. In this study we demonstrate, by laser confocal microscopy combined with differential interference contrast microscopy, that elementary steps (the growing ends of ubiquitous molecular layers with the minimum height) of ice crystals and their dynamic behavior can be visualized directly at air-ice interfaces. We observed the appearance and lateral growth of two-dimensional islands on ice crystal surfaces. When the steps of neighboring two-dimensional islands coalesced, the contrast of the steps always disappeared completely. We were able to discount the occurrence of steps too small to detect directly because we never observed the associated phenomena that would indicate their presence. In addition, classical two-dimensional nucleation theory does not support the appearance of multilayered two-dimensional islands. Hence, we concluded that two-dimensional islands with elementary height (0.37 and 0.39�nm on basal and prism faces, respectively) were visualized by our optical microscopy. On basal and prism faces, we also observed the spiral growth steps generated by screw dislocations. The distance between adjacent spiral steps on a prism face was about 1/20 of that on a basal face. Hence, the step ledge energy of a prism face was 1/20 of that on a basal face, in accord with the known lower-temperature roughening transition of the prism face.
Sazaki, Gen; Zepeda, Salvador; Nakatsubo, Shunichi; Yokoyama, Etsuro; Furukawa, Yoshinori
Antifreeze protein modulates cell survival during cryopreservation: mediation through influence on ice crystal growth.
Antifreeze proteins (AFPs) are extremely efficient at inhibiting ice recrystallization in frozen solutions. Knight and Duman [Knight, C. A. & Duman, J. G. (1986) Cryobiology 23, 256-263] have proposed that this may be an important function of the proteins in freeze-tolerant organisms. We have tested this proposal in vitro by characterizing the influence of AFP on the recovery of cryopreserved cells, which often can survive cooling and yet subsequently be damaged by ice crystal growth during warming. Relatively low concentrations (e.g., 5-150 micrograms/ml) of winter flounder (Pseudopleuronectes americanus) AFP enhance survival of red blood cells cryopreserved in hydroxyethyl starch solutions. This effect is most apparent in samples warmed at suboptimal rates, i.e., where ice recrystallization would be exaggerated. Cryomicroscopy demonstrates that AFP inhibits ice recrystallization in the extracellular regions during the latter stages of the warming cycle. AFP concentrations that enhance survival of red cells confer partial inhibition of recrystallization. Relatively high concentrations of AFP (e.g., 1.54 mg/ml) are much more effective at inhibiting extracellular recrystallization. However, extensive growth of ice around the cell, and concomitant cell damage, is noted. The mechanism for this AFP-induced ice growth is unknown. We propose that there is a delicate balance between AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell preservation and AFP-induced enhancement of cell damage and that this balance hinges on the degrees of inhibition of ice recrystallization and of preferential growth of ice around the cells. We conclude that, under appropriate conditions, one of the proposed functions of AFPs in nature can be emulated, and perhaps have application, in cryopreservation of materials of biomedical interest. PMID:1409591
Carpenter, J F; Hansen, T N
Single-scattering of preferentially oriented ice crystals at centimeter and millimeter wavelengths
NASA Astrophysics Data System (ADS)
The scattering properties of frozen cloud and precipitation particles at centimeter and millimeter wavelengths are fundamental for active and passive microwave remote sensing. So far the scattering parameters (scattering-, absorption-, and backscattering cross sections as well as asymmetry factor) have been calculated for randomly oriented particles only. However, some particle types, especially planar crystals, exhibit a preferred horizontal orientation. In this study the scattering and absorption parameters of four different planar ice crystal types have been modeled and exemplarily calculated from 1 GHz to 300 GHz with a freely available software code implementing the Discrete Dipole Approximation (DDA). It is presented how scattering and absorption of horizontally oriented ice crystals turn out for nadir-looking and inclined satellite sensors. The results show that small deviations around the horizontal orientation, as they are reported by relevant papers on cloud microphysics, have only marginal influence. Among all scattering parameters, the backscattering cross section of oriented crystals can differ most with respect to a random orientation. Especially if the incident wave direction is normal to the basal face, the parameter was found to be up to 20 times higher. Therefore the consideration of the orientation especially can be important for active microwave sensors. The more so if horizontally oriented particles and a nadir looking active sensor are involved. Furthermore the existing compilations for the index of refraction of ice at microwave frequencies have been reviewed.
Teschl, F.; Randeu, W. L.; Teschl, R.
Characterizing Single-Scattering Properties of Non-Spherical Ice-Crystal Ensembles
NASA Astrophysics Data System (ADS)
Retrievals of atmospheric particulate constituents using remote sensing means rely on the characterization of the single-scattering properties of these particulate matters. We are able to characterize with fairly high accuracies the single-scattering properties involving spherical particles, due to the symmetry of their shape. For example, it has been demonstrated that liquid water content, effective radius, and effective variance adequately characterize the single-scattering of an ensemble of spherical cloud water droplets in the visible and near-infrared wavelengths (Hansen and Travis 1974). Such is not the case, however, for non-spherical particles such as ice crystals. In order to characterize the scattering of these non-spherical particles we need to first find realistic representations of their shapes. The Snowfake (Gravner and Griffeath 2009) model is a numerical growth model for ice crystals based on diffusion and vapor deposition. It is capable of �growing� realistic ice crystals with the exquisite fine features observed in nature. Before the advent of Snowfake, single-scattering calculations are performed on shapes described by simplified mathematical formulae, which bear only a rough resemblance to the real ones. With crystals �grown� by the Snowfake model we can be more confident with the representativeness of the single-scattering properties obtained. Single-scattering properties of these particles are calculated using the open-source DDSCAT software developed by Draine and Flatau (2008), based on discrete dipole approximation (DDA). In this presentation we report early results obtained from the effort of characterizing the single-scattering of ensembles of pristine ice crystals using geometric parameters derived from the particle size distribution (PSD) of the ensembles at the wavelengths of current spaceborne radars.
Kuo, K.; Han, Q.; Smith, E. A.
NSDL National Science Digital Library
When a chunk of ice "twice the size of Manhattan" broke away from the northernmost part of the Antarctic Peninsula in February, ice was at the forefront of scientific news. Now, with the spectacular discovery of bacteria in Antarctic ice and with new evidence of slush beneath the frozen surface of Jupiter's moon Europa, water in its frozen form is once again in the news. The discovery of living organisms in the Antarctic ecosystem, described in the June 26, 1998 issue of Science, is significant because it presents a model for "how life may have arisen and persisted on other worlds." Scientists speculate that if organisms can thrive in the hard ice of Antarctica, they may possibly have done so on Europa and Mars. Galileo's closest approach to Europa occurred on July 21, 1998, offering new images of ice in space. The nine sites listed offer insights and details of the recent findings and discoveries related to ice.
Harris, Kathryn L.
General equations for the motions of ice crystals and water drops in gravitational and electric fields
NASA Technical Reports Server (NTRS)
General equations for the Reynolds number of a variety of types of ice crystals and water drops are given in terms of the Davies, Bond, and Knudsen numbers. The equations are in terms of the basic physical parameters of the system and are valid for calculating velocities in gravitational and electric fields over a very wide range of sizes and atmospheric conditions. The equations are asymptotically matched at the bottom and top of the size spectrum, useful when checking large computer codes. A numerical system for specifying the dimensional properties of ice crystals is introduced. Within the limits imposed by such variables as particle density, which have large deviations, the accuracy of velocities appears to be within 10 percent over the entire range of sizes of interest.
Nisbet, John S.
Charge Transfer Process During Collision of Riming Graupel Pellet with Small Ice Crystals within a Thundercloud
NASA Technical Reports Server (NTRS)
A charge transfer process during the collision of a riming graupel pellet and an ice-crystal at low temperature is proposed. During riming, the surface structure of graupel deviates from perfect crystalline structure. A concept of quasi-solid layer (QSL) formation on the surface is introduced. This QSL contains defects formed during riming. In absence of impurities, positively charged X-defect abundance is considered in the outer layer. These defects are assumed to be the charge carriers during the charge transfer process. Some part of the QSL is stripped off by the colliding ice crystals, which thereby gain some positive charge, leaving the graupel pellet negatively charged. With the proposed model, fC to pC of charge transfer is observed per collision. A transition temperature between -10 C to -15 C is also noted beyond which the QSL concept does not hold. This transition temperature is dependent on the bulk liquid water content of the cloud.
Datta, Saswati; De, Utpal K.; Goswami, K.; Jones, Linwood
Rheological Implications of the Internal Structure and Crystal Fabrics of the West Antarctic Ice Sheet as Revealed by Deep Core Drilling at Byrd Station.
National Technical Information Service (NTIS)
Crystalline textures and fabrics of ice cores from the 2164-m-thick ice sheet at Byrd Station, Antarctica, reveal the existence of an anisotropic ice sheet. A gradual but persistent increase in the c-axis preferred orientation of the ice crystals was obse...
A. J. Gow T. Williamson
The dependence of the single-scattering properties of small ice crystals on orientation average, particle shape, and wavelength
NASA Astrophysics Data System (ADS)
Current methods of representing the bulk scattering properties of cirrus for numerical models and satellite retrieval algorithms require weighting the single-scattering properties of specific shapes and sizes of ice crystals by their observed concentrations. Thus, to determine the influence of cirrus on solar and infrared radiation, as required for climate studies, knowledge of the single-scattering properties of ice crystals is required. Except for a few large ice crystals, most ice crystals do not have preferred orientations. Thus, the corresponding single-scattering properties of ice crystals used for numerical models and remote sensing retrievals are typically calculated assuming random orientations. The Euler's angle, selected using a random number generator, has been exclusively used to determine crystals' orientation for such calculations. When more orientations are used to determine the mean scattering properties, the scattering properties are determined with higher accuracy. However, computational resources limit the number of orientations that can be used in these calculations. Past studies used several efficient orientation-averaging schemes (e.g., quasi-Monte-Carlo and optimal cubature on the sphere) for calculating light scattering properties. These studies mainly focused on small sizes and considered relatively simple shapes, such as spheres and sphere aggregates. Atmospheric ice crystals are non-spherical and their sizes are much larger than those studied previously. In this study, the minimum numbers of orientations needed to determine the single-scattering properties of four different realistically shaped atmospheric ice crystals (i.e., column, droxtal, Gaussian random sphere, and budding Bucky ball) with predefined accuracy levels are determined using the Amsterdam discrete dipole approximation (ADDA) ver. 1.0. The results of the calculations are also used to quantify how the scattering and absorption efficiency, the single-scattering albedo, asymmetry parameter, and scattering phase function depend on sphericity, a parameter that is defined as the ratio of the surface area of a sphere with the same volume of given particle to the surface area of the particle. To generate the random orientations of ice crystals, the Euler's angles are selected using a quasi-Monte-Carlo method that uses a number sequence instead of a random number generator; its efficiency is compared with that of the internal orientation average method of ADDA. Further, simulations with varying sizes of ice crystals determine the influences of ice crystal size on the minimum number of orientations required to achieve the desired accuracy of the single-scattering properties. The results are reported for three different wavelengths of incident light, non-absorbing (0.55 ?m), moderate absorbing (3.78 ?m), and strongly absorbing (11 ?m).
Um, J.; McFarquhar, G. M.
Evaluation of Morphological Change and Aggregation Process of Ice Crystals in Frozen Food by Using Fractal Analysis
NASA Astrophysics Data System (ADS)
Size and shape of ice crystals in frozen food materials are very important because they affect not only quality of foods but also the viability of industrial processing such as freeze-drying of concentration. In this study, 30%wt sucrose solution is used as test samples. For examining the effect of stabilizerspectine and xantan gum is added to the sucrose solution. They are frozen on the cold stage of microscope to be observed their growing ice crystals under the circumstance of -10�C. Their size and shape are measured and quantitatively evaluated by applying fractal analysis. lce crystal of complicated shape has large fractal dimension, and vice versa. It successflly categorized the ice crystals into two groups; one is a group of large size and complicated shape, and the other is a group of small size and plain shape. The critical crystal size between the two groups is found to become larger with increasing holding time. It suggests a phenomenological model for metamorphoses process of ice crystals. Further, it is indicated that xantan gum is able to suppress the smoothing of ice crystals.
Koshiro, Yoko; Watanabe, Manabu; Takai, Rikuo; Hagiwara, Tomoaki; Suzuki, Toru
A new method for producing artificial snow crystals using a mixture of salt and ice
NASA Astrophysics Data System (ADS)
It has been found that artificial snow crystals can be produced by a simple method using a mixture of salt and ice crushed into sherbet as the cooling material. The freezing mixture of about 100 g was contained in a small styrene cup (85 mm varnothing, 50 mm height). A black acrylic plate (25 mm varnothing, 2 mm thickness) was placed on the freezing mixture in the cup. The cup was placed in a closed plastic box (130�130�65 mm). The water vapour in the air trapped in the plastic box crystallized onto the surface of the acrylic plate and made a crystal 1-2 mm in size in 20 minutes. The artificial crystal is quite similar to natural snow crystals with excellent hexagonal symmetry. A model to explain the process of producing the artificial snow crystal has been proposed, insisting that the electric field due to the static electricity from the acrylic plate plays an important role in making the seeds for the crystal growth.
Suwa, Y.; Myint, H. H.; Kurniawan, H.; Ito, F.; Kagawa, K.
Crystallization of amorphous ice as the cause of comet P/Halley's outburst at 14 AU.
The post-perihelion eruption of comet P/Halley, detected in Feb. 1991 and believed to have started 3 months earlier, can be explained by crystallization of amorphous ice taking place in the interior of the porous nucleus, at depths a few tens of meters, accompanied by the release of trapped gases. Numerical calculations show that for a bulk density of 0.5 g cm-3 and a pore size of 1 millimicron crystallization occurs on the outbound leg of comet P/Halley's orbit, at heliocentric distances between 5 AU and 17 AU. The trapped gas is released and flows to the surface through the porous medium. It may also open wider channels, as the internal pressures obtained surpass the tensile strength of cometary ice. The outflowing gas carries with it grains of ice and dust, and thus can explain the large amounts of dust observed in the coma at 14.3 AU and beyond. The typical decline time of the process is found to be on the order of months, in agreement with observations. The rate of outgassing is two or three orders of magnitude higher than in quiescence. In an asymmetric, non-uniform nucleus--in contrast to the one-dimensional spherical model--the process should occur intermittently, such as was observed for comet P/Halley beyond 5 AU. PMID:11538062
Prialnik, D; Bar-Nun, A
Calorimetric determination of inhibition of ice crystal growth by antifreeze protein in hydroxyethyl starch solutions.
Differential scanning calorimetry and cryomicroscopy were used to investigate the effects of type I antifreeze protein (AFP) from winter flounder on 58% solutions of hydroxyethyl starch. The glass, devitrification, and melt transitions noted during rewarming were unaffected by 100 micrograms/ml AFP. Isothermal annealing experiments were undertaken to detect the effects of AFP-induced inhibition of ice crystal growth using calorimetry. A premelt endothermic peak was detected during warming after the annealing procedure. Increasing the duration or the temperature of the annealing for the temperature range from -28 and -18 degrees C resulted in a gradual increase in the enthalpy of the premelt endotherm. This transition was unaffected by 100 micrograms/ml AFP. Annealing between -18 and -10 degrees C resulted in a gradual decrease in the premelt peak enthalpy. This process was inhibited by 100 micrograms/ml AFP. Cryomicroscopic examination of the samples revealed that AFP inhibited ice recrystallization during isothermal annealing at -10 degrees C. Annealing at lower temperatures resulted in minimal ice recrystallization and no visible effect of AFP. Thus, the 100 micrograms/ml AFP to have a detectable influence on thermal events in the calorimeter, conditions must be used that result in significant ice growth without AFP and visible inhibition of this process by AFP. Images FIGURE 8
Hansen, T N; Carpenter, J F
Quasi-Spherical Approach: A Fast Method for Modeling of Seismic Wave Propagation in a 2D Slice of a Global Earth Model With Lateral Heterogeneity
NASA Astrophysics Data System (ADS)
We propose a new method for calculation of seismic wavefield propagating in a global earth model includes lateral heterogeneity. In the field of global waveform modeling, 2D or axisymmetric modeling has been used because full 3D modeling is too intensive for real application. Considering 2D modeling cannot correctly model 3D geometrical spreading effects, axisymmetric modeling is the most appropriate method for global seismology. However, axisymmetric modeling couldn't treat unaxisymmetrical structure with respect to the source axis. Furthermore the scattered and reflected waves from the symmetric continuation of the structure can be returned to the target zone as artificial numerical noise. In order to overcome these problems, we here propose an ultra efficient approach for modeling 3D elastic wavefield. We solve the elastodynamic equation for spherical coordinates not in the conventional spherical domain: (0 Toyokuni, G.; Takenaka, H.; Wang, Y.; Kennett, B. L. 2004-12-01
Toyokuni, G.; Takenaka, H.; Wang, Y.; Kennett, B. L.
An experimental study of the exposure of a droplet and an ice crystal cloud medium to CO2 laser pulses
The relation of the size and concentration of water droplets and ice particles in clouds created by an exploding ice crystal and a water droplet following exposure to CO2 laser pulses has been investigated experimentally. The intensity of the laser pulses was in the range 0.1-10 MW\\/sq cm, and the duration was 5-6 microseconds. The relationship between the size and
V. A. Belts; O. A. Volkovitskii; A. F. Dobrovolskii; E. V. Ivanov; Iu. V. Nasedkin
Radiative properties of visible and subvisible Cirrus: Scattering on hexagonal ice crystals
NASA Technical Reports Server (NTRS)
One of the main objectives of the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE) is to provide a better understanding of the physics of upper level clouds. The focus is on just one specific aspect of cirrus physics, namely on characterizing the radiative properties of single, nonspherical ice particles. The basis for further more extensive studies of the radiative transfer through upper level clouds is provided. Radiation provides a potential mechanism for strong feedback between the divergence of in-cloud radiative flux and the cloud microphysics and ultimately on the dynamics of the cloud. Some aspects of ice cloud microphysics that are relevant to the radiation calculations are described. Next, the Discrete Dipole Approximation (DDA) is introduced and some new results of scattering by irregular crystals are presented. The Anomalous Diffraction Theory (ADT) was adopted to investigate the scattering properties of even larger crystals. In this way the scattering properties of nonspherical particles were determined over a range of particle sizes.
Flatau, Piotr J.; Stephens, Graeme L.; Draine, Bruce T.
Accurate simulation of the optical properties of atmospheric ice crystals with the invariant imbedding T-matrix method
NASA Astrophysics Data System (ADS)
The invariant imbedding T-matrix method (II-TM) is employed to compute the optical properties of randomly oriented ice crystals of various shapes including hexagonal columns, hollow columns, droxtals, bullet rosettes and aggregates. The II-TM is shown to be numerically stable and capable of obtaining the single-scattering properties of hexagonal ice crystals with size parameters up to 150. The 22� and 46� halo peaks in the phase function of compact hexagonal ice crystals begin to emerge at a size parameter of approximately 80 and tend to become insensitive to particle size as the corresponding size parameter approaches 150. Furthermore, the II-TM solutions are shown to be in agreement with their counterparts based on the discrete dipole approximation (DDA) method and the pseudo-spectral time-domain (PSTD) method. In addition, the accuracy of the improved geometric-optics method (IGOM) is examined for randomly oriented hexagonal ice crystal cases over a wide size-parameter range from the resonant to geometric-optics regimes. The II-TM is also used to study the effects of particle surface roughness and internal inclusions on the single-scattering properties of ice particles.
Bi, Lei; Yang, Ping
Advanced Optical Diagnostics for Ice Crystal Cloud Measurements in the NASA Glenn Propulsion Systems Laboratory
NASA Technical Reports Server (NTRS)
A light extinction tomography technique has been developed to monitor ice water clouds upstream of a direct connected engine in the Propulsion Systems Laboratory (PSL) at NASA Glenn Research Center (GRC). The system consists of 60 laser diodes with sheet generating optics and 120 detectors mounted around a 36-inch diameter ring. The sources are pulsed sequentially while the detectors acquire line-of-sight extinction data for each laser pulse. Using computed tomography algorithms, the extinction data are analyzed to produce a plot of the relative water content in the measurement plane. To target the low-spatial-frequency nature of ice water clouds, unique tomography algorithms were developed using filtered back-projection methods and direct inversion methods that use Gaussian basis functions. With the availability of a priori knowledge of the mean droplet size and the total water content at some point in the measurement plane, the tomography system can provide near real-time in-situ quantitative full-field total water content data at a measurement plane approximately 5 feet upstream of the engine inlet. Results from ice crystal clouds in the PSL are presented. In addition to the optical tomography technique, laser sheet imaging has also been applied in the PSL to provide planar ice cloud uniformity and relative water content data during facility calibration before the tomography system was available and also as validation data for the tomography system. A comparison between the laser sheet system and light extinction tomography resulting data are also presented. Very good agreement of imaged intensity and water content is demonstrated for both techniques. Also, comparative studies between the two techniques show excellent agreement in calculation of bulk total water content averaged over the center of the pipe.
Bencic, Timothy J.; Fagan, Amy; Van Zante, Judith F.; Kirkegaard, Jonathan P.; Rohler, David P.; Maniyedath, Arjun; Izen, Steven H.
Solar radiative transfer in cirrus clouds. I - Single-scattering and optical properties of hexagonal ice crystals. II - Theory and computations of multiple scattering in an anisotropic medium
NASA Technical Reports Server (NTRS)
The light scattering and absorption programs of Cai and Liou (1982) and Takano and Jaweera (1985) are extended to include hexagonal ice crystals randomly and horizontally oriented in space. The scattering and polarization results for the ice crystals are calculated. The results are compared with measurement data. The single-scattering properties for horizontally oriented columns and plates are presented and used to explain halos and arcs observed in the atmopshere. In the second section, the theory and computations for multiple scattering in cirrus clouds containing oriented ice crystals are presented. The radiative transfer in clouds composed of horizontally oriented ice crystals is formulated. Also, reflected and transmitted intensities, planetary albedo, and polarization in multiple scattering by ice crystals are discussed.
Takano, Yoshihide; Liou, Kuo-Nan
Importance of aggregation and small ice crystals in cirrus clouds, based on observations and an ice particle growth model
NASA Technical Reports Server (NTRS)
The 1 November 1986 FIRE I case study was used to test an ice particle growth model which predicts bimodal size spectra in cirrus clouds. The model was developed from an analytically based model which predicts the height evolution of monomodal ice particle size spectra from the measured ice water content (IWC). Size spectra from the monomodal model are represented by a gamma distribution, N(D) = N(sub o)D(exp nu)exp(-lambda D), where D = ice particle maximum dimension. The slope parameter, lambda, and the parameter N(sub o) are predicted from the IWC through the growth processes of vapor diffusion and aggregation. The model formulation is analytical, computationally efficient, and well suited for incorporation into larger models. The monomodal model has been validated against two other cirrus cloud case studies. From the monomodal size spectra, the size distributions which determine concentrations of ice particles less than about 150 mu m are predicted.
Mitchell, David L.; Chai, Steven K.; Dong, Yayi; Arnott, W. Patrick; Hallett, John
The Response of Optical Array Spectrometers to Ice and Snow: A Study of Probe Size to Crystal Mass Relationships.
National Technical Information Service (NTIS)
This report is a summary of work performed by Particle Measuring Systems, Inc., to study the response of Optical Array Spectrometers to ice and snow crystals. The principle objective of this study was to perform laboratory, field and theoretical studies t...
R. G. Knollenberg
Finite-difference time domain method for light scattering by small ice crystals in three-dimensional space
The finite-difference time domain (FDTD) method for the solution of light scattering by nonspherical particles has been developed for small ice crystals of hexagonal shapes including solid and hollow columns, plates, and bullet rosettes commonly occurring in cirrus clouds. To account for absorption, we have introduced the effec- tive permittivity and conductivity to circumvent the required complex calculations in the
Ping Yang; K. N. Liou
Estimation of Cirrus Cloud Effective Ice Crystal Shapes using Visible Reflectances from Dual-Satellite Measurements
NASA Technical Reports Server (NTRS)
This study develops and examines a multiangle, multisatellite method for determining effective cloud particle shapes from reflectances observed at visible wavelengths. The technique exploits the significant differences in the various cloud particle shape phase functions near the backscatter direction to infer particle shape from a combination of views from a near-backscatter angle and a side scattering angle. Adding-doubling calculations confirm that the optimal viewing combinations include one near-backscatter angle and another between 60" and 150". Sensitivity to shape increases with solar zenith angle. A total of 28 collocated, visible images from pairs of currently operating meteorological satellites with the desired viewing combinations were analyzed for particle shape. Matching reflectances from images with optimal viewing angles clearly separates water droplet from ice crystal clouds. Reflectance pairs from matched pixels containing ice crystals can be explained by the range of selected microphysical models. The most common retrieved shapes correspond to combinations of hexagonal compacts (aspect ratio of unity), hexagonal columns, and bullet rosettes. Although no single microphysical model can account for the observed variability, taken together, the models used for retrieving cloud particle size by the Clouds and the Earth's Radiant Energy System and the Moderate Resolution Imaging Spectroradiometer Projects can account for most of the reflectance variability observed in this limited data set. Additional studies are needed to assess the uncertainties in retrieved shapes due to temporal and spatial mismatches, anisotropic and bright background reflectances, and calibration errors and to validate the retrieved shapes. While applicable to a limited number of dual-satellite viewing combinations for current research and operational meteorological satellites, this approach could be used most extensively to derive effective particle size, shape, and optical depth from a combination of an imaging satellite in an L1 orbit, like Triana, and any other lower Earth orbiting Satellites.
Chepfer, Helene; Minnis, Patrick; Young, David; Nguyen, Louis; Arduini, Robert F.
Laboratory Investigation of Direct Measurement of Ice Water Content, Ice Surface Area, and Effective Radius of Ice Crystals Using a Laser-Diffraction Instrument.
National Technical Information Service (NTIS)
The aircraft microphysics probe, PVM-100A, was tested in the Colorado State University dynamic cloud chamber to establish its ability to measure ice water content (IWC), PSA, and Re in ice clouds. Its response was compared to other means of measuring thos...
H. Gerber P. J. DeMott D. C. Rogers
An Interpretation of the Mechanisms of Ice-Crystal Formation Operative in the Lake Almanor Cloud-Seeding Program.
NASA Astrophysics Data System (ADS)
In a 1984 85 winter cloud-seeding program at Lake Almanor, California, indium sesquioxide (In2O3) aerosol particle generators were collocated with silver iodide (AgI) aerosol particle generators as a source of inert tracer aerosol. The In2O3 aerosol served as an indicator of the amount of AgI aerosol scavenged. Based on the aerosol emission rates, if AgI aerosol was only captured by scavenging processes, and played no part in forming ice crystals and snowfall, the silver to indium ratio (Ag:In) in the analyzed snow would be 0.8.Analysis of snow samples from the target area produced frequent Ag[ratio]In ratio values in excess of 1.1. In the snowfall at the closest sampling sites to the aerosol generator the high ratios of Ag[ratio]In cannot be explained by the contact-freezing ice formation mechanism. A mechanism with a much faster rate than possible by contact freezing is necessary to produce the high Ag[ratio]In ratios that were observed. Part of the AgI seeding aerosol functioned rapidly to produce ice crystals by a forced condensation-freezing mechanism immediately after generation, and those ice crystals contributed to the snowfall at those sites closest to the generator.
Chai, Steven K.; Finnegan, William G.; Pitter, Richard L.
Synchrotron-Based Far-IRAS Investigations of Ice on a Single-Crystal Transition Metal Oxide
Synchrotron-based Far-IR Reflection Absorption Spectroscopy (Far-IRAS) has been used to measure the optical response of multi-layers of water adsorbed on a cleaned and annealed Fe3O4(100) single crystal thin film on MgO(100) substrate in the grazing incidence geometry. Several features of the composite system have been observed. In particular, two derivative-type bands at 700 and 800 cm-1 have been attributed to the librations of ice, and an anti-absorption band at 200 cm-1 has been assigned to the hindered translations of ice.
Hirschmugl, Carol J.; Peden, Charles HF.; Takasaki, M; Collins, M A.; Chambers, Scott A.; G Lawrence Carr and Paul Dumas
Formation of ridges on Europa above crystallizing water bodies inside the ice shell
NASA Astrophysics Data System (ADS)
Jupiter�s second Galilean satellite, Europa, is a Moon-sized body with an icy shell and global ocean approximately 100 km thick surrounding a rocky interior. Its surface displays extensive tectonic activity in a geologically recent past. Europa�s most ubiquitous surface features, double ridges, have a central trough flanked by two raised edifices. Double ridges can extend hundreds of kilometers and appear genetically related to cracks formed in the Europan ice shell. The origin of the raised flanks has been the center of much debate and many models have been proposed. There are also ridges without a central trough, single ridges. These ridges are far less common than their double ridge counterparts. However, there are locations where along-strike changes in ridge type appear to occur. We explore an elastic model in which the ridges form in response to crystallization of a liquid water intrusion. In our model, liquid water fills tension cracks that open in the Europan crust in response to tidal stress or perhaps overpressure of a subsurface ocean. The crack would be long and essentially continuous, similar to dikes on Earth, explaining the remarkable continuity and lack of segmentation of Europan ridges. The freezing of the water would cause a volume expansion, compressing and buckling the adjacent crust. We find that the geometry of the intruding water body controls the shape of the resulting ridges, with single ridges forming above sill-like intrusions and double ridges above dike-like intrusions. In order to match the ridge heights observed for double ridges we would need approximately 1.5 km2 of water intruded at a shallow depth in the ice shell, potentially over the course of multiple events. Deeper intrusions result in a broader, lower amplitude ridge than shallow intrusions.
Johnston, Stephanie A.; Mont�si, Laurent G. J.
Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters
NASA Astrophysics Data System (ADS)
A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (a polymorph of CaCO3�6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here, we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from a melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice floe thickness by 0.2 m per week and resulted in an estimated 3.8 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 10.6 mmol m-2 sea ice d-1 or to 3.3 ton km-2 ice floe week-1. This is markedly higher than the estimated primary production within the ice floe of 0.3-1.3 mmol m-2 sea ice d-1. Finally, the presence of ikaite in sea ice and the dissolution of the mineral during melting of the sea ice and mixing of the melt water into the surface oceanic mixed layer accounted for half of the estimated pCO2 uptake.
Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.
Ikaite crystals in melting sea ice - implications for pCO2 and pH levels in Arctic surface waters
NASA Astrophysics Data System (ADS)
A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO2 exchange. This has been complicated by the recent discoveries of ikaite (CaCO3�6H2O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO2 and pH conditions in surface waters. Here we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from an actively melting 1.7 km2 (0.5-1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures gradually disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice flow thickness by ca. 0.2 m per week and resulted in an estimated 1.6 ppm decrease of pCO2 in the ocean surface mixed layer. This corresponds to an air-sea CO2 uptake of 11 mmol m-2 sea ice d-1 or to 3.5 ton km-2 ice floe week-1.
Rysgaard, S.; Glud, R. N.; Lennert, K.; Cooper, M.; Halden, N.; Leakey, R. J. G.; Hawthorne, F. C.; Barber, D.
Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing
NASA Astrophysics Data System (ADS)
The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote-sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. Information on the spectral absorption of solar radiation by ice and liquid water cloud particles is derived from airborne measurements of solar spectral radiation reflected by these clouds. It is shown by calculation of the vertical weighting function of the measurements that the observed absorption of solar radiation is dominated by the upper cloud layers (50% within 200 m from cloud top). This vertical weighting function is shifted even closer to cloud top for wavelengths where absorption by ice dominates. On this basis an indicator of the vertical distribution of ice crystals in ABM clouds is designed. Applying in situ measured microphysical properties, the cloud-top reflectivity was calculated by radiative transfer simulations and compared to the measurements. It is found that ice crystals near cloud top (mixed-phase cloud top layer) are necessary to reproduce the measurements at wavelengths where absorption by ice dominates. The observation of backscatter glories on the cloud top generally indicating liquid water droplets does not contradict the postulated presence of ice crystals. Radiative transfer simulations reproduce the observed glories even if the cloud top layer is of mixed-phase character.
Ehrlich, A.; Wendisch, M.; Bierwirth, E.; Gayet, J.-F.; Mioche, G.; Lampert, A.; Mayer, B.
Evidence of ice crystals at cloud top of Arctic boundary-layer mixed-phase clouds derived from airborne remote sensing
NASA Astrophysics Data System (ADS)
The vertical distribution of ice crystals in Arctic boundary-layer mixed-phase (ABM) clouds was investigated by airborne remote sensing and in situ measurements during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. From airborne measurements of spectral solar radiation reflected by the ABM clouds information on the spectral absorption of solar radiation by ice and liquid water cloud particles is derived. It is shown by calculation of the vertical weighting function of the measurements that the observed absorption of solar radiation is dominated by the upper cloud layers (50% within 200 m from cloud top). This vertical weighting function is shifted even closer to cloud top for wavelengths where absorption by ice is dominating. On this basis an indicator of the vertical distribution of ice crystals in ABM clouds is designed. Applying the in situ measured microphysical properties, the cloud top reflectance was calculated by radiative transfer simulations and compared to measurements. It is found that ice crystals near cloud top (mixed-phase cloud top layer) are necessary to reproduce the measurements at wavelengths where absorption by ice is dominating. The observation of backscatter glories on top of the ABM clouds generally indicating liquid water droplets does not contradict the postulated presence of ice crystals. Radiative transfer simulations reproduce the observed glories even if the cloud top layer is of mixed-phase character.
Ehrlich, A.; Wendisch, M.; Bierwirth, E.; Gayet, J.-F.; Mioche, G.; Lampert, A.; Mayer, B.
Midlatitude Cirrus Clouds Derived from Hurricane Nora: A Case Study with Implications for Ice Crystal Nucleation and Shape
NASA Technical Reports Server (NTRS)
Hurricane Nora traveled up the Bala Peninsula coast in the unusually warm El Nino waters of September 1997, until rapidly decaying as it approached Southern California on 24 September. The anvil cirrus blowoff from the final surge of tropical convection became embedded in subtropical flow that advected the cirrus across the western US, where it was studied from the Facility for Atmospheric Remote Sensing (FARS) in Salt Lake City, Utah. A day later, the cirrus shield remnants were redirected southward by midlatitude circulations into the Southern Great Plains, providing a case study opportunity for the research aircraft and ground-based remote sensors assembled at the Clouds and Radiation Testbed (CART) site in northern Oklahoma. Using these comprehensive resources and new remote sensing cloud retrieval algorithms, the microphysical and radiative cloud properties of this unusual cirrus event are uniquely characterized. Importantly, at both the FARS and CART sites the cirrus generated spectacular optical displays, which acted as a tracer for the hurricane cirrus, despite the limited lifetimes of individual ice crystals. Lidar polarization data indicate widespread regions of uniform ice plate orientations, and in situ particle masticator data show a preponderance of pristine, solid hexagonal plates and columns. It is suggested that these unusual aspects are the result of the mode of cirrus particle nucleation, presumably involving the lofting of sea-salt nuclei in thunderstorm updrafts into the upper troposphere. This created a reservoir of haze particles that continued to produce halide-saltcontaminated ice crystals during the extended period of cirrus cloud maintenance. The reference that marine microliters are embedded in the replicas of ice crystals collected over the CART site points to the longevity of marine effects. Various nucleation scenarios proposed for cirrus clouds based on this and other studies, and the implications for understanding cirrus radiative properties or a global scale, are discussed.
Sassen, Kenneth; Arnott, W. Patrick; OCStarr, David; Mace, Gerald G.; Wang, Zhien; Poellot, Michael R.
Effects of Ice-Crystal Structure on Halo Formation: Cirrus Cloud Experimental and Ray-Tracing Modeling Studies
NASA Technical Reports Server (NTRS)
During the 1986 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) field campaign, four 22 deg halo-producing cirrus clouds were studied jointly from a ground-based polarization lidar and an instrumented aircraft. The lidar data show the vertical cloud structure and the relative position of the aircraft, which collected a total of 84 slides by impaction, preserving the ice crystals for later microscopic examination. Although many particles were too fragile to survive impaction intact, a large fraction of the identifiable crystals were columns and radial bullet rosettes, with both displaying internal cavitations and radial plate-column combinations. Particles that were solid or displayed only a slight amount of internal structure were relatively rare, which shows that the usual model postulated by halo theorists, i.e., the randomly oriented, solid hexagonal crystal, is inappropriate for typical cirrus clouds. With the aid of new ray-tracing simulations for hexagonal hollow-ended column and bullet-rosette models, we evaluate the effects of more realistic ice-crystal structures on halo formation and lidar depolarization and consider why the common halo is not more common in cirrus clouds.
Sassen, Kenneth; Knight, Nancy C.; Takano, Yoshihide; Heymsfield, Andrew J.
The effect of dynamic compression on phase transformation: Solidification of water and crystal growth of ice VI using dynamic diamond anvil cell
NASA Astrophysics Data System (ADS)
The kinetics of phase transformation depends on how driving parameters are applied. Under high pressure, compression rate can give different paths of phase transformation. For this purpose, we have developed a new device, called dynamic diamond anvil cell (d-DAC), which can modulate a given static pressure with various compression rate and type. Using d-DAC, liquid water can be overpressurized up to 75 % in ice VI phase field without crystallization, and after transforms to metastable iceVII phase in the stable ice VI pressure field. Interestingly, when fast sinusoidal compression is applied, the crystal morphology of ice VI surrounded by liquid water dramatically changes to fractal and dendritic shape. In this talk, we will describe the details of crystallization, following a brief description of the technical development of d-DAC.
Lee, Geun Woo; Evans, William; Yoo, Choong-Shik
NSDL National Science Digital Library
In this chemistry activity, learners use the lowered freezing point of water to chill another mixture (ice cream) to the solid state. Learners will record the temperature of the ice before and after mixing it with the ice cream ingredients and discover that adding a solute to a solvent lowers the freezing point of that solvent (also known as a colligative property). This activity can also be used to introduce learners to crystallization.
House, The S.
Stability relationship for water droplet crystallization with the NASA Lewis icing spray nozzle
In order to produce small droplets for icing cloud simulation, high pressure air atomizing nozzles are used. For certain icing testing applications, median drop sizes as small as 5 mm are needed, which require air atomizing pressures greater than 3000 kPa. Isentropic expansion of the ambient temperature atomizing air to atmospheric pressure can result in air stream temperatures of -160
C. John Marek; C. Scott Bartlett
Scattering of Polarized Light by Ice Crystals and Monodispersed Ellipsoidal Latex Particles
The large coolable and evacuable aerosol chamber AIDA is used as a cloud chamber to study processes of ice formation in atmospheric clouds and in the upper troposphere. In- tensity and depolarization of forward- and back-scattered laser radiation is measured, caused by particles in a small scattering volume far from the walls. Droplet freezing and growth of the ice particles
A. Nink; H. Bunz; O. M�hler; M. Schnaiter; R. Tiede; U. Schurath
Polarimetric radar observation of ice crystals and aggregates: Backscattering modeling of signatures from C to Ka band
NASA Astrophysics Data System (ADS)
Hydrometeor classification using polarimetric Doppler weather radar is based on the characteristic polarimetric signature for each hydrometeor class. This signature can be obtained by either experimental campaigns or by proper electromagnetic modelling. Both approaches have advantages and drawbacks: the experimental approach is not easy to conduct as it requires co-located measurements of a weather radar with in-situ sampler (usually installed aboard an aircraft); moreover, it is generally strictly related to the measurement configuration (e.g., frequency, range) it is performed. Of course, experimental campaigns are needed for definitive validation, but the modelling approach exhibits a high flexibility in terms of system and meteorological parameters very well suited for retrieval algorithm design. On the other hand, a model approach is heavily dependent on the model capability to represent hydrometeor volumes in a realistic way. Within the electromagnetic scattering modelling of hydrometeor radar response, a well known technique to simulate the radar backscattering from an ensemble of particle is based on the T-matrix algorithm (Kim, 2006). The T-matrix model is based on the equivalence principle and can ensure numerical convergence for a small set of canonical shapes such as ellipsoids. These shapes are useful to represent raindrops and vertically-oriented small crystals, but are largely unrealistic when dealing with ice aggregates and crystals. In this work we use a different approach to the scattering modelling that fits well for classes like ice crystals and aggregates of different shapes and sizes: the discrete dipole approximation (DDA). The DDA model lets us simulate almost any kind of particle under the hypothesis it can be approximated as a three dimensional array of dipoles that generate the scattering field (the wavelength should be large compared to the distance between dipoles). The DDA code used is DDSCAT, developed by Draine and Flatau (2004), which computes the scattering by a single randomly oriented particle. With this approach a variety of hydrometeor shapes have been simulated: cylindrical ice crystals, aggregates of ice cylinders, snow crystals, mixed-phase particles, etc. From DDA it has been possible to obtain the polarimetric signature for ground-based radars at C and X band for these hydrometeor classes after solving some heavy computational issues. An equivalent spheroid model has been also developed for the ice hydrometeor classes in order to use a T-matrix code, faster than DDA, to simulate ice crystals-equivalent spheroids (Weinman and Kim, 2007). Numerical results will be discussed analyzing the sensitivity of the DDA model to the particle shape, wavelength, size distribution and orientation. The accuracy of T-matrix approximation of the ensemble particle polarimetric signature will be also evaluated within the context of hydrometeor classification schemes based on either fuzzy-logic or Bayesian techniques.
Botta, G.; Montopoli, M.; Marzano, F. S.
Validation and Determination of Ice Water Content - Radar Reflectivity Relationships during CRYSTAL-FACE: Flight Requirements for Future Comparisons
NASA Technical Reports Server (NTRS)
In order for clouds to be more accurately represented in global circulation models (GCM), there is need for improved understanding of the properties of ice such as the total water in ice clouds, called ice water content (IWC), ice particle sizes and their shapes. Improved representation of clouds in models will enable GCMs to better predict for example, how changes in emissions of pollutants affect cloud formation and evolution, upper tropospheric water vapor, and the radiative budget of the atmosphere that is crucial for climate change studies. An extensive cloud measurement campaign called CRYSTAL-FACE was conducted during Summer 2002 using instrumented aircraft and a variety of instruments to measure properties of ice clouds. This paper deals with the measurement of IWC using the Harvard water vapor and total water instruments on the NASA WB-57 high-altitude aircraft. The IWC is measured directly by these instruments at the altitude of the WB-57, and it is compared with remote measurements from the Goddard Cloud Radar System (CRS) on the NASA ER-2. CRS measures vertical profiles of radar reflectivity from which IWC can be estimated at the WB-57 altitude. The IWC measurements obtained from the Harvard instruments and CRS were found to be within 20-30% of each other. Part of this difference was attributed to errors associated with comparing two measurements that are not collocated in time an space since both aircraft were not in identical locations. This study provides some credibility to the Harvard and CRS-derived IWC measurements that are in general difficult to validate except through consistency checks using different measurement approaches.
Sayres, D. S.; Smith, J. B.; Pittman, J. V.; Weinstock, E. M.; Anderson, J. G.; Heymsfield, G.; Fridland, A. M.; Ackerman, A. S.
Effect of the grain boundary of ice crystals in a frozen gelatin solution on the dielectric properties at a subzero temperature.
The effect of the grain boundary of ice crystals in a frozen gelatin solution on the dielectric properties was investigated by the combination of a dielectric spectrometer and image analysis. A micro-slicer image processing system (MSIPS) was applied to measure the grain boundary properties as the perimeter density and number density of ice crystals. The perimeter density and number density of the ice crystals increased with increasing freezing rate. The dielectric properties of the frozen gelatin solution at various freezing rates were measured in the frequency range of 100 Hz to 100 kHz at -40 degrees C. The relaxation time did not affect the grain boundary properties. The perimeter density and number density significantly affected dielectric parameter epsilon(0)-epsilon(infinity) and electrical conductivity sigma(0). These results indicate that the dielectric spectrometer could be used to estimate the grain boundary properties in a frozen gelatin solution. PMID:19897916
Ueno, Shigeaki; Shirakashi, Ryo; Kudoh, Ken-ichi; Higuchi, Toshiro; Do, Gab-Soo; Araki, Tetsuya; Sagara, Yasuyuki
Freezing and melting behavior of an octyl ?-D-glucoside-water binary system--inhibitory effect of octyl ?-D-glucoside on ice crystal formation.
Phase transition behavior of lyotropic liquid crystals of an octyl ?-D-glucoside (OG)-water binary system during ice freezing and melting was studied by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Not the thermotropic, but the lyotropic phase transition due to the change of OG concentration during ice freezing and melting was observed. The concentration-temperature phase diagram of the binary system was constructed. Melting temperature of ice, T(m), lyotropic phase transition temperature, T(tr), and glass transition temperatures of unfrozen phases in the absence and presence of ice, T(g) and T(g)', were shown in the phase diagram. The phase diagram indicated that the OG aqueous system was concentrated to ca. 90-92 wt% by ice freezing and exhibited glass transition at T(g)'. An observation of the concentration-gradient specimen by the cryo-POM showed the evidence of the inhibitory effects of OG on nucleation and growth of ice crystals in the extremely high OG concentration system in which the lamellar liquid crystalline phase was formed. This study provided the importance of the influence of concentration change by ice freezing on the behaviour of the sugar-based surfactant-water system under low temperature conditions. PMID:23133837
Ogawa, Shigesaburo; Asakura, Kouichi; Osanai, Shuichi
Supercooled Droplets and Ice Crystals in Mixed-Phase Clouds: Numerical Simulations Considering Isotropic Turbulence of the Ambient Flow Field
NASA Astrophysics Data System (ADS)
In midlatitudes the formation and evolution of precipitation is the result of a chain of processes taking place in mixed-phase clouds. Due to the coexistence of supercooled water drops and ice particles in such clouds mutual interactions by collisions, i.e. riming and aggregation, take place leading to ice hydrometeors of a large precipitation size. In the past these collision mechanisms have been investigated - besides laboratory measurements - by numerical simulations of the collision process where trajectories of the participating hydrometeors have been calculated as occurring in an environment at rest (Pruppacher and Klett, Kluwer Academic Publishers, Dordrecht, 1997). However, as it is well-known the flow field in clouds is almost always turbulent (Siebert et al., Atmos. Res. 97 (2010) 426-437) except in undiluted updrafts of single strong convective clouds. And it has been argued that turbulence may enhance precipitation formation. As a consequence turbulence effects on the collisional interaction of cloud and other heavy particles came into focus during the last decade and gave rise to the description in terms of radial distribution function, mean radial relative velocity and the collection efficiency all derived from numerical simulations. Up to now mostly the turbulence influence on cloud droplet/cloud droplet collisions has been investigated (Ayala et al., New J. Phys. 10 (2008) 075015), (Bec et al., J. Fluid Mech. 646 (2010) 527-536). Much less is known about the influence of turbulence on particles in mixed phase clouds. This is mainly due to the various and complex shapes of the ice particles depending on the temperature, the supersaturation, and their life time. Hence, our knowledge about the behavior of ice crystals in turbulence is based on wind tunnel experiments. In the early stage ice crystals often have the shape of hexagonal plates or needles. In theoretical and numerical studies these are commonly approximated by ellipsoids. However, except in (Pinsky and Khain, Atmos. Res. 47-48 (1998) 69-86) only laminar flows have been considered so far. Therefore we have developed a numerical experiment with a novel setup (Kunnen et al., under review in Atmos. Res. (2013)). Therein synthetic turbulence is generated at the inflow and is then advected by a mean flow through the domain. The full Navier-Stokes equations are solved using a DNS method on an Eulerian Cartesian grid. The evolving decaying turbulence shares similarities with the grid-generated turbulence of wind tunnels. In this flow several million particle spheres as well as ellipsoids are advanced in a Lagrangian manner in order to represent the supercooled droplets and ice crystals out of a small region of a mixed-phase cloud. Statistics will be gathered about the orientation, the sedimentation velocities, the clustering, and the relative velocities of these particles. From this basis collision kernels can be calculated. These are input parameters for cloud models estimating the evolution of precipitation.
Siewert, Christoph; Kunnen, Rudie; Meinke, Matthias; Schr�der, Wolfgang; Beheng, Klaus
More accurate determination of the quantity of ice crystallized at low cooling rates in the glycerol and 1,2-propanediol aqueous solutions: comparison with equilibrium.
It is generally assumed that when cells are cooled at rates close to those corresponding to the maximum of survival, once supercooling has ceased, above the eutectic melting temperature the extracellular ice is in equilibrium with the residual solution. This did not seem evident to us due to the difficulty of ice crystallization in cryoprotective solutions. The maximum quantities of ice crystallized in glycerol and 1,2-propanediol solutions have been calculated from the area of the solidification and fusion peaks obtained with a Perkin-Elmer DSC-2 differential scanning calorimeter. The accuracy has been improved by several corrections: better defined baseline, thermal variation of the heat of fusion of the ice, heat of solution of the water from its melting with the residual solution. More ice crystallizes in the glycerol than in the 1,2-propanediol solutions, of which the amorphous residue contains about 40 to 55% 1,2-propanediol. The equilibrium values are unknown in the presence of 1,2-propanediol. With glycerol, in our experiments, the maximum is first lower than the equilibrium but approaches it as the concentration increases. It is not completely determined by the colligative properties of the solutes. PMID:6713947
Boutron, P
Ice rule correlations in stuffed spin ice
NASA Astrophysics Data System (ADS)
Stuffed spin ice is a chemical variation of a spin ice material like Ho2Ti2O7 in which extra magnetic ions are inserted into the crystal structure. Previous studies have shown that the degree of stuffing has very little effect on the residual entropy in the system, which takes a value very close to the spin ice entropy. We argue, however, that the observation of this entropy does not imply long range coherence of the ice rules, that determine the local spin configurations. We have characterized deviations from the ice rules by means of a polarized neutron diffraction study of a single crystal of Ho2+?Ti2-?O7-?/2 with ? = 0.3. Our results demonstrate that the ice rules in stuffed spin ice are strictly valid only over a relatively short range, and that at longer range stuffed spin ice exhibits some characteristics of a �cluster glass�, with a tendency to more conventional ferromagnetic correlations.
Aldus, R. J.; Fennell, T.; Deen, P. P.; Ressouche, E.; Lau, G. C.; Cava, R. J.; Bramwell, S. T.
Crystal structure and encapsulation dynamics of ice II-structured neon hydrate.
Neon hydrate was synthesized and studied by in situ neutron diffraction at 480 MPa and temperatures ranging from 260 to 70 K. For the first time to our knowledge, we demonstrate that neon atoms can be enclathrated in water molecules to form ice II-structured hydrates. The guest Ne atoms occupy the centers of D2O channels and have substantial freedom of movement owing to the lack of direct bonding between guest molecules and host lattices. Molecular dynamics simulation confirms that the resolved structure where Ne dissolved in ice II is thermodynamically stable at 480 MPa and 260 K. The density distributions indicate that the vibration of Ne atoms is mainly in planes perpendicular to D2O channels, whereas their distributions along the channels are further constrained by interactions between adjacent Ne atoms. PMID:25002464
Yu, Xiaohui; Zhu, Jinlong; Du, Shiyu; Xu, Hongwu; Vogel, Sven C; Han, Jiantao; Germann, Timothy C; Zhang, Jianzhong; Jin, Changqing; Francisco, Joseph S; Zhao, Yusheng
Crystal Distortion of Dy2Ti2O7 at the Spin Ice Transition Temperature
Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1\\/2. The Dy ions reside on the vertices of corner-linked tetrahedra. Due to a strong single-ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local quantization axes. We measured the
H. Suzuki; F. Hata; Y. Xue; H. Kaneko; A. Hosomichi; S. Abe; R. Higashinaka; S. Nakatsuji; Y. Maeno
Cloud Resolving Simulations of Mixed-Phase Arctic Stratus Observed during BASE: Sensitivity to Concentration of Ice Crystals and Large-Scale Heat and Moisture Advection.
NASA Astrophysics Data System (ADS)
The authors' previous idealized, two-dimensional cloud resolving model (CRM) simulations of Arctic stratus revealed a surprising sensitivity to the concentrations of ice crystals. In this paper, simulations of an actual case study observed during the Beaufort and Arctic Seas Experiment are performed and the results are compared to the observed data.It is again found in the CRM simulations that the simulated stratus cloud is very sensitive to the concentration of ice crystals. Using midlatitude estimates of the availability of ice forming nuclei (IFN) in the model, the authors find that the concentrations of ice crystals are large enough to result in the almost complete dissipation of otherwise solid, optically thick stratus layers. A tenuous stratus can be maintained in the simulation when the continuous input of moisture through the imposed large-scale advection is strong enough to balance the ice production. However, in association with the large-scale moisture and warm advection, only by reducing the concentration of IFN to 0.3 of the midlatitude estimate values can a persistent, optically thick stratus layer be maintained. The results obtained from the reduced IFN simulation compare reasonably well with observations.The longwave radiative fluxes at the surface are significantly different between the solid stratus and liquid-water-depleted higher ice crystal concentration experiments.This work suggests that transition-season Arctic stratus can be very vulnerable to anthropogenic sources of IFN, which can alter cloud structure sufficiently to affect the rates of melting and freezing of the Arctic Ocean.The authors find that the Hallett-Mossop riming splintering mechanism is not activated in the simulations because the cloud droplets are very small and cloud temperatures are outside the range supporting efficient rime splintering. Thus, the conclusions drawn from the results presented in this paper may be applicable to only a limited class of Arctic stratus.
Jiang, Hongli; Cotton, William R.; Pinto, James O.; Curry, Judy A.; Weissbluth, Michael J.
Isothermal Ice-Crystallization Kinetics in the Gas-Diffusion Layer of a Proton-Exchange-Membrane Fuel Cell
Nucleation and growth of ice in the fibrous gas-diffusion layer (GDL) of a proton-exchange membrane fuel cell (PEMFC) are investigated using isothermal differential scanning calorimetry (DSC). Isothermal crystallization rates and pseudo-steady-state nucleation rates are obtained as a function of subcooling from heat-flow and induction-time measurements. Kinetics of ice nucleation and growth are studied at two polytetrafluoroethylene (PTFE) loadings (0 and 10 wt %) in a commercial GDL for temperatures between 240 and 273 K. A nonlinear icecrystallization rate expression is developed using Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory, in which the heat-transfer-limited growth rate is determined from the moving-boundary Stefan problem. Induction times follow a Poisson distribution and increase upon addition of PTFE, indicating that nucleation occurs more slowly on a hydrophobic fiber than on a hydrophilic fiber. The determined nucleation rates and induction times follow expected trends from classical nucleation theory. A validated rate expression is now available for predicting icecrystallization kinetics in GDLs.
Dursch, Thomas J.; Ciontea, Monica A.; Radke, Clayton J.; Weber, Adam Z.
Optical Spectra of Orientationally Disordered Crystals. II. Infrared Spectrum of Ice Ih and Ice Ic from 360 to 50 cm-1
The far-infrared spectra in the range 360�50 cm?1 of ice Ih and ice Ic made from H2O and from D2O, and of vitreous ice made made from H2O have been investigated. The spectra are due to essentially purely translational vibrations, and have been interpreted using the theory of the spectra of orientationally disordered phases developed in the preceding paper. There
J. E. Bertie; E. Whalley
Chemical Characterization of Individual Particles and Residuals of Cloud Droplets and Ice Crystals Collected On Board Research Aircraft in the ISDAC 2008 Study
Although it has been shown that size of atmospheric particles has a direct correlation with their ability to act as cloud droplet and ice nuclei, the influence of composition of freshly emitted and aged particles in nucleation processes is poorly understood. In this work we combine data from field measurements of ice nucleation with chemical imaging of the sampled particles to link aerosol composition with ice nucleation ability. Field measurements and sampling were conducted during the Indirect and Semidirect Aerosols Campaign (ISDAC) over Barrow, Alaska, in the springtime of 2008. In-situ ice nucleation measurements were conducted using a Continuous Flow Diffusion Chamber (CFDC). Measured number concentrations of ice nuclei (IN) varied from frequent values of 0.01 per liter to more than 10 per liter. Residuals of airborne droplets and ice crystals were collected through a counterflow virtual impactor (CVI). The compositions of individual atmospheric particles and the residuals were studied using Computer Controlled Scanning Electron Microscopy with Energy Dispersive X-ray analysis (CCSEM/EDX) and Scanning Transmission X-ray Microscopy coupled with Near Edge X-ray Absorption Fine Structure spectroscopy (STXM/NEXAFS). Chemical analysis of cloud particle residuals collected during an episode of high ice nucleation suggests that both size and composition may influence aerosol's ability to act as IN. The STXM/NEXAFS chemical composition maps of individual residuals have characteristic structures of either inorganic or black carbon cores coated by organic materials. In a separate flight, particle samples from a biomass burning plume were collected. Although it has previously been suggested that episodes of biomass burning contribute to increased numbers of highly effective ice nuclei, in this episode we observed that only a small fraction were effective ice nuclei. Most of the particles from the biomass plume episode were smaller in size and were composed of homogeneous organic material without identifiable cores.
Hiranuma, Naruki; Brooks, Sarah D.; Moffet, Ryan C.; Glen, Andrew; Laskin, Alexander; Gilles, Marry K.; Liu, Peter; MacDonald, A. M.; Strapp, J. Walter; McFarquhar, Greg
Measurements of HNO3 and NOy on Cirrus Ice Particles and in Solution Aerosols During CRYSTAL-FACE
NASA Astrophysics Data System (ADS)
NOx (NO + NO2) is central to tropospheric O3 production. The larger family of gases with which NOx interconverts, NOy, or total reactive nitrogen, includes HNO3. One potential mechanism for the removal and/or vertical transport of NOy is via uptake on ice particles and aerosols. NOx is unlikely to be subject to such uptake, and HNO3 is likely the most significant NOy species subject to uptake. Thus the uptake of HNO3 has the potential to affect indirectly the O3 budget of the atmospehre [Lawrence and Crutzen, Tellus, 1998; Meier and Hendricks, JGR, 2002]. To assess the degree of uptake, condensed-phase HNO3 and NOy were measured during CRYSTAL-FACE by instruments in adjacent pallets on the WB57. The instruments employed nearly identical inlets for the enhanced (anisokinetic) sampling of condensed-phase species. Each instrument employed a second inlet for the measurement of the gas-phase plus small-particle fraction. Differences in the small-particle sampling by these latter inlets has proven beneficial for the inference of condensed-phase HNO3 on particles with diameters of order 1 micron. This talk will emphasize the southern survey flight of 9 July 2002, for which we infer the presence of condensed-phase HNO3 in ternary solutions of H2O, H2SO4, and HNO3. Ice was found in greater and lesser amounts in the presence of the aerosols, but ice appears to have played little role in the uptake of HNO3 here, as the aerosols compete very effectively for the HNO3 in this particular case, due to the relatively large particle volume and the low temperatures. In addition, the condensed-phase NOy measurements are compared to the condensed-phase HNO3 measurements described in another presentation at this meeting (Popp et al.) Overall the condensed-phase HNO3 and NOy amounts are similar to one another and give no indication that other NOy species are taken up by cirrus ice particles.
Weinheimer, A. J.; Knapp, D. J.; Montzka, D. D.; Ridley, B. A.; Popp, P. J.; Gao, R. S.; Marcy, T. P.; Fahey, D. W.; Baumgardner, D.; Anderson, B. E.; Wilson, J. C.; Lee, S. H.; Reeves, J. M.; Lafleur, B. G.; Hilbert, H.; Schmit, O.; Herman, R. L.; Weinstock, E. M.; Smith, J. B.; Sayres, D. W.; Vellovic, J.; Anderson, J. G.; Bui, T. P.; Bowen, S. W.; Pfister, L.; Dean-Day, J.; Chang, C.
The Cloud Particle Spectrometer with Polarization Detection (CPSPD): A next generation open-path cloud probe for distinguishing liquid cloud droplets from ice crystals
NASA Astrophysics Data System (ADS)
The differentiation of small water droplets and ice crystals by in situ measurements, in the size range < 50 ?m, remains a challenge and the lack of such measurements is an obstacle to progress in understanding ice formation in clouds. A new microphysical instrument, the Cloud Particle Spectrometer with Polarization Detection (CPSPD), has been developed that measures light intensity scattered (in forward and backward directions) by individual cloud particles that pass through a focused laser beam and derives their size and thermodynamic phase (liquid or ice) in the optical diameter range from 2 to 50 ?m. The optical equivalent diameter is derived from the light scattered in the forward direction. The change in polarization state of the incident light, caused by interaction with the cloud particle, is determined from the polarized components of the backscattered light. The CPSPD, along with several other cloud microphysical probes, has been flown on the University of North Dakota Citation aircraft in mixed phase clouds. It has also been deployed and operated at the Zugspitze research station studying mountain clouds. The preliminary results show that liquid cloud droplets can be distinguished from ice crystals and that the ice fraction can be estimated; an important parameter for better understanding of cloud processes, particularly that of glaciation.
Baumgardner, Darrel; Newton, Roy; Kr�mer, Martina; Meyer, Jessica; Beyer, Alexander; Wendisch, Manfred; Vochezer, Paul
Crystallization and preliminary X-ray crystallographic analysis of an ice-binding protein (FfIBP) from Flavobacterium frigoris PS1.
Ice growth in a cold environment is fatal for polar organisms, not only because of the physical destruction of inner cell organelles but also because of the resulting chemical damage owing to processes such as osmotic shock. The properties of ice-binding proteins (IBPs), which include antifreeze proteins (AFPs), have been characterized and IBPs exhibit the ability to inhibit ice growth by binding to specific ice planes and lowering the freezing point. An ice-binding protein (FfIBP) from the Gram-negative bacterium Flavobacterium frigoris PS1, which was isolated from the Antarctic, has recently been overexpressed. Interestingly, the thermal hysteresis activity of FfIBP was approximately 2.5?K at 50?�M, which is ten times higher than that of the moderately active IBP from Arctic yeast (LeIBP). Although FfIBP closely resembles LeIBP in its amino-acid sequence, the antifreeze activity of FfIBP appears to be much greater than that of LeIBP. In an effort to understand the reason for this difference, an attempt was made to solve the crystal structure of FfIBP. Here, the crystallization and X-ray diffraction data of FfIBP are reported. FfIBP was crystallized using the hanging-drop vapour-diffusion method with 0.1?M sodium acetate pH 4.4 and 3?M sodium chloride as precipitant. A complete diffraction data set was collected to a resolution of 2.9?�. The crystal belonged to space group P4(1)22, with unit-cell parameters a = b = 69.4, c = 178.2?�. The asymmetric unit contained one monomer. PMID:22750870
Do, Hackwon; Lee, Jun Hyuck; Lee, Sung Gu; Kim, Hak Jun
NSDL National Science Digital Library
This animation starts with a schematic illustration of glacier growth and then introduces six different methods that researchers use when studying ice cores in order to deduce the climate of the past. The research methods that are briefly introduced are ice layering, pollen, oxygen isotopes, ice crystals and gases trapped inside, and other chemistry.
History, The A.
Crystal Distortion of Dy2Ti2O7 at the Spin Ice Transition Temperature
Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1/2. The Dy ions reside on the vertices of corner-linked tetrahedra. Due to a strong single-ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local <111> quantization axes. We measured the x-ray diffraction for a Dy2Ti2O7 powder sample between 0.15 K. and 20 K. The lattice spacing increases drastically between 1.5 K and about 1 K, with decreasing temperature. The lattice spacing of the (222) diffraction is considerably larger than the other directions.
Suzuki, H.; Hata, F.; Xue, Y.; Kaneko, H.; Hosomichi, A.; Abe, S. [Department of Physics, Kanazawa University, Kakuma-machi, Kanazawa 920-1192 (Japan); Higashinaka, R.; Nakatsuji, S.; Maeno, Y. [Department of Physics, Kyoto University, Kyoto 606-8502 (Japan)
Impulsive stimulated scattering in ice VI and ice VII
We demonstrate the use of forced thermal Brillouin scattering to obtain acoustic velocities for oriented high-pressure crystals of ice VI and of ice VII. The elastic constants of ice VI and ice VII determined from these measurements compare favorably with classical Brillouin scattering results.
Bruce J. Baer; J. M. Brown; Joseph M. Zaug; David Schiferl; Eric L. Chronister
Millimeter Wave Polarimetric Radar Remote Sensing of Ice Clouds
Ice clouds play important roles in many practical and theoretical researches. This thesis investigates the electromagnetic scattering properties of ice crystals at 94 and 220 GHz, and polarimetric radar techniques for ice crystal type discrimination and ice mass content estimation. The scattering amplitude matrix is computed for pristine ice crystals of different sizes and from different incidence directions using the
Chengxian Tang
NSDL National Science Digital Library
This is a lesson about the characteristics of ice as a mineral and how it compares to other minerals with respect to hardness. Learners will observe ice crystals, develop a hardness scale and position ice on it. Learners will also practice working collaboratively in a team. Activities include small group miming, speaking, drawing, and/or writing. This is lesson 3 of 12 in the unit, Exploring Ice in the Solar System.
Crystal shape-dependent magnetic susceptibility and Curie law crossover in the spin ices Dy2Ti2O7 and Ho2Ti2O7.
We present an experimental determination of the isothermal magnetic susceptibility of the spin ice materials Dy2Ti2O7 and Ho2Ti2O7 in the temperature range 1.8-300 K. The use of spherical crystals has allowed accurate correction for demagnetizing fields and allowed the true bulk isothermal susceptibility ?T(T) to be estimated. This has been compared against a theoretical expression based on a Husimi tree approximation to the spin ice model. Agreement between experiment and theory is excellent at T > 10 K, but systematic deviations occur below that temperature. Our results largely resolve an apparent disagreement between neutron scattering and bulk measurements that has been previously noted. They also show that the use of non-spherical crystals in magnetization studies of spin ice may introduce very significant systematic errors, although we note some interesting--and possibly new--systematics concerning the demagnetizing factor in cuboidal samples. Finally, our results show how experimental susceptibility measurements on spin ices may be used to extract the characteristic energy scale of the system and the corresponding chemical potential for emergent magnetic monopoles. PMID:23988470
Bovo, L; Jaubert, L D C; Holdsworth, P C W; Bramwell, S T
Crystal shape-dependent magnetic susceptibility and Curie law crossover in the spin ices Dy2Ti2O7 and Ho2Ti2O7
NASA Astrophysics Data System (ADS)
We present an experimental determination of the isothermal magnetic susceptibility of the spin ice materials Dy2Ti2O7 and Ho2Ti2O7 in the temperature range 1.8-300 K. The use of spherical crystals has allowed accurate correction for demagnetizing fields and allowed the true bulk isothermal susceptibility ?T(T) to be estimated. This has been compared against a theoretical expression based on a Husimi tree approximation to the spin ice model. Agreement between experiment and theory is excellent at T > 10 K, but systematic deviations occur below that temperature. Our results largely resolve an apparent disagreement between neutron scattering and bulk measurements that has been previously noted. They also show that the use of non-spherical crystals in magnetization studies of spin ice may introduce very significant systematic errors, although we note some interesting�and possibly new�systematics concerning the demagnetizing factor in cuboidal samples. Finally, our results show how experimental susceptibility measurements on spin ices may be used to extract the characteristic energy scale of the system and the corresponding chemical potential for emergent magnetic monopoles.
Bovo, L.; Jaubert, L. D. C.; Holdsworth, P. C. W.; Bramwell, S. T.
On the characterization of crystallization and ice adhesion on smooth and rough surfaces using molecular dynamics
NASA Astrophysics Data System (ADS)
Coarse-grained molecular dynamics is utilized to quantify the behavior of a supercooled water drop on smooth and rough surfaces. Crystallization on rough surface is characterized based on wetting states. Freezing temperature and work of adhesion of water droplet are linearly associated with roughness parameters corresponding to the Cassie-Baxter and Wenzel states. The behavior is insensitive to different surface-fluid affinity. We show in general, for Wenzel states, work of adhesion is higher than that of Cassie-Baxter state for surfaces that have identical freezing temperatures.
Singh, Jayant K.; M�ller-Plathe, Florian
Optimal numerical methods for determining the orientation averages of single-scattering properties of atmospheric ice crystals
NASA Astrophysics Data System (ADS)
The optimal orientation averaging scheme (regular lattice grid scheme or quasi Monte Carlo (QMC) method), the minimum number of orientations, and the corresponding computing time required to calculate the average single-scattering properties (i.e., asymmetry parameter (g), single-scattering albedo (?o), extinction efficiency (Qext), scattering efficiency (Qsca), absorption efficiency (Qabs), and scattering phase function at scattering angles of 90� (P11 (90�)), and 180� (P11 (180�))) within a predefined accuracy level (i.e., 1.0%) were determined for four different nonspherical atmospheric ice crystal models (Gaussian random sphere, droxtal, budding Bucky ball, and column) with maximum dimension D=10?m using the Amsterdam discrete dipole approximation at ?=0.55, 3.78, and 11.0?m.The QMC required fewer orientations and less computing time than the lattice grid. The calculations of P11 (90�) and P11 (180�) required more orientations than the calculations of integrated scattering properties (i.e., g, ?o, Qext, Qsca, and Qabs) regardless of the orientation average scheme. The fewest orientations were required for calculating g and ?o. The minimum number of orientations and the corresponding computing time for single-scattering calculations decreased with an increase of wavelength, whereas they increased with the surface-area ratio that defines particle nonsphericity.
Um, Junshik; McFarquhar, Greg M.
NSDL National Science Digital Library
This is a virtual journal article about polycrystalline ice. It focuses on plastic deformation, specific flow characteristics and crystallographic preferred orientations associated with polycrystalline ice within glaciers. Part I covers Polycrystalline aggregates deformed in pure-shear; Dynamic recrystallisation; Grain shape and preferred orientation change; Fabric; Evolution of glacial ice during deformation. Part II covers: Time lapse photography; Glaciers; Dislocations; Bernal-Fowler rule; Generation of defect structures; Crystal structure; Ice; Basal glide; Strain rate for glide on basal systems; Critical resolved shear stress; Non-basal glide; Diffusional flow; Plastic deformation; Primary creep; Secondary creep; Tertiary creep; Deformation maps; Grain growth; Grain size reduction; Anisotropic flow law for ice.
Wilson, Chris
Diffusion-controlled metabolism for long-term survival of single isolated microorganisms trapped within ice crystals
Two known habitats for microbial metabolism in ice are surfaces of mineral grains and liquid veins along three-grain boundaries. We propose a third, more general, habitat in which a microbe frozen in ice can metabolize by redox reactions with dissolved small molecules such as CO2, O2, N2, CO, and CH4 diffusing through the ice lattice. We show that there is an adequate supply of diffusing molecules throughout deep glacial ice to sustain metabolism for >105 yr. Using scanning fluorimetry to map proteins (a proxy for cells) and F420 (a proxy for methanogens) in ice cores, we find isolated spikes of fluorescence with intensity consistent with as few as one microbial cell in a volume of 0.16 ?l with the protein mapper and in 1.9 ?l with the methanogen mapper. With such precise localization, it should be possible to extract single cells for molecular identification.
Rohde, Robert A.; Price, P. Buford
Examining Crystal Fabric Develoment in Ice: Cryo EBSD, Deformation Experiments and the Link to En-glacial Reflectivity
NASA Astrophysics Data System (ADS)
Over the past few years, cryogenic electron back-scatter diffraction (Cryo-EBSD) has been increasingly used to examine micro-structures in both natural and experimentally deformed ice samples on a micron-scale. Experiments that investigate grain size-sensitive behavior require working on fine-grained ice. These samples present a number of experimental challenges. Issues that present particular difficulties include stable mounting of ice samples, transport of mounted samples and producing a planar, frost-free and damage-free surface. Recent work at the new Otago Ice Deformation Lab has led to the development of a number of experimental methods that help overcome these challenges and enable routine EBSD analysis of fine-grained ice. A brief outline of these experimental methods and some EBSD results from variably deformed ice samples will be presented. Shear deformation experiments on polycrystalline ice are being conducted in order to further explore the relationships between deformation, processes of recrystallization, and the development of anisotropic fabrics that lead to en-glacial seismic reflections. Self-contained, refrigerated deformation units fitted with digital controllers and hardware have been designed for unconfined deformation experiments on polycrystalline synthetic ice. Methods of analysis, from time-lapse photography to random-point tracking, are being employed for monitoring strain in real time. Various methods have been explored for monitoring the development of anisotropic fabrics in ice during progressive deformation. Ultra-sonic transducers can be used to monitor wave velocity changes in various orientations in materials under strain. These experiments have been designed with the objective of quantifying the relationship between deformation fabrics and en-glacial seismic reflectivity observed in thick grounded ice sheets.
Vaughan, Matthew; Prior, David; Seidemann, Meike; Gorman, Andrew; Lilly, Kat; Langhorne, Pat; Easingwood, Richard; Golding, Narayana; Durham, Bill
Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals - cloud chamber measurements in the context of contrail and cirrus microphysics
NASA Astrophysics Data System (ADS)
The article presents the laser scattering and depolarisation instrument SIMONE that is installed at the large aerosol and cloud chamber facility AIDA of the Karlsruhe Institute of Technology. SIMONE uses a 488 nm cw laser to probe simulated atmospheric clouds by measuring the scattered light from the 1.8� and 178.2� directions. At 178.2�, the scattered light is analysed for the linear polarisation state to deduce the particle linear depolarisation ratio ?p which is a common measurement parameter of atmospheric lidar applications. The optical setup and the mathematical formalism of the depolarisation detection concept are given. SIMONE depolarisation measurements in spheroidal hematite aerosol and supercooled liquid clouds are used to validate the instrument. SIMONE data from a series of AIDA ice nucleation experiments at temperatures between 195 and 225 K were analysed in terms of the impact of the ice particle microphysics on ?p. We found strong depolarisation values of up to 0.4 in case of small growing and sublimating ice particles with volume equivalent diameters of only a few micrometers. Modelling runs with the T-matrix method showed that the measured depolarisation ratios can be accurately reproduced assuming spheroidal and cylindrical particles with a size distribution that has been constrained by IR extinction spectroscopy. Based on the T-matrix modelling runs, we demonstrate that in case of small ice crystals the SIMONE depolarisation results are representative for the lidar depolarisation ratio which is measured at exact backscattering direction of 180�. The relevance of our results for the interpretation of recent lidar observations in cirrus and contrails is discussed. In view of our results, the high depolarisation ratios observed by the spaceborne lidar CALIOP in the tropical upper troposphere might be a hint for the presence of small (sublimating) ice particles in the outflows of deep convective systems.
Schnaiter, M.; B�ttner, S.; M�hler, O.; Skrotzki, J.; Vragel, M.; Wagner, R.
Influence of particle size and shape on the backscattering linear depolarisation ratio of small ice crystals - cloud chamber measurements in the context of contrail and cirrus microphysics
NASA Astrophysics Data System (ADS)
The article presents the laser scattering and depolarisation instrument SIMONE that is installed at the large aerosol and cloud chamber facility AIDA of the Karlsruhe Institute of Technology. SIMONE uses a 488 nm cw laser to probe simulated atmospheric clouds by measuring the scattered light from the 1.8� and 178.2� directions. At 178.2�, the scattered light is analysed for the linear polarisation state to deduce the linear depolarisation ratio ?l which is a common measurement parameter of atmospheric LIDAR applications. The optical setup and the mathematical formalism of the depolarisation detection concept are given. SIMONE depolarisation measurements in spheroidal hematite aerosol and supercooled liquid clouds are used to validate the instrument. SIMONE data from a series of AIDA ice nucleation experiments at temperatures between 195 and 225 K were analysed in terms of the impact of the ice particle microphysics on ?l. We found strong depolarisation values of up to 0.4 in case of small growing and sublimating ice particles with volume equivalent diameters of only a few micrometers. Modelling runs with the T-matrix method showed that the measured depolarisation ratios can be accurately reproduced assuming spheroidal and cylindrical particles with a size distribution that has been constrained by IR extinction spectroscopy. Based on the T-matrix modelling runs, we demonstrate that in case of small ice crystals the SIMONE depolarisation results are representative for the LIDAR depolarisation ratio which is measured at exact backscattering direction of 180�. The relevance of our results for the interpretation of recent LIDAR observations in cirrus and contrails is discussed. In view of our results, the high depolarisation ratios observed by the spaceborne LIDAR CALIOP in the tropical upper troposphere might be a hint for the presence of small (sublimating) ice particles in the outflows of deep convective systems.
Schnaiter, M.; B�ttner, S.; M�hler, O.; Skrotzki, J.; Vragel, M.; Wagner, R.
Recrystallization of ice in ice cream during controlled accelerated storage
Accelerated ice recrystallization in a thin film of vanilla ice cream was studied on a cold stage microscope, housed in a refrigerated glove box. Sample temperature was held constant (within �0.01 �C) or sinusoidally oscillated for 5 days. Changes in ice crystal size distribution were monitored using an image analysis technique. Several recrystallization mechanisms were observed. Melt-refreeze recrystallization was important
Daniel P. Donhowe; Richard W. Hartel
Dynamic Recrystallization of Ice in Polar Ice Sheets
The deformation and recrystallization mechanisms which control the viscoplasticity of ice from polar ice sheets have been investigated. The high plastic anisotropy of ice crystals is responsible for the development of a non uniform internal stress field within the polycrystal. Strain-shadows produced by sub-grain are observed in polarized light when the rotation recrystallization regime is dominant. Migration recrystallization occurs for
P. Duval; O. Castelnau
Ice Rheology Beyond Planet Earth
Barclay Kamb is well known for his seminal work on the motions and internal flow of glaciers, but he was also a pioneer in research on the crystal structures, chemical bonding, and rheologies of the high-pressure phases of ice. In the flow and fracture of terrestrial materials, no rock is more studied than ice. Water ice also has an important
W. B. Durham; S. H. Kirby; L. A. Stern
Crystallization of Gas-Laden Amorphous Water Ice, Activated by Heat Transport to its Subsurface Reservoirs, as Trigger of Huge Explosions of Comet 17P/Holmes
NASA Astrophysics Data System (ADS)
Thick terrain layers, of the type recognized on the Deep Impact mission's close-up images of the nucleus of comet 9P/Tempel, and each 10^(13) to 10^(14) grams in mass, are suggested to be attractive candidate carriers of solid material released into the atmosphere during super-massive explosions (megabursts) and/or major fragmentation events. The properties of the 2007 megaburst of comet 17P/Holmes are shown to be consistent with the triggering mechanism being a transformation of gas-laden water ice from low-density amorphous phase to cubic phase (crystallization) in a reservoir located beneath a layer tens of meters thick. Molecules of highly volatile gases, carbon monoxide in particular, trapped in amorphous water ice and released during the phase transition (at 130 K to 150 K), are superheated, generating -- almost instantly in a runaway process -- a momentum needed to lift off, from the comet's nucleus, the mass of the layer and, after its collapse, to accelerate the pile of mostly microscopic dust debris to subkilometer-per-second velocities. Strongly temperature dependent, the crystallization rate increases progressively between about 100 K at aphelion and nearly 120 K (with about 10 percent of the ice in cubic phase) some 10 days before the megaburst and explosively afterwards, due to the release of the trapped volatiles and completion of the phase transition. The proposed model is in agreement with a wide range of relevant observations of the 2007 megaburst of comet 17P, including the event's post-perihelion timing, the water production rate, the CO-to-H_2O production rate ratio, the dust halo's expansion rate, and the energy involved. The observed recurrence rate of super-massive explosions of comet 17P is explained by heat transport through the terrain layers whose effective thermal conductivity is about 0.2 W m^(-1) K^(-1).
Sekanina, Zdenek
NASA Astrophysics Data System (ADS)
We experimentally demonstrate that supersaturated solution of sodium acetate, commonly called �hot ice�, is a massively-parallel unconventional computer. In the hot ice computer data are represented by a spatial configuration of crystallization induction sites and physical obstacles immersed in the experimental container. Computation is implemented by propagation and interaction of growing crystals initiated at the data-sites. We discuss experimental prototypes of hot ice processors which compute planar Voronoi diagram, shortest collision-free paths and implement AND and OR logical gates.
Adamatzky, Andrew
Numerical Modeling of Ice Deposition
A method of computing the rate of growth of ice crystals by deposition is described. Predictions of growth characteristics over the temperature range of 1 through 35C are shown and compared with meager experimental data available within this temperature range.The growth rate equations are based on Fick's law of diffusion. In applying this law to nonspherical ice crystals, the analogy
L. R. Koenig
Impurity gradients in solution-grown ice and MgSO4�12H2O crystals measured by cryo-laser ablation and high-resolution-induced-coupled plasma mass spectrograph
NASA Astrophysics Data System (ADS)
During the eutectic freeze crystallization (EFC) of an industrial aqueous MgSO4 solution, ice and magnesium sulfate duodecahydrate ( MgSO4�12H2O(s)) were crystallized simultaneously near the eutectic point. It was found that the crystallization was highly selective: although the industrial feed solution contained appreciable levels of inorganic impurities (typically: 320 mg/L Cl-, 410 mg/L Ca2, 40 mg/L Mn, 70 mg/L Na+ and 50 mg/L K+), the formed ice and salt crystals contained lower levels of impurities (typically: 17 mg/L Cl-, 8 mg/L Ca, 17 mg/L Mn, and 5 mg/L Na). Also the ice was pure: only traces (typically: 20 mg/L SO42- and 5 mg/L Mg) of magnesium and sulfate were found in the ice crystals. In this work the spatial distribution of the impurities in the crystals is investigated. Gradients of composition in solids are measured by laser ablation high-resolution inductively coupled plasma mass spectrometry (LA-HR-ICP-MS). A special cryogenic sampling cell (<-80C) for laser ablation has been constructed. The focused (5- 10 ?m width) laser shoots at the frozen sample, scanning its surface. The vapor is fed to the mass spectrometer. In this way, the impurity concentration as a function of position in the crystal can be measured. The results of this method with MgSO4�12H2O and ice are presented.
G�rtner, R. S.; Genceli, F. E.; Trambitas, D. O.; Witkamp, G. J.
Optical spectra of orientationally disordered crystals. VI. The Raman spectrum of the translational lattice vibrations of ice Ih
The Raman spectrum of the translational vibrations of polycrystalline ice Ih has been investigated in the range 350-20 cm-1. All the vibrations are Raman active, and there is much fine structure, presumably due to particular points in the Brillouin zone. Tentative assignments are suggested for some of the features. The theory of the Raman scattering by the translational vibrations of
P. T. T. Wong; E. Whalley
Remote sensing estimates of cirrus particle size for tropical and midlatitude cirrus: Hexagonal crystals and ice spheres
NASA Technical Reports Server (NTRS)
A large discrepancy exists in current estimates of a mean cirrus particle size appropriate for calculations of the effects of these ice clouds on solar and thermal infrared radiative fluxes. For spheres with large size parameter (x = (2 pi r / lambda) is greater than 30, where r is particle radius), and moderate absorption (n(sup i) x less than 1, where n(sup i) is imaginary index of refraction for ice), the optimal effective particle radius is given by: r(sub e) = integral of r(exp 3)n(r)dr / integral of r(exp 2)n(r)dr. For the remote sensing of cirrus particle size at wavelengths of 0.83, 1.65, and 2.21 mu m, a 50 mu m ice sphere would have a size parameter of about 200, and values of n(sup i) x of 0, 0.045, and 0.06, satisfying the above conditions. However, while r(sub e) is a well-defined parameter for spheres, this cross-section area-weighted particle radius can only be extended to non-spherical particles by defining some equivalent sphere, typically an equivalent volume or equivalent cross-section area sphere. Using equivalent volume spheres, values of r(sub e) obtained over Lake Michigan on October 28, 1986, during FIRE phase I varied from 200 mu m (King Air 2D Imaging probes) to 60 mu m (Landsat reflectances at 0.83, 1.65, and 2.2 mu m), to 25 mu m (HIS spectrometer thermal emission between 8 and 12 mu m). Three major uncertainties were identified in this comparison: small ice particles missed by the 2D-C aircraft probes, uncertain ice refractive index, and uncertainties in the single scatter albedos and scattering phase functions used in the radiative calculations. Since the first FIRE cirrus results, advances have been made in all three areas. The present paper reports on improvements in the radiative modeling of ice particles at 0.83, 1.65, and 2.21 mu m wavelengths appropriate for comparisons to Landsat Thematic Mapper data. The paper also includes new results for Landsat observations of ice clouds in the eastern and western tropical Pacific.
Wielicki, Bruce A.; Minnis, Patrick; Arduini, Robert; Parker, Lindsay; Tsay, Si-Chee; Takano, Yoshihide; Liou, Kuo-Nan
NASA Technical Reports Server (NTRS)
Simmonds Precision's ice system consists of an ultrasonic sensor and a signal conditioner. The sensor has a piezoelectric ceramic crystal (PCC) that sends an ultrasonic pulse into an ice layer and detects an echo returning from the ice; the time elapsed in the pulse-echo round trip provides a basis for calculating ice thickness. Simmonds offers an alternative system with two PCCs, one a transmitter and the other a receiver for picking up the return echo. This technique offers detection of ice at much smaller thickness values, but at the cost of some ability to detect thicker ice. Among the advantages of the system are the small size of the sensor, which allows its placement in areas previously inaccessible. Other sensor advantages include high accuracy and insensitivity to salt spray, fog, chemicals and abrasion. Both sensor and signal conditioner offer high reliability, light weight and low power consumption.
Improved ice microphysics for numerical studies of ice fog using the Weather Research and Forecasting (WRF) model
NASA Astrophysics Data System (ADS)
An ice microphysics parameterization has been developed in order to better describe and understand ice fog formation. The modeling effort is based on observations in Interior Alaska, where ice fog occurs frequently during the cold season due strong inversions existing near the surface at extremely low air temperatures. The microphysical characteristics of ice fog are different from those of ice clouds, implying that ice microphysical processes should be corrected to generate the ice fog particles. Ice fog microphysical characteristics were derived with the NCAR Video Ice Particle Sampler (VIPS) during strong ice fog cases in the vicinity of Fairbanks, Alaska, in January and February 2012. The observational data were used to improve the ice nucleation parameterization, size distribution and gravitational settling in the Thompson scheme employed in the Weather Research and Forecasting (WRF) model. The new ice nucleation process generates the higher number concentration of ice crystals than the original Thompson scheme. The size distribution of ice crystals is changed into a Gamma distribution with the shape factor of 2.0, using the observed size distribution. Furthermore, gravitational settling is adjusted for the ice crystals to be suspended since the crystals in ice fog do not precipitate in similar manner when compared to the ice crystals of cirrus clouds. The slow terminal velocity plays a role in increasing the time scale for the ice crystal to take to settle to the surface. The sensitivity tests contribute to understanding the effects of water vapor emissions as an anthropogenic source on the formation of ice fog.
Kim, C.; Stuefer, M.; Schmitt, C. G.
Characterization of ice binding proteins from sea ice algae.
Several polar microalgae are able to live and thrive in the extreme environment found within sea ice, where growing ice crystals may cause mechanical damage to the cells and reduce the organisms' living space. Among the strategies adopted by these organisms to cope with the harsh conditions in their environment, ice binding proteins (IBPs) seem to play a key role and possibly contribute to their success in sea ice. IBPs have the ability to control ice crystal growth. In nature they are widespread among sea ice microalgae, and their mechanism of function is of interest for manifold potential applications. Here we describe methods for a classical determination of the IBP activity (thermal hysteresis, recrystallization inhibition) and further methods for protein characterization (ice pitting assay, determination of the nucleating temperature). PMID:24852640
Bayer-Giraldi, Maddalena; Jin, EonSeon; Wilson, Peter W
Measurements of HNO3 and NOy on Cirrus Ice Particles and in Solution Aerosols During CRYSTAL-FACE
NOx (NO + NO2) is central to tropospheric O3 production. The larger family of gases with which NOx interconverts, NOy, or total reactive nitrogen, includes HNO3. One potential mechanism for the removal and\\/or vertical transport of NOy is via uptake on ice particles and aerosols. NOx is unlikely to be subject to such uptake, and HNO3 is likely the most
A. J. Weinheimer; D. J. Knapp; D. D. Montzka; B. A. Ridley; P. J. Popp; R. S. Gao; T. P. Marcy; D. W. Fahey; D. Baumgardner; B. E. Anderson; J. C. Wilson; S. H. Lee; J. M. Reeves; B. G. Lafleur; H. Hilbert; O. Schmit; R. L. Herman; E. M. Weinstock; J. B. Smith; D. W. Sayres; J. Vellovic; J. G. Anderson; T. P. Bui; S. W. Bowen; L. Pfister; J. Dean-Day; C. Chang
Methods for Validation and Intercomparison of Remote Sensing and In situ Ice Water Measurements: Case Studies from CRYSTAL-FACE and Model Results
NASA Technical Reports Server (NTRS)
Remote sensing observations, such as those from AURA, are necessary to understand the role of cirrus in determining the radiative and humidity budgets of the upper troposphere. Using these measurements quantitatively requires comparisons with in situ measurements that have previously been validated. However, a direct comparison of remote and in situ measurements is difficult due to the requirement that the spatial and temporal overlap be sufficient in order to guarantee that both instruments are measuring the same air parcel. A difficult as this might be for gas phase intercomparisons, cloud inhomogeneities significantly exacerbate the problem for cloud ice water content measurements. The CRYSTAL-FACE mission provided an opportunity to assess how well such intercomparisons can be performed and to establish flight plans that will be necessary for validation of future satellite instruments. During CRYSTAL-FACE, remote and in situ instruments were placed on different aircraft (NASA's ER-2 and WB-59, and the two planes flew in tandem so that the in situ payload flew in the field of view of the remote instruments. We show here that, even with this type of careful flight planning, it is not always possible to guarantee that remote and in situ instruments are viewing the same air parcel. We use ice water data derived from the in situ Harvard Total Water (HV-TW) instrument, and the remote Goddard Cloud Radar System (CRS) and show that agreement between HV-TW and CRS is a strong function of the horizontal separation and the time delay between the aircraft transects. We also use a cloud model to simulate possible trajectories through a cloud and evaluate the use of statistical analysis in determining the agreement between the two instruments. This type of analysis should guide flight planning for future intercomparison efforts, whether for aircraft or satellite-borne instrumentation.
Sayres, D.S.; Pittman, J. V.; Smith, J. B.; Weinstock, E. M.; Anderson, J. G.; Heymsfield, G.; Li, L.; Fridlind, A.; Ackerman, A. S.
On the ice nucleation spectrum
NASA Astrophysics Data System (ADS)
This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.
Barahona, D.
On Understanding Stacking Fault Formation in Ice
NASA Astrophysics Data System (ADS)
Despite dedicated efforts aimed at revealing possible molecular structures of the ice defects associated with stacking faults in ice (I), these molecular arrangements have remained a puzzle. Here we demonstrate how the reorganization of water molecules on different faces of ice (I) can facilitate formation of stacking faults within a crystal. We show that a pair of point defects can manifest a particular combination of coupled five- and eight-membered rings (5-8 rings). These structural motifs can facilitate a shift in layers within an ice (I) crystal, thereby inducing stacking faults. Furthermore, the presence of molecular solutes such as methane at the ice interface appears to trigger the formation of coupled 5-8 rings. The observation of such coupled 5-8 ring defects provides insights into the possible molecular mechanisms of stacking fault formation in ice (I) and has implications for ice crystal growth phenomenology and the consequent physical and chemical properties of ice.
Pirzadeh, Payman; Kusalik, Peter G.
NASA Astrophysics Data System (ADS)
A Nd3+:Na2La4(WO4)7 crystal with dimensions of ? 17 � 30 mm3 was grown by the Czochralski method. The thermal expansion coefficients of Nd3+:Na2La4(WO4)7 crystal are 1.32 � 10-5 K-1 along c-axis and 1.23 � 10-5 K-1 along a-axis, respectively. The spectroscopic characteristics of Nd3+:Na2La4(WO4)7 crystal were investigated. The Judd-Ofelt theory was applied to calculate the spectral parameters. The absorption cross sections at 805 nm are 2.17 � 10-20 cm2 with a full width at half maximum (FWHM) of 15 nm for ?-polarization, and 2.29 � 10-20 cm2 with a FWHM of 14 nm for ?-polarization. The emission cross sections are 3.19 � 10-20 cm2 for ?-polarization and 2.67 � 10-20 cm2 for ?-polarization at 1,064 nm. The fluorescence quantum efficiency is 67 %. The quasi-cw laser of Nd3+:Na2La4(WO4)7 crystal was performed. The maximum output power is 80 mW. The slope efficiency is 7.12 %. The results suggest Nd3+:Na2La4(WO4)7 crystal as a promising laser crystal fit for laser diode pumping.
Yu, Yi; Huang, Yisheng; Zhang, Lizhen; Lin, Zhoubin; Sun, Shijia; Wang, Guofu
Ice/hydrohalite crystallization structures in sub-eutectic freezing experiments in the system NaCl-H20 and possible implications for the properties of frozen brines in Europa: A preliminary report
NASA Astrophysics Data System (ADS)
Sulfates are likely to be the most abundant solutes in the subsurface Europan liquid ocean. NaCl may also be a significant component of such liquids based on the compositions of stony meteorites like those thought to be among the source materials for the silicates in Europa's interior. The system NaCl-H20 exhibits a eutectic at -20.8�C and 23.3 weight percent NaCl between ice Ih and hydrohalite (NaCl.2H20). This low eutectic temperature compared to Mg and Na sulfate hydrate/ice eutectics indicates that hydrohalite should be among the last salts to crystallize in brine upwellings along rifts and other places where resurfacing by melt extrusion occurs on Europa. We conducted a suite of freezing experiments on NaCl brines with 20.3, 23.3, and 26.6 (saturated) weight percent NaCl by holding these liquids at a few degrees below the eutectic temperature. These runs produced ice-rich, eutectic and hydrohalite-rich aggregates of both phases, respectively, as confirmed by cryogenic x-ray diffraction and x-ray fluorescence spectroscopy. Based on direct observations of crystals forming at the tops and bottoms of the sample chambers and on refractive index measurements of subsequently melted sample material, marked fractional crystallization and segregation by density of ice, hydrohalite, and residual liquids occurred in the 20.3 and 26.6% samples and less so in for the eutectic composition. Crystallization of very fine grained eutectic intergrowths was recognized in cryogenic SEM images of all these samples and they were especially prominent in samples frozen from saturated brine. These samples were very difficult to cleave compared to pure polycrystalline ice, and hence are likely to have high fracture toughness. Direct measurements of this property and also the effects of partial melting on ductile flow rates are planned on such samples. Refracturing of such regions of fine eutectoid ice/hydrohalite intergrowths is likely to be inhibited in refrozen rifts compared to more ice-rich regions on Europa.
Rieck, K.; Kirby, S. H.; Stern, L. A.
Overview of Icing Research at NASA Glenn
NASA Technical Reports Server (NTRS)
The aviation industry continues to deal with icing-related incidents and accidents on a regular basis. Air traffic continues to increase, placing more aircraft in adverse icing conditions more frequently and for longer periods. Icing conditions once considered rare or of little consequence, such as super-cooled large droplet icing or high altitude ice crystals, have emerged as major concerns for modern aviation. Because of this, there is a need to better understand the atmospheric environment, the fundamental mechanisms and characteristics of ice growth, and the aerodynamic effects due to icing, as well as how best to protect these aircraft. The icing branch at NASA Glenn continues to develop icing simulation methods and engineering tools to address current aviation safety issues in airframe, engine and rotorcraft icing.
Kreeger, Richard E.
NSDL National Science Digital Library
This educational brief describes the nature and properties of the Greenland and Antarctica ice sheets. Topics include the thickness and aereal extent of the ice sheets, volume of water contained in them, mass balance, and the mechanisms by which ice is lost from or accumulated by the ice sheets.
Svalbard ice cores have not yet been fully exploited for studies of climate and environmental conditions. In one recently drilled ice core from Lomonosovfonna we have studied the methanesulphonic acid (MSA) records in relation to temperature and sea ice. During the present climatic conditions MSA appears to be negatively correlated with the sea ice conditions in the Barents Sea, and
Elisabeth Isaksson; Teija Kekonen; John Moore
NASA Astrophysics Data System (ADS)
The polarized absorption, emission spectra and decay time measurements of Pr3+-doped CaYAlO4 single crystal have been performed at room temperature. Based on the Judd-Ofelt theory, the spectroscopic parameters , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr3+:CaYAlO4 is a promising candidate for visible solid-state laser emission.
Lv, Shaozhen; Wang, Yan; Zhu, Zhaojie; You, Zhenyu; Li, Jianfu; Gao, Shufang; Wang, Hongyan; Tu, Chaoyang
NSDL National Science Digital Library
This site describes snow crystals and snowflakes. Although a common meteorological phenomenon, snow crystal growth is a fascinating and poorly understood process, in which remarkably complex and beautifully symmetric structures appear, quite literally, out of thin air. The many facets of snow crystals are described here, along with the attempts to understand their formation. Site highlights include research on creating designer snow crystals in the laboratory, the history of early snow crystal observations, snow crystal photography, properties of frozen precipitation, and a snow crystal primer for a short course in snow crystal physics - what snow crystals are, how they form, and why they form the way they do. Information is offered on snow crystal classification, preservation, and unusual crystal forms. An extensive image gallery of lab-created crystal forms is available, with enlargeable thumbnail images. There are even instructions for users on how to create crystals. This could be made into a classroom activity, as the science of the growth is explained. Snowflake Physics discusses diffusion, dendrite growth, ice surface physics, electric growth, and ice properties. A vast list of related links is also provided.
Libbrecht, Kenneth
Geomicrobiology of Vostok Ice: Implications for Life in Lake Vostok
NSDL National Science Digital Library
This abstract introduces newly discovered microbe assemblages within Lake Vostok and the research it has inspired. Current studies hope to gain insight into the following areas: physical stresses in deep glacial and accretion ice; the role of clathrates on gas dynamics within the lake; the origin of microbes in accretion ice; the physiological state of ice-bound microbes; the geochemistry of the ice column; and living microbes in ice veins that form at triple junctions in the ice crystal matrix.
Priscu, John
Chemical characterization of individual particles and residuals of cloud droplets and ice crystals collected on board research aircraft in the ISDAC 2008 study
NASA Astrophysics Data System (ADS)
Ambient particles and the dry residuals of mixed-phase cloud droplets and ice crystals were collected during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) near Barrow, Alaska, in spring of 2008. The collected particles were analyzed using Computer Controlled Scanning Electron Microscopy with Energy Dispersive X-ray analysis and Scanning Transmission X-ray Microscopy coupled with Near Edge X-ray Absorption Fine Structure spectroscopy to identify physico-chemical properties that differentiate cloud-nucleating particles from the total aerosol population. A wide range of individually mixed components was identified in the ambient particles and residuals including organic carbon compounds, inorganics, carbonates, and black carbon. Our results show that cloud droplet residuals differ from the ambient particles in both size and composition, suggesting that both properties may impact the cloud-nucleating ability of aerosols in mixed-phase clouds. The percentage of residual particles which contained carbonates (47%) was almost four times higher than those in ambient samples. Residual populations were also enhanced in sea salt and black carbon and reduced in organic compounds relative to the ambient particles. Further, our measurements suggest that chemical processing of aerosols may improve their cloud-nucleating ability. Comparison of results for various time periods within ISDAC suggests that the number and composition of cloud-nucleating particles over Alaska can be influenced by episodic events bringing aerosols from both the local vicinity and as far away as Siberia.
Hiranuma, N.; Brooks, S. D.; Moffet, R. C.; Glen, A.; Laskin, A.; Gilles, M. K.; Liu, P.; MacDonald, A. M.; Strapp, J. W.; McFarquhar, G. M.
Listen to this page Meth (Crank, Ice) Facts Methamphetamine�meth for short�is a white, bitter powder. Sometimes it's made into a white pill or ... clear or white shiny rock (called a crystal). Meth powder can be eaten or snorted up the ...
NASA Astrophysics Data System (ADS)
Single crystals of ice Ih, extracted from the subglacial Lake Vostok accretion ice layer (3621 m depth) were investigated by means of diffuse x-ray scattering and inelastic x-ray scattering. The diffuse scattering was identified as mainly inelastic and rationalized in the frame of ab initio calculations for the ordered ice XI approximant. Together with Monte-Carlo modelling, our data allowed reconsidering previously available neutron diffuse scattering data of heavy ice as the sum of thermal diffuse scattering and static disorder contribution.
Wehinger, Bj�rn; Chernyshov, Dmitry; Krisch, Michael; Bulat, Sergey; Ezhov, Victor; Bosak, Alexe�
Amorphous ice: density and reflectivity.
Amorphous ice prepared under a wide range of conditions has a density, determined from its buoyancy in liquid oxygen, of 0.94+/-0.02 gram per cubic centimeter, the same as that of ordinary hexagonal ice, with no indication of the glassy superdense ice (2.32 grams per cubic centimeter) reported recently. The diffuse reflectivity shows a small increase as the ice crystallizes at 153 degrees K. This increase is followed by a much larger increase (probably associated with crystal growth) as the sample warms, and the reflectivity reaches a maximum well below the melting temperature. Although the ice deposits appear translucent, the specular reflectivity is low, thus indicating a dull rather than a glassy surface. PMID:17737992
Ghormley, J A; Hochanadel, C J
Time-dependent behavior of different ice slurries during storage
One of the main advantages of ice slurry as secondary refrigerant is the possibility of cold storage, which enables load shifting and peak shaving. During cold storage, ice crystals are subject to mechanisms as attrition, agglomeration and Ostwald ripening causing changes in the crystal size distribution, which are of great importance for ice slurry systems since they influence other parameters
P. Pronk; T. M. Hansen; C. A. Infante Ferreira; G. J. Witkamp
Pack-Ice Studies in the Arctic Ocean
The annual stratification of pack ice has been examined. Summer layers are formed either by arrested growth or by thin layers of fresh-water ice. The crystal structure and the salt content of the ice reflect the seasonal cycle. During the growth of ice a pro- nounced orientation of crystalline structure develops; it is determined by vertical as well as by
W. Schwarzacher
Physics of Ice and Snow as Affects Thermal Pressure.
National Technical Information Service (NTIS)
The physics of ice affects the development and magnitude of thermal ice pressures on lakes and restricted areas of the sea. The crystal structure of ice, the structure of ice covers and snow are related to physical and mechanical properties. Properties ac...
L. Bergdahl
NASA Technical Reports Server (NTRS)
Sea ice covers vast areas of the polar oceans, with ice extent in the Northern Hemisphere ranging from approximately 7 x 10(exp 6) sq km in September to approximately 15 x 10(exp 6) sq km in March and ice extent in the Southern Hemisphere ranging from approximately 3 x 10(exp 6) sq km in February to approximately 18 x 10(exp 6) sq km in September. These ice covers have major impacts on the atmosphere, oceans, and ecosystems of the polar regions, and so as changes occur in them there are potential widespread consequences. Satellite data reveal considerable interannual variability in both polar sea ice covers, and many studies suggest possible connections between the ice and various oscillations within the climate system, such as the Arctic Oscillation, North Atlantic Oscillation, and Antarctic Oscillation, or Southern Annular Mode. Nonetheless, statistically significant long-term trends are also apparent, including overall trends of decreased ice coverage in the Arctic and increased ice coverage in the Antarctic from late 1978 through the end of 2003, with the Antarctic ice increases following marked decreases in the Antarctic ice during the 1970s. For a detailed picture of the seasonally varying ice cover at the start of the 21st century, this chapter includes ice concentration maps for each month of 2001 for both the Arctic and the Antarctic, as well as an overview of what the satellite record has revealed about the two polar ice covers from the 1970s through 2003.
Parkinson, Claire L.; Cavalieri, Donald J.
NSDL National Science Digital Library
This short video examines the recent melting ice shelves in the Antarctica Peninsula; the potential collapse of West Antarctic ice shelf; and how global sea levels, coastal cities, and beaches would be affected.
Geographic, National
Detection of snow and ice crystals using polarization radar measurements: comparison between ground-based in situ and S-Pol observations
NASA Astrophysics Data System (ADS)
Polarimetric radars have the potential of identifying 'bulk' hydrometeor types within the radar volume by, for example, combining various polarimetric observables. Semiempirical, rule-based hydrometeor identification algorithms have been developed for the linear polarimetric S-Pol radar of the National Center of Atmospheric Research (NCAR). S-Pol was deployed during the field phase of the Mesoscale Alpine Programme (MAP) in Northern Italy for 10 weeks during the fall of 1999. It was a key instrument for one specific objective of MAP, namely, the orographically induced heavy precipitation events at the southern slopes of the Alps. During MAP, two hydrometeor type identification algorithms were implemented for real-time display. While the algorithm developed at the University of Washington (UW) uses fixed boundaries in polarimetric space, the algorithm developed at NCAR uses a fuzzy logic approach. The performance of the algorithms was tested using ground-based in situ observations from a mountain station located 65 km from the radar. This observation included the use of Formvar replicas that preserve solid precipitation particles on a microscope slide, and optical spectrometer providing information on size spectra. In situ data of two case studies from MAP provided detailed information on snow and ice crystals and were therefore suitable for a comparison to radar-based hydrometeor type detection. Because of spatial and temporal differences in the observation, the comparison is discussed qualitatively. The algorithms are considered successful when a good qualitative correlation could be found between the evolution of the hydrometeor types observed by in situ measurements, and the evolution observed remotely. Results based on the NCAR algorithm consistently performed better than the UW algorithm in both cases.
Barthazy, Eszter; G�ke, Sabine; Vivekanandan, Jothiram; Ellis, Scott M.
Quasi-spherical compression of a spark-channel plasma
NASA Astrophysics Data System (ADS)
An axial spark channel in deuterium has been used as a target for implosive shock waves created with a conventional cylindrical theta-pinch device. The compression of the channel by the implosive waves raised the plasma electron temperature to approximately 120 eV for approximately 6 kJ of condenser bank energy and 1 torr initial gas pressure. In order to improve the efficiency of compression of the channel plasma and to reduce the end losses inherent in the cylindrical configuration, the theta-pinch geometry was then converted from cylindrical into spherical. Under identical conditions of gas pressure and condenser bank energy, the electron temperature now peaked at approximately 400 eV. When the bank energy was increased to approximately 10 kJ, neutron production was observed. The total neutron output per shot ranged from 100,000 to 1,000,000 and increased inversely with the pinch discharge volume.
Panarella, E.
Basal ice facies and supraglacial melt-out till of the Laurentide Ice Sheet, Tuktoyaktuk Coastlands, western Arctic Canada
NASA Astrophysics Data System (ADS)
Glacially-deformed massive ice and icy sediments (MI-IS) in the Eskimo Lakes Fingerlands and Summer Island area of the Tuktoyaktuk Coastlands, western Arctic Canada, show, in the same stratigraphic sequences, features characteristic of both basal glacier ice and intrasedimental ice. Basal-ice features comprise (1) ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in Alaska, Greenland and Iceland; (2) ice crystal fabrics similar to those from basal ice in Antarctica and ice-cored moraines on Axel Heiberg Island, Canada; and (3) a thaw or erosional unconformity along the top of the MI-IS, buried by glacigenic or aeolian sediments. Intrasedimental ice consists of pore ice and segregated ice formed within Pleistocene sands deposited before glacial overriding. The co-existence of basal and intrasedimental ice within the MI-IS records their occurrence within the basal ice layer of the Laurentide Ice Sheet. Stagnation of the ice sheet and melt-out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale. The widespread occurrence of supraglacial melt-out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost.
Murton, J. B.; Whiteman, C. A.; Waller, R. I.; Pollard, W. H.; Clark, I. D.; Dallimore, S. R.
Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.
New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf. PMID:17779616
Zotikov, I A; Zagorodnov, V S; Raikovsky, J V
NSDL National Science Digital Library
Monitor the temperature of a melting ice cube and use temperature probes to electronically plot the data on graphs. Investigate what temperature the ice is as it melts in addition to monitoring the temperature of liquid the ice is submerged in.
Consortium, The C.
Numerical investigation of heat transfer and pressure drop characteristics of tube�fin heat exchangers in ice slurry HVAC system
This paper analyzes the heat transfer and pressure drop characteristics of a tube�fin heat exchanger in ice slurry HVAC system. Ice slurry is a suspension of crystallized water based - ice solution with a freezing point depressant like ethylene glycol. The ice- slurry is pumpable, hence it is also called pumpable ice. The composition of ice slurry considered for analysis
S. Kalaiselvam; P. Karthik; S. Ranjit Prakash
Dynamically induced frustration as a route to a quantum spin ice state in Tb2Ti2O7 via virtual crystal field excitations and quantum many-body effects.
The Tb2Ti2O7 pyrochlore magnetic material is attracting much attention for its spin liquid state, failing to develop long-range order down to 50 mK despite a Curie-Weiss temperature thetaCW approximately -14 K. In this Letter we reinvestigate the theoretical description of this material by considering a quantum model of independent tetrahedra to describe its low-temperature properties. The naturally tuned proximity of this system near a N�el to spin ice phase boundary allows for a resurgence of quantum fluctuation effects that lead to an important renormalization of its effective low-energy spin Hamiltonian. As a result, Tb2Ti2O7 is argued to be a quantum spin ice. We put forward an experimental test of this proposal using neutron scattering on a single crystal. PMID:17501378
Molavian, Hamid R; Gingras, Michel J P; Canals, Benjamin
NASA Astrophysics Data System (ADS)
Pauling's model of hydrogen disorder in water ice represents the prototype of a frustrated system. Over the years it has spawned several analogous models, including Anderson's model antiferromagnet and the statistical "vertex" models. Spin Ice is a sixteen vertex model of "ferromagnetic frustration" that is approximated by real materials, most notably the rare earth pyrochlores Ho2Ti2O7, Dy2Ti2O7 and Ho2Sn2O7. These "spin ice materials" have the Pauling zero point entropy and in all respects represent almost ideal realisations of Pauling's model. They provide experimentalists with unprecedented access to a wide variety of novel magnetic states and phase transitions that are located in different regions of the field-temperature phase diagram. They afford theoreticians the opportunity to explore many new features of the magnetic interactions and statistical mechanics of frustrated systems. This chapter is a comprehensive review of the physics -- both experimental and theoretical -- of spin ice. It starts with a discussion of the historic problem of water ice and its relation to spin ice and other frustrated magnets. The properties of spin ice are then discussed in three sections that deal with the zero field spin ice state, the numerous field-induced states (including the recently identified "kagom� ice") and the magnetic dynamics. Some materials related to spin ice are briefly described and the chapter is concluded with a short summary of spin ice physics.
Bramwell, Steven T.; Gingras, Michel J. P.; Holdsworth, Peter C. W.
NASA Astrophysics Data System (ADS)
A novel combined interferometric-mask method for the formation of micro- and nanometric scale three-dimensional (3D) rotational symmetry quasi-crystalline refractive lattice structures in photorefractive materials is demonstrated experimentally. The method is based on micrometric scale spatial modulation of the light by amplitude mask in the radial directions and along the azimuthal angle and the use of counter-propagating beam geometry building up Gaussian standing wave, which defines the light modulation in the axial direction with half-wavelength periodicity. 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed 3D intensity distributions of the optical beams can be imparted into the photorefractive medium thus creating the micro- and sub-micrometric scale 3D refractive index volume lattices. The used optical scheme allows also the formation of 2D lattices by removing the back-reflecting mirror. 2D and 3D refractive lattices were recorded with the use of 532 nm laser beam and rotational symmetry mask in doped lithium niobate crystals and were tested by the probe beam far-field diffraction pattern imaging and direct observation by phase microscope. The formed rotational symmetry 3D refractive structures have the periods of 20-60 ?m in the radial directions, 60 ?m along the azimuthal angle and half-wavelength 266 nm in the axial direction.
Badalyan, A.; Hovsepyan, R.; Mantashyan, P.; Mekhitaryan, V.; Drampyan, R.
Frost flower formation on sea ice and lake ice
NASA Astrophysics Data System (ADS)
Frost flowers are clusters of ice crystals found on freshly formed sea ice and occasionally on frozen lakes. They belong to a class of vapour-related phenomena that includes freezing fog, hoar frost and dew. It has hitherto been supposed that they form by condensation from a supersaturated atmosphere or from water wicked up through porous sea ice. Here we show that they can form on solid, pure ice sublimating into an unsaturated atmosphere. We derive a general regime diagram showing the atmospheric conditions under which the different vapour-related phenomena occur and confirm our predictions of frost-flower formation with a series of laboratory experiments. Our results can be used in climate models to predict occurrence of frost flowers, which significantly enhance albedo and provide the substrate for chemical production of ozone-depleting bromine monoxide, and in paleo-climate reconstructions by relating observations of sea-salt aerosols in ice cores to atmospheric conditions.
Style, Robert W.; Worster, M. Grae
Ice Nuclei Variability and Ice Formation in Mixed-phase Clouds
NASA Astrophysics Data System (ADS)
While it is expected that ice nuclei impose a critical role in ice initiation in clouds, there are relatively few validations of direct relations between ice nuclei concentrations and ice crystal concentrations. Further, very little is known about the spatial and temporal distribution of ice nuclei, let alone their sources. Such knowledge is critical for understanding precipitation formation, cloud lifetimes, the existence of aircraft icing hazards, and the impacts of changing atmospheric aerosol particle concentrations and compositions on cold cloud processes. In this study, we document measurements of ice nuclei in relation to the presence and concentrations of ice crystals in modestly supercooled clouds and also consider the implications of differences in ice nuclei concentrations measured at different locations and times during several studies. In the first part of this presentation, we show results from measurements made in the Alliance Icing Research Study II, conducted in late Fall 2003 over the Northeast U.S. and Eastern Canada. A counterflow virtual impactor was used for selectively sampling cloud particles during aircraft measurements of clouds. Measurements were made on the evaporated residual aerosol particles, including re-processing at controlled temperatures and relative humidities to determine their ice nucleating behavior for conditions of direct relevance to the clouds using a continuous flow ice-thermal diffusion chamber (CFDC). Comparing to measurements of ice crystals in clouds, a clear correlation between the presence or absence of ice nuclei and ice crystals was demonstrated in some cases. However, the concentrations of the two populations did not correlate as well. Reasons for this may reflect different (or not assessed) ice formation processes, redistribution of ice in clouds, and potential artifacts of the sampling procedure. Since these results and those of Prenni et al. (this meeting), describing the vital role of ice nuclei in affecting Arctic cloud persistence and radiative properties, both support the critical impact of ice nuclei concentrations on mixed-phase cloud properties, we investigate climatological analyses of CFDC ice nuclei data collected at different locales and seasonally over the past several years. Aside from temperature and relative humidity control on ice nuclei concentrations, these analyses suggest regional and seasonal variability of ice nuclei concentrations, likely tied to meteorological control on transport of ice nuclei from sources (e.g., mineral dust) that may have direct implications on cold cloud processes.
Demott, P. J.; Twohy, C. H.; Prenni, A. J.; Kreidenweis, S. M.; Brooks, S. D.; Rogers, D. C.
Ice Nuclei Production in Volcanic Clouds
NASA Astrophysics Data System (ADS)
The paper [Durant et al., 2008] includes a review of research on ice nucleation in explosive volcanic clouds in addition to reporting their own research on laboratory measurements focused on single-particle ice nucleation. Their research as well as the research they reviewed were concerned with the freezing of supercooled water drops (250 to 260 K) by volcanic ash particles acting as ice freezing nuclei. Among their conclusions are: Fine volcanic ash particles are very efficient ice freezing nuclei. Volcanic clouds likely contain fine ash concentrations 104 to 105 times greater than found in meteorological clouds. This overabundance of ice nuclei will produce a cloud with many small ice crystals that will not grow larger as they do in meteorological clouds because the cloud water content is widely distributed among the numerous small ice crystals. The small ice crystals have a small fall velocity, thus volcanic clouds are very stable. The small ice crystals are easily lofted into the stratosphere transporting water and adsorbed trace gasses. In this paper we examine the mechanism for the production of the small ice nuclei and develop a simple model for calculating the size of the ice nuclei based upon the distribution of magma around imbedded bubbles. We also have acquired a volcanic bomb that exhibits bubble remnants on its entire surface. The naturally occurring fragments from the volcanic bomb reveal a size distribution consistent with that predicted by the simple model. Durant, A. J., R. A. Shaw, W. I. Rose, Y. Mi, and G. G. J. Ernst (2008), Ice nucleation and overseeding of ice in volcanic clouds, J. Geophys. Res., 113, D09206, doi:10.1029/2007JD009064.
Few, A. A.
NSDL National Science Digital Library
In this activity, learners experiment with the density of ice, water, and oil. Learners will discover that the density of a liquid determines whether it will float above or sink below another liquid. Learners will be surprised to find that ice floats and water sinks in oil, even though ice and water are made of the same thing. Learners will also examine the hydrophilic properties of water and the hydrophobic nature of oil.
Workshop, Mission S.
NASA Technical Reports Server (NTRS)
During 2013, Arctic sea ice extent remained well below normal, but the September 2013 minimum extent was substantially higher than the record-breaking minimum in 2012. Nonetheless, the minimum was still much lower than normal and the long-term trend Arctic September extent is -13.7 per decade relative to the 1981-2010 average. The less extreme conditions this year compared to 2012 were due to cooler temperatures and wind patterns that favored retention of ice through the summer. Sea ice thickness and volume remained near record-low levels, though indications are of slightly thicker ice compared to the record low of 2012.
Perovich, D.; Gerland, S.; Hendricks, S.; Meier, Walter N.; Nicolaus, M.; Richter-Menge, J.; Tschudi, M.
The Structure of Ice Nanoclusters: Implications for Interstellar Ice Grains
NASA Technical Reports Server (NTRS)
Crystalline ice nanoclusters and thin-films of pure and impure water ice were deposited and studied in order to evaluate the extent to which surface-related effects control bulk properties. In pure water ice nanoclusters and thin-films of impure water ice, the cubic to hexagonal phase transformation occurs at lower temperatures than in thin-film deposits of pure water ice. In laboratory-grown crystalline ice nanoclusters, approx. 20 nm diameter, a significant proportion of water molecules exists in surface and near-surface environments which have an amorphous or nearly amorphous character. These disordered regions, which are highly reactive, serve to promote transformations or reactions which would otherwise be kinetically hindered. Likewise, dilute impurities such as methanol, sequestered to the surface of thin-films on crystallization, introduce defects into the ice network, thereby allowing sluggish structural transitions to proceed. These structural effects, which are surface phenomena, are believed to play an important role in promoting molecular reactions known to occur within interstellar ice grains in cold molecular clouds, where the first organic compounds are formed.
Delzeit, L.; Blake, David; Uffindell, C.; DeVincenzi, Donald L. (Technical Monitor)
NSDL National Science Digital Library
To successfully model the climate, scientists need to know - among many things - how much ice there is at the poles. This radio broadcast reports on a new technique to measure the thickness of the ice by listening to it cracking and creaking. The clip is 2 minutes in length.
NSDL National Science Digital Library
This is a lesson about displacement, buoyancy, and density. Learners will understand why ice floats. Includes background information, teacher notes, assessment criteria, and related resources; activities are differentiated for Pre-K-grade 2 and grades 3-5. This is lesson 4 of the unit Exploring Ice in the Solar System.
Dust ice nuclei effects on cirrus clouds
NASA Astrophysics Data System (ADS)
In order to study aerosol-cloud interactions in cirrus clouds, we apply a new multiple-mode ice microphysical scheme to the general circulation model ECHAM5-HAM. The multiple-mode ice microphysical scheme allows for analysis of the competition between homogeneous freezing of solution droplets, deposition nucleation of pure dust particles, and immersion freezing of coated dust particles and pre-existing ice. We base the freezing efficiencies of coated and pure dust particles on the most recent laboratory data. The effect of pre-existing ice, which has been neglected in previous ice nucleation parameterizations, is to deplete water vapour by depositional growth and thus prevent homogeneous and heterogeneous freezing from occurring. As a first step, we extensively tested the model and validated the results against in situ measurements from various aircraft campaigns. The results compare well with observations; properties such as ice crystal size and number concentration as well as supersaturation are predicted within the observational spread. We find that heterogeneous nucleation on mineral dust particles and the consideration of pre-existing ice in the nucleation process may lead to significant effects: globally, ice crystal number and mass are reduced by 10 and 5%, whereas the ice crystals' size is increased by 3%. The reductions in ice crystal number are most pronounced in the tropics and mid-latitudes in the Northern Hemisphere. While changes in the microphysical and radiative properties of cirrus clouds in the tropics are mostly driven by considering pre-existing ice, changes in the northern hemispheric mid-latitudes mainly result from heterogeneous nucleation. The so-called negative Twomey effect in cirrus clouds is represented in ECHAM5-HAM. The net change in the radiation budget is -0.94 W m-2, implying that both heterogeneous nucleation on dust and pre-existing ice have the potential to modulate cirrus properties in climate simulations and thus should be considered in future studies.
Kuebbeler, M.; Lohmann, U.; Hendricks, J.; K�rcher, B.
Mass spectrometric measurements of the chemical composition of residuals from small ice crystals and from supercooled droplets in free tropospheric mixed phase clouds during CLACE 3 - 6
NASA Astrophysics Data System (ADS)
During the Cloud and Aerosol Characterization Experiments (CLACE 3 - 6) on the High Alpine Research Station Jungfraujoch (Switzerland, 3580 m asl) a novel Ice-CVI (Counterflow Virtual Impactor) was coupled to an Aerodyne Aerosol Mass Spectrometer (AMS), sampling and analyzing the non-refractory submicron particles. The measurements were performed in the late winter months of the years 2004, 2005, 2006, and 2007. A Q-AMS was operated in 2004 and 2005, while a HR-ToF-AMS was operated in 2006 and 2007. In 2006 and 2007, additionally a single particle laser ablation instrument (SPLAT) was employed. The combination of CVI and aerosol mass spectrometer allowed to analyze the residuals of ice nuclei as well as of supercooled cloud droplets, depending on cloud type and CVI operation mode. Within the same clouds, also interstitial aerosol was sampled and compared to the residual particles. Besides long episodes of free tropospheric aerosol, several cloud events were sampled, both within mixed-phase and pure supercooled clouds. The results show that the submicron aerosol in the free troposphere is composed to about 95% of non-refractive material, dominated by organic and sulfate aerosol. The ice cloud residuals sampled by the CVI show negligible mass concentration in the AMS compared to SMPS data, indicating that preferably refractory particles (mainly mineral dust and black carbon) act as ice nuclei. The HR-ToF-AMS data show a high contribution of oxygenated organic aerosol (OOA) in the free tropospheric background aerosol, confirming the assumption that photochemical aging converts primary organic aerosol emissions into oxygenated aerosol. The ice cloud residuals, in contrast, contain a small fraction of organic material that is dominated by hydrocarbon-like organic aerosol (HOA). This agrees with the finding that black carbon is also enriched in ice nuclei because HOA and black carbon have similar sources, mainly combustion processes.
Schneider, J.
Determining the ice-binding planes of antifreeze proteins by fluorescence-based ice plane affinity.
Antifreeze proteins (AFPs) are expressed in a variety of cold-hardy organisms to prevent or slow internal ice growth. AFPs bind to specific planes of ice through their ice-binding surfaces. Fluorescence-based ice plane affinity (FIPA) analysis is a modified technique used to determine the ice planes to which the AFPs bind. FIPA is based on the original ice-etching method for determining AFP-bound ice-planes. It produces clearer images in a shortened experimental time. In FIPA analysis, AFPs are fluorescently labeled with a chimeric tag or a covalent dye then slowly incorporated into a macroscopic single ice crystal, which has been preformed into a hemisphere and oriented to determine the a- and c-axes. The AFP-bound ice hemisphere is imaged under UV light to visualize AFP-bound planes using filters to block out nonspecific light. Fluorescent labeling of the AFPs allows real-time monitoring of AFP adsorption into ice. The labels have been found not to influence the planes to which AFPs bind. FIPA analysis also introduces the option to bind more than one differently tagged AFP on the same single ice crystal to help differentiate their binding planes. These applications of FIPA are helping to advance our understanding of how AFPs bind to ice to halt its growth and why many AFP-producing organisms express multiple AFP isoforms. PMID:24457629
Basu, Koli; Garnham, Christopher P; Nishimiya, Yoshiyuki; Tsuda, Sakae; Braslavsky, Ido; Davies, Peter
Extracellular macromolecules in sea-ice: Effects on sea-ice structure and their implications
NASA Astrophysics Data System (ADS)
Brine inclusions within sea-ice offer a favorable environment for certain marine microorganisms which live and thrive within the ice. These assemblages are a crucial element in the polar ecosystem. Partly entrained by ice platelets into the ice sheet, microorganisms closely interact with the liquid and solid phases of this porous environment (brine and ice), likely influencing their properties. Extracellular polysaccharide substances (EPS) and antifreeze proteins (AFP) have been identified as major elements with the potential to affect ice structure and processes, due to their capability to interact with ice crystals (selected planes in the case of AFPs) and with water molecules and salt ions present in the brine. EPS present in sea water can be selectively retained in the ice during ice formation, with implications for ice structure. Likewise, EPS and AFP released by sea-ice organisms would have a local effect, altering the microenvironment for the benefit of the organism. Macroscopic and microscopic observations showed effects on ice microstructure and a possible increase in brine fraction within the ice caused by AFPs and EPS, implicating changes in ice porosity and permeability. In the following we describe some of the interactions between sea-ice macromolecules, EPS and AFP, and the sea-ice system. We show their influence in ice structure, and discuss probable implications and consequences for microbial survival, distribution of dissolved material between sea-ice and the water column, and possible effects on the seasonal evolution of the ice. All of these could be relevant to the understanding of biogeochemical processes and the limits of habitability, as well as suggest possible applications of these substances.
Ewert, M.; Bayer-Giraldi, M.
Shape and size of contrails ice particles
A NASA DC-8, equipped as an in-situ sampling aircraft, flew in the exhaust wake of a Boeing 757 on May 4, 1996 over Kansas. Ice crystal samples were collected by impaction technique and replicated twice about 8 to 17 km behind the aircraft at an altitude of 11.8 km. The ice crystals in the contrail (after about 1 minute of
J. Goodman; R. F. Pueschel; E. J. Jensen; S. Verma; G. V. Ferry; S. D. Howard; S. A. Kinne; D. Baumgardner
NSDL National Science Digital Library
What's cooler than being cool? Setting ice on fire! In this demonstration, educators can amaze learners by setting ice on fire. Through this activity, learners can explore the properties of everyday materials and observe how these materials can change states to produce gas. Safety note: this activity is not suitable for learners to do themselves and should only be conducted by an experienced educator in a well ventilated lab area. Before doing this demonstration, educators should read the "Practicalities" section.
Museum, Science
[Spectral features analysis of sea ice in the Arctic Ocean].
Sea ice in the Arctic Ocean plays an important role in the global climate change, and its quick change and impact are the scientists' focus all over the world. The spectra of different kinds of sea ice were measured with portable ASD FieldSpec 3 spectrometer during the long-term ice station of the 4th Chinese national Arctic Expedition in 2010, and the spectral features were analyzed systematically. The results indicated that the reflectance of sea ice covered by snow is the highest one, naked sea ice the second, and melted sea ice the lowest. Peak and valley characteristics of spectrum curves of sea ice covered by thick snow, thin snow, wet snow and snow crystal are very significant, and the reflectance basically decreases with the wavelength increasing. The rules of reflectance change with wavelength of natural sea ice, white ice and blue ice are basically same, the reflectance of them is medium, and that of grey ice is far lower than natural sea ice, white ice and blue ice. It is very significant for scientific research to analyze the spectral features of sea ice in the Arctic Ocean and to implement the quantitative remote sensing of sea ice, and to further analyze its response to the global warming. PMID:22715789
Ke, Chang-qing; Xie, Hong-jie; Lei, Rui-bo; Li, Qun; Sun, Bo
Seismic anisotropy in ice: numerical modelling, ice core measurements and in-situ observations
NASA Astrophysics Data System (ADS)
The stress distribution and style of flow in ice produces elastic and rheological anisotropy, which informs ice flow modelling as to how ice masses respond to external changes such as global warming. Here observations of shear wave splitting from three-component icequake seismograms are used to characterise ice anisotropy in the Rutford ice stream, West Antarctica. Over 110 high quality measurements are made on 41 events recorded at five stations temporarily deployed near the ice stream grounding line. The magnitude of the splitting ranges from 2ms to 80ms and suggest a maximum of 6% shear wave splitting. The fast shear wave polarisation direction is roughly perpendicular to the ice flow direction. Motivated by these observations, we consider mechanisms for seismic anisotropy in ice using numerical modelling of the development of crystal preferred orientation of ice and measurement of crystal alignment in an ice core using electron back-scattered diffraction (EBSD). These results suggest transitions in the style of anisotropy both with depth and laterally within an ice stream. Seismic anisotropy is developed with increasing hydrostatic pressure producing a VTI fabric with a vertical alignment of c-axes (so-called cluster fabric). However, convergence in the ice flow and along-flow extension leads to girdles of c-axes (and an HTI fabric). Based on the Rutford shear-wave splitting observations we can rule out a cluster fabric as the sole cause of anisotropy - an HTI component is needed, which may be due extension in the direction of flow forming a girdle fabric or the alignment of cracks or ice-films in the plane perpendicular to the flow direction. Cumulatively, our observations suggest a combination of anisotropy mechanisms are at play in deforming ice sheets. We discuss seismic measurements that can be made to better discriminate between plausible mechanisms for our shear-wave splitting observations and how these different mechanisms may in turn alter ice flow and glacial response to external changes.
Kendall, J. M.; Baird, A. F.; Walker, A.; Wookey, J. M.; Lloyd, G. E.; Stuart, G. W.; Harland, S.; Obbard, R. W.; Smith, A.; Brisbourne, A.
The DC-8 Submillimeter-Wave Cloud Ice Radiometer
NASA Technical Reports Server (NTRS)
Submillimeter-wave cloud ice radiometry is an innovative technique for determining the amount of ice present in cirrus clouds, measuring median crystal size, and constraining crystal shape. The radiometer described in this poster is being developed to acquire data to validate radiometric retrievals of cloud ice at submillimeter wavelengths. The goal of this effort is to develop a technique to enable spaceborne characterization of cirrus, meeting key climate modeling and NASA measurement needs.
Walter, Steven; Batelaan, Paul; Siegel, Peter; Evans, K. Franklin; Evans, Aaron; Balachandra, Balu; Gannon, Jade; Guldalian, John; Raz, Guy; Shea, James; Smith, Christopher; Thomassen, John
Influence of a phase transition of ice on the heat and mass balance of comets
The effects of the presence of amorphous ice, crystallized at temperatures below 100 K, in comet nuclei on the heat and mass balance of comets are examined. The heat conduction coefficient of amorphous ice is estimated to be at least ten times lower than that of hexagonal ice above 20 K, with the amorphous ice coefficient increasing with temperature up
J. Klinger
Ice cloud microphysics, radiative transfer and large-scale cloud processes
Summary Parameterization programs for cloud microphyscs and radiative transfer involving ice clouds have been developed in terms of the mean effective size and ice water path. The mean effective size appears to be adequate in representing the ice crystal size distribution for radiative parameterizations. For a given ice water path, smaller mean effective sizes reflect more solar radiation, emit more
K. N. Liou; J. L. Lee; S. C. Ou; Q. Fu; Y. Takano
Deformation and folds of the basal ice under the Greenland ice sheet
NASA Astrophysics Data System (ADS)
Improvement of the depth sounding radio echo sounding over Greenland Ice Sheet has made it possible to map the near basal layers that have not been 'seen' earlier due to the very high demand of attenuation needed to reach through more than 3000m of ice. The basal 10% of the ice thickness reveals very disturbed layering in the central and north parts of the Greenland ice sheet. The onset of the disturbances very often seem to coincide with the ice from the climatic inception from the Eemian period to the Last Glacial period around 115.000 years before present. Studies of the ice rheology and deformation tests of the ice reveals big changes of ice crystal size and orientation at this boundary and very different deformation properties in the ice from the warm and cold climatic periods. Based on the different flow properties of the interglacial ice and the glacial ice models are used to simulate the formation of folds in ice.
Dahl-Jensen, Dorthe
Changes in the Antarctic Ice Sheet
NSDL National Science Digital Library
The Gulf of Maine Aquarium hosts this two-part activity. The focus is on seasonal changes in the mass balance of the Antarctic Ice Sheet. Part 1 uses an atlas and satellite imagery to examine the geography of the region and the changing boundaries of the ice sheet. Part 2 tracks annual changes in sea ice. There is an animation page showing changes in ice cover around Antarctica during 1991, and links to several other student activities: Coping with the Cold (Plan an expedition to Antarctica), Blubber Glove (Demonstrate how Antarctic animals stay warm in bone-chilling water), Salt Concentration (Demonstrate how cold-blooded animals survive subfreezing water temperatures without being shattered by ice crystals), Penguin Adaptation (Brainstorm ways in which penguins are well-adapted to cold water and icy environments), Chick Die-Off (Show how sea ice cover and penguin chick populations are related), and Creating Plankton (Design an ocean "wanderer").
A simulated Antarctic fast ice ecosystem
NASA Technical Reports Server (NTRS)
A 2D numerical ecosystem model of Antarctic land fast ice is developed to elucidate the primary production with the Antarctic sea ice zone. The physical component employs atmospheric data to simulate congelation ice growth, initial brine entrapment, desalination, and nutrient flux. The biological component is based on the concept of a maximum temperature-dependent algal growth rate which is reduced by limitations imposed from insufficient light or nutrients, as well as suboptimal salinity. Preliminary simulations indicate that, during a bloom, microalgae are able to maintain their vertical position relative to the lower congelation ice margin and are not incorporated into the crystal matrix as the ice sheet thickens. It is inferred that land fast sea ice contains numerous microhabitats that are functionally distinct based upon the unique set of processes that control microalgal growth and accumulation within each.
Arrigo, Kevin R.; Kremer, James N.; Sullivan, Cornelius W.
NASA Technical Reports Server (NTRS)
Tomco Equipment Company has participated in the dry ice (solid carbon dioxide, CO2) cleaning industry for over ten years as a pioneer in the manufacturer of high density, dry ice cleaning pellet production equipment. For over four years Tomco high density pelletizers have been available to the dry ice cleaning industry. Approximately one year ago Tomco introduced the DI-250, a new dry ice blast unit making Tomco a single source supplier for sublimable media, particle blast, cleaning systems. This new blast unit is an all pneumatic, single discharge hose device. It meters the insertion of 1/8 inch diameter (or smaller), high density, dry ice pellets into a high pressure, propellant gas stream. The dry ice and propellant streams are controlled and mixed from the blast cabinet. From there the mixture is transported to the nozzle where the pellets are accelerated to an appropriate blasting velocity. When directed to impact upon a target area, these dry ice pellets have sufficient energy to effectively remove most surface coatings through dry, abrasive contact. The meta-stable, dry ice pellets used for CO2 cleaning, while labeled 'high density,' are less dense than alternate, abrasive, particle blast media. In addition, after contacting the target surface, they return to their equilibrium condition: a superheated gas state. Most currently used grit blasting media are silicon dioxide based, which possess a sharp tetrahedral molecular structure. Silicon dioxide crystal structures will always produce smaller sharp-edged replicas of the original crystal upon fracture. Larger, softer dry ice pellets do not share the same sharp-edged crystalline structures as their non-sublimable counterparts when broken. In fact, upon contact with the target surface, dry ice pellets will plastically deform and break apart. As such, dry ice cleaning is less harmful to sensitive substrates, workers and the environment than chemical or abrasive cleaning systems. Dry ice cleaning system components include: a dry ice pellet supply, a non-reactive propellant gas source, a pellet and propellant metering device, and a media transport and acceleration hose and nozzle arrangement. Dry ice cleaning system operating parameters include: choice of propellant gas, its pressure and temperature, dry ice mass flow rate, dry ice pellet size and shape, and acceleration nozzle configuration. These parameters may be modified to fit different applications. The growth of the dry ice cleaning industry will depend upon timely data acquisition of the effects that independent changes in these parameters have on cleaning rates, with respect to different surface coating and substrate combinations. With this data, optimization of cleaning rates for particular applications will be possible. The analysis of the applicable range of modulation of these parameters, within system component mechanical constraints, has just begun.
Barnett, Donald M.
High density amorphous ice at room temperature
The phase diagram of water is both unusual and complex, exhibiting a wide range of polymorphs including proton-ordered or disordered forms. In addition, a variety of stable and metastable forms are observed. The richness of H2O phases attests the versatility of hydrogen-bonded network structures that include kinetically stable amorphous ices. Information of the amorphous solids, however, is rarely available especially for the stability field and transformation dynamics�but all reported to exist below the crystallization temperature of approximately 150�170�K below 4�5�GPa. Here, we present the evidence of high density amorphous (HDA) ice formed well above the crystallization temperature at 1�GPa�well inside the so-called �no-man�s land.� It is formed from metastable ice VII in the stability field of ice VI under rapid compression using dynamic-diamond anvil cell (d-DAC) and results from structural similarities between HDA and ice VII. The formation follows an interfacial growth mechanism unlike the melting process. Nevertheless, the occurrence of HDA along the extrapolated melt line of ice VII resembles the ice Ih-to-HDA transition, indicating that structural instabilities of parent ice VII and Ih drive the pressure-induced amorphization.
Chen, Jing-Yin; Yoo, Choong-Shik
De-icing: recovery of diffraction intensities in the presence of ice rings.
Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality. PMID:20516627
Chapman, Michael S; Somasundaram, Thayumanasamy
De-icing: recovery of diffraction intensities in the presence of ice rings
Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality.
Chapman, Michael S.; Somasundaram, Thayumanasamy
Geophysical observations of polar ice sheets and ice shelves
NASA Astrophysics Data System (ADS)
Knowledge of processes, dynamics, and the ongoing mass-balance of polar ice sheets is essential if we are to understand the response of the cryosphere to a changing climate. Here we present a series of hypotheses and associated observations and interpretations addressing the West Antarctic and Greenland ice sheets. Specific attention is paid to the grounding line, ice-shelf mass balance, and crystal orientation fabrics in streaming ice. Initially, GLAS ICESat laser altimetry data is used in an accurate and rapid method of grounding line location. The method exploits the high surface-slope at the grounding line relative to the at ice-shelf and ice streams. Validation is performed using ground-based observations and comparisons between the modern grounding-line and past estimates indicate that the Siple Coast grounding line has been largely static for at least several decades. During this time the ice streams have been undergoing large changes in flow speed indicating that the grounding-line position is insensitive to such changes. In order to address the mass balance of the Ross Ice Shelf, a divergence method assuming steady-state is used to estimate the spatial distribution and magnitude of basal melting (M?b). An area-average rate of -0.08+/-.01 m a--1 is estimated indicating that accretion dominates the sub-ice-shelf environment with rates of M?b=-0.32+/-0.01 m a--1 estimated in the centre of the ice shelf. Our estimates of accretion are an order of magnitude higher than previous studies and we caution that this is likely due to the divergence method misinterpreting past non-steady-state behavior of the ice streams. High melt rates (1.3+/-0.1 m a--1) are observed at the ice shelf front. The ice front is further investigated using spatial and temporal elevation changes from GLAS ICESat laser altimetry data. Melt rates are observed to increase exponentially as the front is approached, from zero at approximately 40 km from the front to an average of 2.7+/-0.9 m a--1 within the front kilometer. Melt estimates are best fit by the relationship M? b=2.1ex/11800 m a--1. Melt at the front is modeled as a combination of tidally-induced mixing and the ascension of buoyant water from beneath the ice shelf, indicating a relationship between melt profile and calving history. In the final section of this study, active-source seismic data are reported from an upstream location on Greenland's fastest-flowing outlet glacier, Jakobshavn Isbrae. Englacial reflectivity in these data reveal the development of complex and alternating crystal orientation fabrics, which we associate with changes in impurity loading brought about by climactic changes. These fabrics likely result in strain localization and therefore have implications for predictive ice sheet modeling.
Horgan, Huw J.
Predominance of Homogeneous Ice nucleation during the Formation of Cirrus Clouds
NASA Astrophysics Data System (ADS)
Cirrus cloud formation proceeds either by homogeneous freezing (HOM) of liquid droplets or by heterogeneous ice nucleation (HET) on ice nuclei. Liquid droplets are ubiquitous in the upper troposphere and HOM is commonly associated with high concentrations of ice crystals. On the other hand ice nuclei are very scarce in the upper troposphere and cirrus clouds produced by HET tend to have low ice crystal concentration. Recent studies have suggested that observed ice crystal concentration in cirrus is more consistent with a HET scenario than with cirrus clouds formed by HOM. Here we revised such picture and show that although heterogeneous ice nucleation has a significant influence on cirrus formation, when considered over a global basis homogeneous ice nucleation is the predominant mechanism of ice formation. Modeling experiments were carried out with NASA Global Observing System (GEOS). The ice nucleation parameterization in GEOS has been updated to account for the effect of competition between HOM and HET mechanisms, water vapor deposition onto preexisting ice crystals, and parcel history during cirrus cloud formation. When these factors are considered, the ice crystal concentration produced by HOM and HET become comparable. Moreover, over extended areas in the West coast of North and South America, as well as Central Asia HET becomes the predominant path of the ice crystal production. These regions are typically the focus of field campaigns and this may explain the predominance of heterogeneous ice nucleation observed in collected ice crystal residuals. However over the rest of the world, and particularly over most of the Southern Hemisphere, ice crystal production is dominated by HOM. This picture reconciles model results and field campaign observations.
Barahona, Donifan
Forecasting Aviation Icing: Icing Type and Severity
NSDL National Science Digital Library
This Web-based module presents the various types and severity categories of aircraft icing and outlines the main factors, physical processes, and mesoscale environments that combine to create hazardous icing conditions. The module also includes recent research findings in the area of supercooled large drop (SLD) clear icing and a supplementary section with forecast methods for diagnosing and predicting SLD clear icing conditions.
Forecasting Aviation Icing: Icing Type and Severity
NSDL National Science Digital Library
This Web-based module presents the various types and severity categories of aircraft icing and outlines the main factors, physical processes, and mesoscale environments that combine to create hazardous icing conditions. The module also includes recent research findings in the area of supercooled large drop (SLD) clear icing and a supplementary section with forecast methods for diagnosing and predicting SLD clear icing conditions.
Spangler, Tim
H2O will be more resistant to metallization than previously thought. From computational evolutionary structure searches, we find a sequence of new stable and meta-stable structures for the ground state of ice in the 1�5�TPa (10 to 50�Mbar) regime, in the static approximation. The previously proposed Pbcm structure is superseded by a Pmc21 phase at p�=�930�GPa, followed by a predicted transition to a P21 crystal structure at p�=�1.3�TPa. This phase, featuring higher coordination at O and H, is stable over a wide pressure range, reaching 4.8�TPa. We analyze carefully the geometrical changes in the calculated structures, especially the buckling at the H in O-H-O motifs. All structures are insulating�chemistry burns a deep and (with pressure increase) lasting hole in the density of states near the highest occupied electronic levels of what might be component metallic lattices. Metallization of ice in our calculations occurs only near 4.8�TPa, where the metallic C2/m phase becomes most stable. In this regime, zero-point energies much larger than typical enthalpy differences suggest possible melting of the H sublattice, or even the entire crystal.
Hermann, Andreas; Ashcroft, N. W.; Hoffmann, Roald
Sea ice - Multiyear cycles and white ice
NASA Technical Reports Server (NTRS)
The multiyear thickness cycles represent one of the interesting features of the sea ice studies performed by Semtner (1976) and Washington et al. (1976) with simple thermodynamic models of sea ice. In the present article, a description is given of results which show that the insulating effect of snow on the surface of the sea ice is important in producing these multiyear cycles given the physics included in the model. However, when the formation of white ice is included, the cycles almost disappear. White ice is the ice which forms at the snow-ice interface when the snow layer becomes thick enough to depress the ice below the water level. Water infiltrates the snow by coming through the ice at leads and generally freezes there, forming white ice.
Ledley, T. S.
A modeling study of ice formation affected by aerosols
NASA Astrophysics Data System (ADS)
This study investigates the effects of cloud condensation nuclei (CCN) and ice nuclei (IN) on ice formation in mixed-phase clouds using an adiabatic parcel model. The simulations with lower updrafts represent mixed-phase stratiform clouds, and those with higher updrafts represent deep convective clouds. Increasing CCN concentration can lead to more ice crystals with smaller sizes, but does not affect the height of freezing nucleation at lower updrafts. At higher updrafts, ice number concentration is more sensitive to CCN, and CCN effect on ice nucleation height is also more noticeable. This study also investigates the effects of IN properties (number concentration, size, contact angle) on ice formation assuming the immersion freezing mechanism. At very low IN number concentration, ice nucleation is dominated by homogeneous freezing and ice number concentration is relatively high. As IN number concentration is increased, ice number concentration decreases because both heterogeneous and homogeneous freezing processes occur. A mixed-phase layer extends up to the height for homogeneous freezing and there is a competition between the two freezing processes. As IN number concentration is further increased, ice number concentration increases because heterogeneous freezing dominates ice nucleation. IN number concentration needs to be higher for heterogeneous freezing to dominate ice nucleation at higher updrafts and lower at lower updrafts. Increasing IN size and contact coefficient also increases the contribution of heterogeneous freezing to ice nucleation. Finally, spheroids are used to represent columnar and plate-like ice crystals. CCN and IN effects are not dependent on the assumption of ice crystal shapes.
Li, Zhe; Xue, Huiwen; Yang, Fan
Forces Generated by High Velocity Impact of Ice on a Rigid Structure
NASA Technical Reports Server (NTRS)
Tests were conducted to measure the impact forces generated by cylindrical ice projectiles striking a relatively rigid target. Two types of ice projectiles were used, solid clear ice and lower density fabricated ice. Three forms of solid clear ice were tested: single crystal, poly-crystal, and "rejected" poly-crystal (poly-crystal ice in which defects were detected during inspection.) The solid ice had a density of approximately 56 lb/cu ft (0.9 gm/cu cm). A second set of test specimens, termed "low density ice" was manufactured by molding shaved ice into a cylindrical die to produce ice with a density of approximately 40 lb/cu ft (0.65 gm/cu cm). Both the static mechanical characteristics and the crystalline structure of the ice were found to have little effect on the observed transient response. The impact forces generated by low density ice projectiles, which had very low mechanical strength, were comparable to those of full density solid ice. This supports the hypothesis that at a velocity significantly greater than that required to produce fracture in the ice, the mechanical properties become relatively insignificant, and the impact forces are governed by the shape and mass of the projectile.
Pereira, J. Michael; Padula, Santo A., II; Revilock, Duane M.; Melis, Matthew E.
Parameterizing Size Distribution in Ice Clouds
PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 �m) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 �m), known as the �small mode�. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice cloud optical properties formulated in terms of PSD parameters in combination with remote measurements of thermal radiances to characterize the small mode. This is possible since the absorption efficiency (Qabs) of small mode crystals is larger at 12 �m wavelength relative to 11 �m wavelength due to the process of wave resonance or photon tunneling more active at 12 �m. This makes the 12/11 �m absorption optical depth ratio (or equivalently the 12/11 �m Qabs ratio) a means for detecting the relative concentration of small ice particles in cirrus. Using this principle, this project tested and developed PSD schemes that can help characterize cirrus clouds at each of the three ARM sites: SGP, NSA and TWP. This was the main effort of this project. These PSD schemes and ice sedimentation velocities predicted from them have been used to test the new cirrus microphysics parameterization in the GCM known as the Community Climate Systems Model (CCSM) as part of an ongoing collaboration with NCAR. Regarding the second problem, we developed and did preliminary testing on a passive thermal method for retrieving the total water path (TWP) of Arctic mixed phase clouds where TWPs are often in the range of 20 to 130 g m-2 (difficult for microwave radiometers to accurately measure). We also developed a new radar method for retrieving the cloud ice water content (IWC), which can be vertically integrated to yield the ice water path (IWP). These techniques were combined to determine the IWP and liquid water path (LWP) in Arctic clouds, and hence the fraction of ice and liquid water. We have tested this approach using a case study from the ARM field campaign called M-PACE (Mixed-Phase Arctic Cloud Experiment). This research led to a new satellite remote sensing method that appears promising for detecting low levels of liquid water in high clouds typically between -20 and -36 oC. We hope to develop this method in future research.
DeSlover, Daniel; Mitchell, David L.
Heterogeneous Ice Nuclei Measurements in Monte Cimone, Italy
NASA Astrophysics Data System (ADS)
Supercooled liquid droplets may coexist with ice crystals below the freezing point in mixed phase clouds. Although pure liquid droplets will not freeze spontaneously until the homogeneous freezing temperature -38�C, ice crystals exist at warmer temperatures due to the presence of ice nuclei (IN), that allow heterogeneous freezing on their surface. Only a small portion of the natural and anthropogenic aerosols serve as ice nuclei. Each aerosol type has its own ability to create and grow ice. IN ability varies with chemical and physical properties and with the environmental characteristics, as temperature and humidity. In this study, samples of aerosol particles were collected on a daily basis over a period of two weeks, on top of Monte Cimone in Italy (44.18�N, 10.70�E, 2165m asl), as part of the PEGASOS (Pan-European Gas-AeroSOl-climate interaction Study) project. The aerosols precipitated electrostatically onto a silicon wafer for an offline measurement of the ice nucleation ability, using the FRankfurt Ice Nuclei Deposition FreezinG Experiment (FRIDGE). The FRIDGE is a vacuum diffusion chamber that generates the sub-freezing temperatures and the supersaturations above ice, simulating conditions that exist inside a mixed phase cloud. On top of the chamber, a camera monitors the formation of ice crystals and a new counting algorithm reports the number concentration of ice crystals. During this campaign, a Saharan dust storm reached the sampling area and the ice nuclei concentrations were higher compared to the daily ice nuclei concentrations for the rest of the campaign. This result supports the previous findings that dust particles are among the most effective and important natural sources of ice nuclei.
Rudich, Y.; Reicher, N.; Schrod, J.; Bingemer, H. G.
Observing CMB polarisation through ice
Ice crystal clouds in the upper troposphere can generate polarisation signals\\u000aat the uK level. This signal can seriously affect very sensitive ground based\\u000asearches for E- and B-mode of Cosmic Microwave Background polarisation. In this\\u000apaper we estimate this effect within the ClOVER experiment observing bands (97,\\u000a150 and 220 GHz) for the selected observing site (Llano de Chajnantor,
Luca Pietranera; Stefan A. Buehler; Paolo G. Calisse; Claudia Emde; Darren Hayton; Viju Oommen John; Bruno Maei; Lucio Piccirillo; Giampaolo Pisano; Giorgio Savini; T. R. Sreerekha
Phase Transformation and Intense 2.7 ?m Emission from Er3+ Doped YF3/YOF Submicron-crystals
Yttrium fluoride YF3:Er3+ and yttrium oxyfluoride YOF:Er3+ submicron-crystals with mid-infrared fluorescent emissions were synthesized for the first time. The rhombohedral phase YOF submicron-crystals were synthesized by the crystalline phase transformation from pure orthorhombic YF3 submicron-crystals, which were prepared by co-precipitation method. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM), which showed that submicron-crystals were quasi-spherical with the particle size of ~400?nm. A novel formation mechanism of YOF submicron-crystals was proposed. Photoluminescence (PL) spectra indicated the 2.7??m emission of Er3+ has remarkably enhanced with the increase of Er3+ doping concentration, and a novel dynamic circulatory energy transfer mechanism was proposed. Fourier transform infrared spectra (FTIR) were used to demonstrate the change of hydroxyl content. These oxyfluoride submicron-crystals provide a new material for nano/submicron-crystals-glass composites, and open a brand new field for the realization of mid-infrared micro/nano-lasers.
Chai, Guanqi; Dong, Guoping; Qiu, Jianrong; Zhang, Qinyuan; Yang, Zhongmin
NSDL National Science Digital Library
In this activity, students will explore the characteristics of ice and explain the influencing factors by using Internet connections to polar field experiences, making their own ice cores and taking a field trip for obtaining a local ice core. The students will practice scientific journaling to document their observations. They will assemble their findings, develop a poster of their ice core and explain their observations. The 'ice is ice' misconception will be dispelled. Students will explain what scientists learn from ice cores and define basic vocabulary associated with ice cores.
Kolb, Sandra
About the role of ice in the reconstruction of ice
NASA Astrophysics Data System (ADS)
As part of the Molecules and Interstellar Ices project, we report the first theoretical results obtained on one of the possible mechanisms for the reconstruction of the ice mantle of interstellar grains after irradiation by the radiation field. In the ISM, the growth of the ice mantle is assumed to proceed more by radical recombination O + H + H than by direct condensation on the grain (Kouchi et al. A&A 1994). Due to the extremely small probability of finding these three species on the same site simultaneously, water formation is thought to be a two-step process: H + O ? OH (1) OH + H ? H2O (2a) Another mechanism has recently been found to operate in the cryogenic environments of noble gas matrices (Krim et al. in preparation) OH + OH ? H2O + O (2b) and the O:H2O complex has been characterized by FTIR spectroscopy. Reaction (2b) opens a new scenario that could be effective in the reconstruction of the ice by using the same OH radicals formed by the irradiation. Here we present a theoretical study of reaction (2b) in a model environment - in the presence of an increasing number of water molecules (DFT ; MP2 ; CCSD ; CCSD(T)) - in the presence of an ice surface extracted from the ice crystal (DFT) - in the presence of an ordered and periodic crystalline surface (periodic DFT/VASP) The first study performed in the gas phase shows that the reaction is exothermic (?H�16 kcal/mol) with an activation barrier (?E�2 kcal/mol) in such condition. In a second step, the OH + OH reaction is studied, taking into account the interaction of all species with the ice surface along the whole reaction path; The characteristic points on the potential energy surface, including adsorption sites and transition states, have been determined for each situation. It is found that the activation barrier vanishes as soon as an aggregate of three water molecules or more represents the surface. In addition to the formation of H2O, reaction (2b) provides atomic oxygen ready to take a hydrogen atom to form another OH radical to restart the process. The ice mantle could then be reformed by in situ recombination. Our results suggest also that the OH radical that is a very reactive species in the ice could be involved in a large number of processes implying complex organic molecules (see communication by Pernet et al).
Pauzat, F.; Redondo, P.; Markovits, A.; Ellinger, Y.
Ice Zones: Where We Look for Ice
NSDL National Science Digital Library
In this activity, learners draw conclusions about where on a planetary body scientists might look for ice and why. They use a clay ball, ice cubes, and a heat lamp to model the permanently-shadowed polar regions of planets and moons that may harbor ice. They learn that our Moon, and even Mercury, may have areas with ice. This activity is part of Explore! To the Moon and Beyond! - a resource developed specifically for use in libraries.
Concentrated englacial shear over rigid basal ice, West Antarctica: implications for modelling and ice sheet flow
NASA Astrophysics Data System (ADS)
Basal freeze-on, deformation and ice crystal fabric re-organisation have been invoked to explain thick, massive englacial units observed in the lower ice column of both the Antarctic and Greenland ice sheets. Whilst recognised as having very different rheological properties to overlying meteoric ice, studies assessing the impact of these basal units on the large-scale flow of an ice sheet have so far been limited. We report the discovery of a previously unknown, extensive (100 km long, more than 25 km wide, and up to 1 km thick) englacial unit of near-basal ice beneath the onset zone of the Institute Ice Stream, West Antarctica. Using radio-echo sounding observations, we describe the form and physical characteristics of this englacial unit, and its impact on the stratigraphy and internal deformation of the overlying ice. The lower englacial unit, characterised by a highly-deformed to massive structure, is inferred to be rheologically distinct from the overlying ice column. The overlying ice contains a series of englacial 'whirlwind' features, which are traceable and exhibit longitudinal continuity between flow-orthogonal radar lines. In our data, these whirlwinds are the representation of englacial layer buckling, and therefore provide robust evidence for enhanced ice flow. The interface between the primary ice units is sharp and abrupt, and at a macro-scale is characterised by a series of high-amplitude long-wavelength undulations. Immediately above this interface, whirlwind features are deformed and display evidence for flow-orthogonal horizontal shear, consistent with the deformation of the overlying ice across the basal ice unit. This phenomenon is not a local process, it is observed above the entirety of the currently mapped extent of the basal ice, nor is it dependent on flight orientation, the direction of shear is consistent regardless of flight orientation. These findings have clear significance for our understanding and ability to realistically model ice sheet flow. Our observations suggest that, in parts of the onset zone of the Institute Ice Stream, the flow of the ice sheet effectively ignores the basal topography. Instead, enhanced ice flow responds to a pseudo-bed, with internal deformation concentrated and terminating at an englacial rheological interface between the upper ice sheet column and the massive basal ice. Although we cannot entirely rule out basal accretion as the cause of the strong englacial interface and thick basal layer, discrete englacial shearing acting to realign ice crystals, may be the best explanation for the basal unit in this case. Our results demonstrate that we will, at the very least, need to adapt numerical models of those parts of the ice sheet with extensive and thick basal ice units, and that we may even need to carefully reconsider existing schematic models of ice flow, to incorporate processes associated with concentrated englacial shear.
Ross, Neil; Siegert, Martin
NASA Astrophysics Data System (ADS)
New measurements have been made of the friction coefficient of freshwater polycrystalline ice sliding slowly (5 � 10-8 to 1 � 10-3 m s-1) upon itself at temperatures from 98 to 263 K under low normal stresses (?98 kPa). Sliding obeys Coulomb's law: the shear stress is directly proportional to the normal stress across the interface, while cohesion offers little contribution to frictional resistance. The coefficient of kinetic friction of smooth surfaces varies from ?k = 0.15 to 0.76 and, at elevated temperatures (?223 K), exhibits both velocity strengthening at lower velocities (<10-5 to 10-4 m s-1) and velocity weakening at higher velocities. Strengthening and weakening are attributed to creep deformation of asperities and localized melting, respectively. At intermediate temperatures of 173 and 133 K, the kinetic coefficient appears to not exhibit significant dependence upon velocity. However, at the low temperature of 98 K the coefficient of kinetic friction exhibits moderate velocity strengthening at both the lowest and the highest velocities but velocity independence over the range of intermediate velocities. No effect was detected of either grain size or texture. Over the range of roughness 0.4 � 10-6 m ? Ra ? 12 � 10-6 m, a moderate effect was detected, where ?k ? Ra0.08. Slide-hold-slide experiments revealed that the coefficient of static friction increases by an amount that scales logarithmically with holding time. Implications of the results are discussed in relation to shearing across "tiger stripe" faults within the icy crust of Saturn's Enceladus, sliding of the arctic sea ice cover and brittle compressive failure of cold ice.
Schulson, Erland M.; Fortt, Andrew L.
The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice
NASA Astrophysics Data System (ADS)
This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice-ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the south-western Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that in close proximity to ice shelves this influence should be considered universally when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.
Price, D.; Rack, W.; Langhorne, P. J.; Haas, C.; Leonard, G.; Barnsdale, K.
The sub-ice platelet layer and its influence on freeboard to thickness conversion of Antarctic sea ice
NASA Astrophysics Data System (ADS)
This is an investigation to quantify the influence of the sub-ice platelet layer on satellite measurements of total freeboard and their conversion to thickness of Antarctic sea ice. The sub-ice platelet layer forms as a result of the seaward advection of supercooled ice shelf water from beneath ice shelves. This ice shelf water provides an oceanic heat sink promoting the formation of platelet crystals which accumulate at the sea ice-ocean interface. The build-up of this porous layer increases sea ice freeboard, and if not accounted for, leads to overestimates of sea ice thickness from surface elevation measurements. In order to quantify this buoyant effect, the solid fraction of the sub-ice platelet layer must be estimated. An extensive in situ data set measured in 2011 in McMurdo Sound in the southwestern Ross Sea is used to achieve this. We use drill-hole measurements and the hydrostatic equilibrium assumption to estimate a mean value for the solid fraction of this sub-ice platelet layer of 0.16. This is highly dependent upon the uncertainty in sea ice density. We test this value with independent Global Navigation Satellite System (GNSS) surface elevation data to estimate sea ice thickness. We find that sea ice thickness can be overestimated by up to 19%, with a mean deviation of 12% as a result of the influence of the sub-ice platelet layer. It is concluded that within 100 km of an ice shelf this influence might need to be considered when undertaking sea ice thickness investigations using remote sensing surface elevation measurements.
Price, D.; Rack, W.; Langhorne, P. J.; Haas, C.; Leonard, G.; Barnsdale, K.
Cauchy Relation in Dense H2O Ice VII
By high-pressure Brillouin spectroscopy, sound velocities for all directions and three elastic constants of cubic ice VII have been determined up to 8 GPa at room temperature, with in situ identification of the orientation of the ice VII single crystal grown in a diamond-anvil cell. We have found the unusual result that the Cauchy relation ( C12 = C44) holds
H. Shimizu; M. Ohnishi; S. Sasaki; Y. Ishibashi
A Study of Hexagonal and Cubic Ice at Low Temperatures.
National Technical Information Service (NTIS)
The formation of hexagonal and cubic forms of ice was studied by the use of a cold stage in an electron microscope within the temperature range of -190 to 170 degrees C. Ice crystal specimens were made on cold substrates, i.e., a collodion film, gold foil...
M. Kumai
Electric Charge Transfer Associated with Temperature Gradients in Ice
The development of electric potentials in ice crystals under the influence of temperature gradients is investigated both theoretically and experimentally. The maintenance of a steady temperature gradient across a piece of ice is accompanied by concentration gradients of H^+ and OH^- ions; because of the much greater mobility of H^+ ions, these diffuse more rapidly into the colder part of
J. Latham; B. J. Mason
Proton Spin-Lattice Relaxation in Hexagonal Ice.
National Technical Information Service (NTIS)
The results of measurements of the proton spin-lattice relaxation time T(1) in ice are reported. The ice samples were single crystals grown by zone refining at atmospheric pressure. The measured activation energy for the T(1) process is 14.1 kcal/mole. No...
D. E. Barnaal I. J. Lowe
Ice Nucleation of Re-Dispersed African Desert Dust Samples
NASA Astrophysics Data System (ADS)
Number concentration and size of ice crystals in upper tropospheric cirrus clouds is result of a competition between homogeneous and heterogeneous freezing processes and the dynamic partitioning of water between the interstitial vapour phase and the ice surface. High updraft velocities as e.g. occurring in convective cloud systems favour the formation of high ice particle concentrations by homogeneous freezing of solution aerosols which requires ice supersaturations of up to 60%. At lower updrafts, however, heterogeneous ice nuclei, e.g aircraft emitted soot particles or particles originating from the lower boundary layer, may selectively be activated at lower supersaturation. The pristine ice crystals grow by water uptake, thus eventually limiting the maximum supersaturation to values below the homogeneous freezing threshold. Recent measurements during Crystal-Face have shown mineral dust particles originating from northern Africa to act as efficient ice nuclei in the middle troposphere. Using the large coolable and evacuable aerosol chamber AIDA (Aerosol Interaction and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe, we have investigated the freezing thresholds of redispersed African desert dust samples at different cooling rates and temperatures between -40\\deg{}C and -70\\deg{}C. The mineral dust particles with diameters between about 0.5 and 2 ? m turned out to act as quite effective deposition nuclei at relatively low ice supersaturations. Experimental methods and ice nucleation results will be discussed on the poster. Results from previous AIDA experiments with soot and mineral dust particles coated with sulphuric acid and ammonium sulphate will also be shown.
M�hler, O.; Schnaiter, M.; Wagner, R.; Linke, C.; Saathoff, H.; Schurath, U.; Mangold, A.; Kramer, M.
Physical characteristics of summer sea ice across the Arctic Ocean
Sea ice characteristics were investigated during July and August on the 1994 transect across the Arctic Ocean. Properties examined from ice cores included salinity, temperature, and ice structure. Salinities measured near zero at the surface, increasing to 3-4??? at the ice-water interface. Ice crystal texture was dominated by columnar ice, comprising 90% of the ice sampled. Surface albedos of various ice types, measured with radiometers, showed integrated shortwave albedos of 0.1 to 0.3 for melt ponds, 0.5 for bare, discolored ice, and 0.6 to 0.8 for a deteriorated surface or snow-covered ice. Aerial photography was utilized to document the distribution of open melt ponds, which decreased from 12% coverage of the ice surface in late July at 76??N to almost none in mid-August at 88??N. Most melt ponds were shallow, and depth bore no relationship to size. Sediment was pervasive from the southern Chukchi Sea to the north pole, occurring in bands or patches. It was absent in the Eurasian Arctic, where it had been observed on earlier expeditions. Calculations of reverse trajectories of the sediment-bearing floes suggest that the southernmost sediment was entrained during ice formation in the Beaufort Sea while more northerly samples probably originated in the East Siberian Sea, some as far west as the New Siberian Islands.
Tucker, III, W. B.; Gow, A. J.; Meese, D. A.; Bosworth, H. W.; Reimnitz, E.
NASA Technical Reports Server (NTRS)
This complex area on the side of Europa which faces away from Jupiter shows several types of features which are formed by disruptions of Europa's icy crust. North is to the top of the image, taken by NASA's Galileo spacecraft, and the Sun illuminates the surface from the left. The prominent wide, dark bands are up to 20 kilometers (12 miles) wide and over 50 kilometers (30 miles) long. They are believed to have formed when Europa's icy crust fractured, separated and filled in with darker, 'dirtier' ice or slush from below. A relatively rare type of feature on Europa is the 15-kilometer-diameter (9.3-mile) impact crater in the lower left corner. The small number of impact craters on Europa's surface is an indication of its relatively young age. A region of chaotic terrain south of this impact crater contains crustal plates which have broken apart and rafted into new positions. Some of these 'ice rafts' are nearly 1 kilometer (about half a mile) across. Other regions of chaotic terrain are visible and indicate heating and disruption of Europa's icy crust from below. The youngest features in this scene are the long, narrow cracks in the ice which cut across all other features. One of these cracks is about 30 kilometers (18 miles) to the right of the impact crater and extends for hundreds of miles from the top to the bottom of the image.The image, centered near 23 degrees south latitude and 179 degrees longitude, covers an area about 240 by 215 kilometers (150 by 130 miles) across. The finest details that can be discerned in this picture are about 460 meters (500 yards) across. The image was taken as Galileo flew by Europa on March 29, 1998. The image was taken by the onboard solid state imaging system camera from an altitude of 23,000 kilometers (14,000 miles).The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo
Physiochemical Properties of Sodium Chloride Particles on Laboratory Ice Surfaces
NASA Astrophysics Data System (ADS)
Aqueous halides (e.g. Cl- and Br-) on environmental ice surfaces are converted to reactive gases through heterogeneous chemistry that has broad consequences for springtime Arctic tropospheric oxidation chemistry. Recent studies indicate that atmospherically contaminated snow (e.g. more acidic snow) is more effective at activating halogens than frozen seawater. This study investigates the microstructure created by the addition of salts onto ice surfaces as a function of temperature. Microscopic sodium chloride salt crystals were labeled with a fluorescent dye (fluorescein) and placed onto laboratory ice surface below the hydrohalite (NaCl 2H2O)-water eutectic temperature. As temperature was increased above the eutectic, a discrete brine area formed around the crystal. Size and morphology of the brine area was determined using an Axioscope II epifluorescence microscope. Initially, the salt crystal did not entirely dissolve and three distinct phases (solid salt, brine, ice) were present for some time. Timescales for crystal dissolving, brine formation, and wetting across the ice surfaces where thus constrained. Similar experiments using a fluorescently labeled, laboratory-generated sea salt aerosol particles were also carried out and compared to the larger microscopic sodium chloride crystals. This work gives insight into how atmospheric particles deliver contaminants to ice surfaces, how those contaminants interact with ice surfaces and thus how they may impact halogen activation.
Gleason, E. P.; Simpson, W. R.
Ice Flora (Bottom Type): A Mechanism of Primary Production in Polar Seas and the Growth of Diatoms in Sea Ice.
National Technical Information Service (NTIS)
A field survey off Barrow in the summer of 1964 revealed that sea ice in the Arctic develops a layered structure through the growth of diatoms. The diatoms increase in brine solutions which occur in the microfissures between fine crystals of sea ice and f...
H. Meguro K. Ito H. Fukushima
Color Reveals Translucent Seasonal Ice
NASA Technical Reports Server (NTRS)[figure removed for brevity, see original site] Figure 1 In a region near the south pole of Mars translucent carbon dioxide ice covers the ground seasonally. For the first time we can 'see' the translucent ice by the affect it has on the appearance of the surface below. Dark fans of dust (figure 1) from the surface drape over the top of the seasonal ice. The surface would be the same color as the dust except that the seasonal ice affecting its appearance. Bright bluish streaks are frost that has re-crystallized from the atmosphere. Sunlight can penetrate through the seasonal layer of translucent ice to warm the ground below. That causes the seasonal ice layer to sublime (evaporate) from the bottom rather than the top. Observation Geometry Image PSP_002942_0935 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 13-Mar-2007. The complete image is centered at -86.4 degrees latitude, 99.2 degrees East longitude. The range to the target site was 245.4 km (153.4 miles). At this distance the image scale is 49.1 cm/pixel (with 2 x 2 binning) so objects 147 cm across are resolved. The image shown here has been map-projected to 50 cm/pixel . The image was taken at a local Mars time of 06:41 PM and the scene is illuminated from the west with a solar incidence angle of 82 degrees, thus the sun was about 8 degrees above the horizon. At a solar longitude of 199.6 degrees, the season on Mars is Northern Autumn.
Analysis of Stress Concentration Effects Around Triple Junctions in Lake Vostok Accretion Ice
Due to the thickness of the Antarctic ice cap, the accretion ice just above Lake Vostok Antarctica exists at temperatures close to the melting point. In addition, the large crystals making up this accretion ice are not highly aligned. Therefore, at triple junctions, substantial stress concentrations may exist. This enhanced stress state may subsequently produce additional melting beyond what would
R. L. Brown; E. E. Adams
Retrieval of Surface Solar Radiation Budget under Ice Cloud Sky: Uncertainty Analysis and Parameterization
This study investigates and accounts for the influence of various ice cloud parameters on the retrieval of the surface solar radiation budget (SSRB) from reflected flux at the top of the atmosphere (TOA). The optical properties of ice clouds depend on ice crystal shape, size distribution, water content, and the vertical profiles of geometric and microphysical structure. As a result,
Ying Zhang; Zhanqing Li; Andreas Macke
NSDL National Science Digital Library
This website explores the sentinels of climate change with a 3D interactive global ice viewer. View the effects of climate change on glaciers, sea ice, and continental ice sheets worldwide, in Greenland, Arctic and Antarctica through time lapse movies of ice melt and trends, comparison photographs and maps. Links to NASA satellites and their missions are provided.
Solar heat is the acknowledged driving force for climatic change. However, ice sheets are also capable of causing climatic change. This property of ice sheets derives from the facts that ice and rock are crystalline whereas the oceans and atmosphere are fluids and that ice sheets are massive enough to depress the earth's crust well below sea level. These features
Terence J. Hughes
Examination of Icing Induced Loss of Control and Its Mitigations
NASA Technical Reports Server (NTRS)
Factors external to the aircraft are often a significant causal factor in loss of control (LOC) accidents. In today s aviation world, very few accidents stem from a single cause and typically have a number of causal factors that culminate in a LOC accident. Very often the "trigger" that initiates an accident sequence is an external environment factor. In a recent NASA statistical analysis of LOC accidents, aircraft icing was shown to be the most common external environmental LOC causal factor for scheduled operations. When investigating LOC accident or incidents aircraft icing causal factors can be categorized into groups of 1) in-flight encounter with super-cooled liquid water clouds, 2) take-off with ice contamination, or 3) in-flight encounter with high concentrations of ice crystals. As with other flight hazards, icing induced LOC accidents can be prevented through avoidance, detection, and recovery mitigations. For icing hazards, avoidance can take the form of avoiding flight into icing conditions or avoiding the hazard of icing by making the aircraft tolerant to icing conditions. Icing detection mitigations can take the form of detecting icing conditions or detecting early performance degradation caused by icing. Recovery from icing induced LOC requires flight crew or automated systems capable of accounting for reduced aircraft performance and degraded control authority during the recovery maneuvers. In this report we review the icing induced LOC accident mitigations defined in a recent LOC study and for each mitigation describe a research topic required to enable or strengthen the mitigation. Many of these research topics are already included in ongoing or planned NASA icing research activities or are being addressed by members of the icing research community. These research activities are described and the status of the ongoing or planned research to address the technology needs is discussed
Reehorst, Andrew L.; Addy, Harold E., Jr.; Colantonio, Renato O.
Icing: Accretion, Detection, Protection
NASA Technical Reports Server (NTRS)
The global aircraft industry and its regulatory agencies are currently involved in three major icing efforts: ground icing; advanced technologies for in-flight icing; and tailplane icing. These three major icing topics correspondingly support the three major segments of any aircraft flight profile: takeoff; cruise and hold; and approach and land. This lecture addressess these three topics in the same sequence as they appear in flight, starting with ground deicing, followed by advanced technologies for in-flight ice protection, and ending with tailplane icing.
Reinmann, John J.
NSDL National Science Digital Library
Professor Kenneth Libbrecht at Caltech University is very interested in crystal growth and pattern formation in ice. So interested in fact, he went ahead and created this lovely website (last reviewed in the November 27, 2002 Scout Report) that documents the very wide, and very interesting world, of "snowflakes, snow crystals, and other ice phenomena.�¯�¿�½ First-time visitors should look over the "Snowflake Physics" section, which includes a snowflake primer, crystal faceting, and of course, a set of musings on that much-discussed question: "Is it really true that no two snowflakes are alike?�¯�¿�½ The site also contains a section on "Historic Snowflakes", which contains the thoughts and insights of Johannes Kepler, Rene Descartes and Robert Hooke (among others) on mysteries of snowflakes and snow crystals. The site is rounded out by clutch of snow activities, snowflake "hot spots", and a snowflake image for users" desktops.
Libbrecht, Kenneth G.
Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability
NASA Astrophysics Data System (ADS)
The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosol particles that have re-vitrified in contact with the ice crystals during the preceding homogeneous freezing cycle exhibit pre-activation: they may retain small ice embryos in pores, have footprints on their surface which match the ice lattice, or simply have a much greater surface area or different surface microstructure compared to the unprocessed glassy aerosol particles. Pre-activation must be considered for the correct interpretation of experimental results on the heterogeneous ice nucleation ability of glassy aerosol particles and may provide a mechanism of producing a population of extremely efficient ice nuclei in the upper troposphere.
Wagner, R.; M�hler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.
Ice cloud processing of ultra-viscous/glassy aerosol particles leads to enhanced ice nucleation ability
NASA Astrophysics Data System (ADS)
The ice nucleation potential of airborne glassy aqueous aerosol particles has been investigated by controlled expansion cooling cycles in the AIDA aerosol and cloud chamber of the Karlsruhe Institute of Technology at temperatures between 247 and 216 K. Four different solutes were used as proxies for oxygenated organic matter found in the atmosphere: raffinose, 4-hydroxy-3-methoxy-DL-mandelic acid (HMMA), levoglucosan, and a multi-component mixture of raffinose with five dicarboxylic acids and ammonium sulphate. Similar to previous experiments with citric acid aerosols, all particles were found to nucleate ice heterogeneously before reaching the homogeneous freezing threshold provided that the freezing cycles were started well below the respective glass transition temperatures of the compounds; this is discussed in detail in a separate article. In this contribution, we identify a further mechanism by which glassy aerosols can promote ice nucleation below the homogeneous freezing limit. If the glassy aerosol particles are probed in freezing cycles started only a few degrees below their respective glass transition temperatures, they enter the liquid regime of the state diagram upon increasing relative humidity (moisture-induced glass-to-liquid transition) before being able to act as heterogeneous ice nuclei. Ice formation then only occurs by homogeneous freezing at elevated supersaturation levels. When ice forms the remaining solution freeze concentrates and re-vitrifies. If these ice cloud processed glassy aerosol particles are then probed in a second freezing cycle at the same temperature, they catalyse ice formation at a supersaturation threshold between 5 and 30% with respect to ice. By analogy with the enhanced ice nucleation ability of insoluble ice nuclei like mineral dusts after they nucleate ice once, we refer to this phenomenon as pre-activation. We propose a number of possible explanations for why glassy aerosols that have re-vitrified in contact with the ice crystals during the preceding homogeneous freezing cycle exhibit pre-activation: they may retain small ice embryos in pores, have footprints on their surface which match the ice lattice, or simply have a much greater surface area or different surface microstructure compared to the unprocessed glassy aerosol particles. Pre-activation must be considered for the correct interpretation of experimental results on the heterogeneous ice nucleation ability of glassy aerosol particles and may provide a mechanism of producing a population of extremely efficient ice nuclei in the upper troposphere.
Wagner, R.; M�hler, O.; Saathoff, H.; Schnaiter, M.; Skrotzki, J.; Leisner, T.; Wilson, T. W.; Malkin, T. L.; Murray, B. J.
NASA Astrophysics Data System (ADS)
The location and behaviour of ice streams is one of the most important controls on ice sheet configuration and stability. In order to reconstruct former ice sheets we need to know ice stream location and timing. Once identified, the beds of palaeo-ice streams provide an unprecedented opportunity to glean information about their basal environment, something that remains very difficult under contemporary ice streams. This paper represents the first synthesis and discussion of palaeo-ice stream research from a variety of former ice sheets and includes new insights relating their configuration and activity to the evidence they leave behind. The ambiguous use of the term 'ice stream' is addressed and four possible configurations for ice streams are presented. Diagnostic landforms and landform assemblages that we would expect an ice stream to produce are discussed and the temporal context of bedform generation is described as either a 'rubber stamped' or 'smudged' bedform imprint, resulting from isochronous or time-transgressive landform generation. In particular, we focus on the configuration of terrestrially terminating ice streams, for which there are no modern analogues. Technological advances in marine geophysics are helping to generate a convergence of interest between Antarctic glaciology and palaeo glaciology. It is suggested that investigations around the fringes of contemporary ice sheets, (i.e. West Antarctica) can provide evidence that directly links the geomorphological record of palaeo-ice streams with their contemporary counterparts. In addition, computational advances and modelling adaptations have permitted the incorporation of ice streams within ice sheet models. We argue that data from palaeo-ice stream beds are invaluable to ice sheet/stream modelling experiments and will help us understand ice stream operation and the linkages between climate perturbations and both palaeo and contemporary ice sheets.
Stokes, Chris R.; Clark, Chris D.
Fast flowing ice streams and outlet glaciers provide the major avenues for ice flow from past and present ice sheets. These ice streams move faster than the surrounding ice sheet by a factor of one hundred or more. Several mechanisms for fast ice stream flow have been identified, leading to a spectrum of different ice stream types. In this paper
Martin Truffer; Keith A. Echelmeyer
Black carbon enrichment in atmospheric ice particle residuals observed in lower tropospheric mixed phase clouds
The enrichment of black carbon (BC) in residuals of small ice crystals was investigated during intensive experiments in winter 2004 and 2005 at the high alpine research station Jungfraujoch (3580 m asl, Switzerland). Two inlets were used to sample the bulk aerosol (residuals of cloud droplets and ice crystals as well as non-activated aerosol particles) and the residual particles of small ice crystals (diameter 5 - 20 ?m). An enrichment of the BC mass fraction in the ice particle residuals was observed by investigating the measured BC mass concentration as a fraction of the bulk (submicrometer) aerosol mass concentration sampled by the two inlets. On average, the BC mass fraction was 5% for the bulk aerosol and 27% for the ice particle residuals. The observed enrichment of BC in ice particle residuals suggests that BC containing particles preferentially act as ice nuclei, with important implications for the indirect aerosol effect via glaciation of clouds.
Cozic, J.; Mertes, S.; Verheggen, B.; Cziczo, Daniel J.; Gallavardin, S. J.; Walter, S.; Baltensperger, Urs; Weingartner, E.
Analytical Tools for Cloudscope Ice Measurement.
National Technical Information Service (NTIS)
The cloudscope is a ground or aircraft instrument for viewing ice crystals impacted on a sapphire window. It is essentially a simple optical microscope with an attached compact CCD video camera whose output is recorded on a Hi-8 mm video cassette recorder...
W. P. Arnott
A Laboratory Route to Interstellar Ice
NASA Astrophysics Data System (ADS)
The formation of snow and ice has always intrigued humans and challenged them to study these phenomena. Every snowflake has its own unique history of formation, but no two are alike. Like snow-crystals, interstellar ices consist predominantly of water (H2O), but also contain significant fractions of other molecules such as carbon monoxide (CO), carbon dioxide (CO2), and methanol (CH3OH), and traces of dinitrogen (N2) and ammonia (NH3). The presence, or absence, of a molecule in the ice strongly depends on the environmental conditions. Vice versa, these molecules have an influence on their environment as well. Hence, the chemical composition and the structure of interstellar ices are thought to contain valuable information about the past and the future of interstellar regions, and it is for this reason that interstellar ices are simulated and studied under laboratory conditions. The present thesis contains a study of laboratory analogs of interstellar ices and presents a newly developed apparatus that provides a novel laboratory route to investigate the properties of these ices in more detail than has previously been possible.
van Broekhuizen, Fleur Antoinette
The development of offshore oil and gas resources in the Arctic waters of Alaska requires offshore structures which successfully resist the lateral forces due to moving, drifting ice. Ice islands are floating, a tabular icebergs, up to 60 meters thick, of solid ice throughout their thickness. The ice islands are thus regarded as the strongest ice features in the Arctic; fixed offshore structures which can directly withstand the impact of ice islands are possible but in some locations may be so expensive as to make oilfield development uneconomic. The resolution of the ice island problem requires two research steps: (1) calculation of the probability of interaction between an ice island and an offshore structure in a given region; and (2) if the probability if sufficiently large, then the study of possible interactions between ice island and structure, to discover mitigative measures to deal with the moving ice island. The ice island research conducted during the 1983-1988 interval, which is summarized in this report, was concerned with the first step. Monte Carlo simulations of ice island generation and movement suggest that ice island lifetimes range from 0 to 70 years, and that 85% of the lifetimes are less then 35 years. The simulation shows a mean value of 18 ice islands present at any time in the Arctic Ocean, with a 90% probability of less than 30 ice islands. At this time, approximately 34 ice islands are known, from observations, to exist in the Arctic Ocean, not including the 10-meter thick class of ice islands. Return interval plots from the simulation show that coastal zones of the Beaufort and Chukchi Seas, already leased for oil development, have ice island recurrences of 10 to 100 years. This implies that the ice island hazard must be considered thoroughly, and appropriate safety measures adopted, when offshore oil production plans are formulated for the Alaskan Arctic offshore. 132 refs., 161 figs., 17 tabs.
Sackinger, W.M.; Jeffries, M.O.; Lu, M.C.; Li, F.C.
Polarimetric Signatures of Sea Ice. Part 1; Theoretical Model
NASA Technical Reports Server (NTRS)
Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.
Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.
Polarimetric signatures of sea ice. 1: Theoretical model
NASA Technical Reports Server (NTRS)
Physical, structral, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarmetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies to interpretation of sea ice polarimetric signatures.
Nghiem, S. V.; Kwok, R.; Yueh, S. H.; Drinkwater, M. R.
NSDL National Science Digital Library
This website, from Caltech, contains the basic facts about snowflakes and snow crystals, along with many images. The structure of ice, the basic form of a snowflake, the dependence of shape on temperature and humidity, and growing "designer snowflakes" in the lab are described. Links provide more information and image galleries.
Libbrecht, Kenneth
NASA Astrophysics Data System (ADS)
Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters.
Arrigo, Kevin R.
Polar sea ice is one of the largest ecosystems on Earth. The liquid brine fraction of the ice matrix is home to a diverse array of organisms, ranging from tiny archaea to larger fish and invertebrates. These organisms can tolerate high brine salinity and low temperature but do best when conditions are milder. Thriving ice algal communities, generally dominated by diatoms, live at the ice/water interface and in recently flooded surface and interior layers, especially during spring, when temperatures begin to rise. Although protists dominate the sea ice biomass, heterotrophic bacteria are also abundant. The sea ice ecosystem provides food for a host of animals, with crustaceans being the most conspicuous. Uneaten organic matter from the ice sinks through the water column and feeds benthic ecosystems. As sea ice extent declines, ice algae likely contribute a shrinking fraction of the total amount of organic matter produced in polar waters. PMID:24015900
Arrigo, Kevin R
Some formation peculiarities of physical and mechanical ice characteristics in hummocky formations
Main differences are considered in the formation of physical and mechanical ice properties in hummocky formations as compared\\u000a with level areas of the ice cover. The results of laboratory and field investigations demonstrate that these differences are\\u000a caused both by dynamometamorphic transformations of crystal ice structure as a result of the compression of ice fields before\\u000a the beginning of hummocky
K. P. Tyshko
Intercellular ice propagation: experimental evidence for ice growth through membrane pores.
Propagation of intracellular ice between cells significantly increases the prevalence of intracellular ice in confluent monolayers and tissues. It has been proposed that gap junctions facilitate ice propagation between cells. This study develops an equation for capillary freezing-point depression to determine the effect of temperature on the equilibrium radius of an ice crystal sufficiently small to grow through gap junctions. Convection cryomicroscopy and video image analysis were used to examine the incidence and pattern of intracellular ice formation (IIF) in the confluent monolayers of cell lines that do (MDCK) and do not (V-79W) form gap junctions. The effect of gap junctions on intracellular ice propagation was strongly temperature-dependent. For cells with gap junctions, IIF occurred in a directed wave-like pattern in 100% of the cells below -3 degrees C. At temperatures above -3 degrees C, there was a marked drop in the incidence of IIF, with isolated individual cells initially freezing randomly throughout the sample. This random pattern of IIF was also observed in the V-79W monolayers and in MDCK monolayers treated to prevent gap junction formation. The significant change in the low temperature behavior of confluent MDCK monolayers at -3 degrees C is likely the result of the inhibition of gap junction-facilitated ice propagation, and supports the theory that gap junctions facilitate ice nucleation between cells.
Acker, J P; Elliott, J A; McGann, L E
Physical and biological controls on DMS,P dynamics in ice shelf-influenced fast ice during a winter-spring and a spring-summer transitions
NASA Astrophysics Data System (ADS)
report the seasonal and vertical variations of dimethylsulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) in fast ice at Cape Evans, McMurdo Sound (Antarctica) during the spring-summer transition in 2011 and winter-spring transition in 2012. We compare the variations of DMS,P observed to the seasonal evolution of the ice algal biomass and of the physical properties of the ice cover, with emphasis on the ice texture and brine dynamics. Isolated DMS and DMSP maxima were found during both seasonal episodes in interior ice and corresponded to the occurrence of platelet crystals in the ice texture. We show that platelet crystals formation corresponded in time and depth to the incorporation of dinoflagellates (strong DMSP producers) in the ice cover. We also show that platelet crystals could modify the environmental stresses on algal cells and perturb the vertical redistribution of DMS,P concentrations. We show that during the winter-spring transition in 2012, the DMS,P profiles were strongly influenced by the development and decline of a diatom-dominated bloom in the bottom ice, with DMSP variations remarkably following chl a variations. During the spring-summer transition in 2011, the increase in brine volume fraction (influencing ice permeability) on warming was shown to trigger (1) an important release of DMS to the under-ice water through brine convection and (2) a vertical redistribution of DMSP across the ice.
Carnat, Gauthier; Zhou, Jiayun; Papakyriakou, Tim; Delille, Bruno; Goossens, Thomas; Haskell, Tim; Schoemann, V�ronique; Fripiat, Fran�ois; Rintala, Janne-Markus; Tison, Jean-Louis
Digital-image processing and image analysis of glacier ice
This document provides a methodology for extracting grain statistics from 8-bit color and grayscale images of thin sections of glacier ice�a subset of physical properties measurements typically performed on ice cores. This type of analysis is most commonly used to characterize the evolution of ice-crystal size, shape, and intercrystalline spatial relations within a large body of ice sampled by deep ice-coring projects from which paleoclimate records will be developed. However, such information is equally useful for investigating the stress state and physical responses of ice to stresses within a glacier. The methods of analysis presented here go hand-in-hand with the analysis of ice fabrics (aggregate crystal orientations) and, when combined with fabric analysis, provide a powerful method for investigating the dynamic recrystallization and deformation behaviors of bodies of ice in motion. The procedures described in this document compose a step-by-step handbook for a specific image acquisition and data reduction system built in support of U.S. Geological Survey ice analysis projects, but the general methodology can be used with any combination of image processing and analysis software. The specific approaches in this document use the FoveaPro 4 plug-in toolset to Adobe Photoshop CS5 Extended but it can be carried out equally well, though somewhat less conveniently, with software such as the image processing toolbox in MATLAB, Image-Pro Plus, or ImageJ.
Fitzpatrick, Joan J.
Ice nucleation studies of meteoric smoke analogues
NASA Astrophysics Data System (ADS)
Nano-sized meteoric smoke particles, formed subsequently to the ablation of meteors in the Earth's upper atmosphere, are currently the favoured candidate for the heterogeneous nucleation of ice clouds (noctilucent / polar mesospheric) in the mesosphere. However, many fundamental aspects of these aerosol species such as composition, shape and nucleation efficiency remain effectively unknown. Following our earlier work on the generation and characterisation of likely smoke particle analogues including amorphous iron oxides and silicates of non-spherical, low density nature, we are currently investigating the heterogeneous ice nucleating capacity of such nanomaterials. There is currently nothing in the literature in this regard for such refractory aerosol species under conditions relevant to the upper atmosphere and at nanoparticle dimensions (< 100 nm), expected to be present at such high altitudes. It is to this end that we have conducted a series of low temperature nucleation studies on samples of such analogue species at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) chamber in Karlsruhe, Germany. This facility affords the study of the deposition mode ice nucleation of aerosol particles injected into the chamber volume at temperatures down to 183 K and pressures less than 1 Pa. In-situ monitoring of particle size distribution, ice crystal growth and light scattering along with ambient conditions of pressure, temperature and supersaturation levels with respect to both water and ice in the chamber were carried out. We report on the critical threshold conditions of temperature and ice supersatuation under which heterogeneous ice nucleation is activated by the particle samples in an effort to establish the relative activation efficiencies of such materials as ice nuclei and their proposed participation in the formation of mesospheric ice clouds.
Saunders, Russell; Moehler, Ottmar; Schnaiter, Martin; Benz, Stefan; Plane, John M. C.
Ice Tank Experiments on the Thermodynamics of Deformed Ice.
National Technical Information Service (NTIS)
Deformed ice features such as ridged ice, rafted ice, and brash ice present obstacles to ship navigation. The resistance to ship motion depends in part on the degree to which the deformed ice and water near the water surface consolidate. A series of ice t...
B. Veitch P. Kujala P. Keiley E. Lehmus
Assessing aerosol indirect effect through ice clouds in CAM5
NASA Astrophysics Data System (ADS)
Ice clouds play an important role in regulating the Earth's radiative budget and influencing the hydrological cycle. Aerosols can act as solution droplets or ice nuclei for ice crystal formation, thus affecting the physical properties of ice clouds. Because the related dynamical and microphysical processes happen at very small spatial and temporal scales, it is a great challenge to accurately represent them in global climate models. Consequently, the aerosol indirect effect through ice clouds (ice AIE) estimated by global climate models is associated with large uncertainties. In order to better understand these processes and improve ice cloud parameterization in the Community Atmospheric Model, version 5 (CAM5), we analyze in-situ measurements from various research campaigns, and use the derived statistical information to evaluate and constrain the model [1]. We also make use of new model capabilities (prescribed aerosols and nudging) to estimate the aerosol indirect effect through ice clouds, and quantify the uncertainties associated with ice nucleation processes. In this study, a new approach is applied to separate the impact of aerosols on warm and cold clouds by using the prescribed-aerosol capability in CAM5 [2]. This capability allows a single simulation to simultaneously include up to three aerosol fields: online calculated, as well as prescribed pre-industrial (PI) and present-day conditions (PD). In a set of sensitivity simulations, we use the same aerosol fields to drive droplet activation in warm clouds, and different (PD and PI) conditions for different components of the ice nucleation parameterization in pure ice clouds, so as to investigate various ice nucleation mechanisms in an isolated manner. We also applied nudging in our simulations, which helps to increase the signal-to-noise ratio in much shorter simulation period [3] and isolate the impact of aerosols on ice clouds from other factors, such as temperature and relative humidity change. The results show that homogeneous ice nucleation is the main contributor that leads to strong longwave ice AIE in this model. The estimated PD-PI longwave cloud forcing (LWCF) change is strongly sensitive to the simulated sub-grid updraft velocity. Considering the effect of pre-existing ice crystals on ice nucleation can help to significantly reduce the LWCF change. In comparison, the effect of heterogeneous ice nuclei spectra is relatively small, although the perturbations in the LWCF and shortwave cloud forcing are still non-negligible.
Zhang, Kai; Liu, Xiaohong; Yoon, Jin-Ho; Wang, Minghuai; Comstock, Jennifer M.; Barahona, Donifan; Kooperman, Gabriel
Ice-binding mechanism of winter flounder antifreeze proteins.
We have studied the winter flounder antifreeze protein (AFP) and two of its mutants using molecular dynamics simulation techniques. The simulations were performed under four conditions: in the gas phase, solvated by water, adsorbed on the ice (2021) crystal plane in the gas phase and in aqueous solution. This study provided details of the ice-binding pattern of the winter flounder AFP. Simulation results indicated that the Asp, Asn, and Thr residues in the AFP are important in ice binding and that Asn and Thr as a group bind cooperatively to the ice surface. These ice-binding residues can be collected into four distinct ice-binding regions: Asp-1/Thr-2/Asp-5, Thr-13/Asn-16, Thr-24/Asn-27, and Thr-35/Arg-37. These four regions are 11 residues apart and the repeat distance between them matches the ice lattice constant along the (1102) direction. This match is crucial to ensure that all four groups can interact with the ice surface simultaneously, thereby, enhancing ice binding. These Asx (x = p or n)/Thr regions each form 5-6 hydrogen bonds with the ice surface: Asn forms about three hydrogen bonds with ice molecules located in the step region while Thr forms one to two hydrogen bonds with the ice molecules in the ridge of the (2021) crystal plane. Both the distance between Thr and Asn and the ordering of the two residues are crucial for effective ice binding. The proper sequence is necessary to generate a binding surface that is compatible with the ice surface topology, thus providing a perfect "host/guest" interaction that simultaneously satisfies both hydrogen bonding and van der Waals interactions. The results also show the relation among binding energy, the number of hydrogen bonds, and the activity. The activity is correlated to the binding energy, and in the case of the mutants we have studied the number of hydrogen bonds. The greater the number of the hydrogen bonds the greater the antifreeze activity. The roles van der Waals interactions and the hydrophobic effect play in ice binding are also highlighted. For the latter it is demonstrated that the surface of ice has a clathratelike structure which favors the partitioning of hydrophobic groups to the surface of ice. It is suggested that mutations that involve the deletion of hydrophobic residues (e.g., the Leu residues) will provide insight into the role the hydrophobic effect plays in partitioning these peptides to the surface of ice. Images FIGURE 4 FIGURE 5 FIGURE 6 FIGURE 7 FIGURE 8 FIGURE 11
Cheng, A; Merz, K M
NSDL National Science Digital Library
This website presents the results of the analysis of Great Lakes ice charts dating back to 1960. After learning about the methods used to produce this online atlas, users can view the original ice charts. Researchers can find data on first ice, last ice, ice duration, and other ice related statistics. Students and educators can learn about variations in ice cover through the animations of ice cover time series. The website offers downloads of a few of the references and technical issues.
Quantifying and Reducing Biases in Satellite Derived Ice Cloud Optical Thickness and Ice Effective Diameter by Simultaneous Retrievals of Ice Asymmetry Parameter
NASA Astrophysics Data System (ADS)
The ice cloud optical thickness (COT) and the ice crystal effective diameter (Deff), defined as one-and-one-half times the bulk ice volume over the bulk ice projected area, are fundamental radiative properties of ice clouds and provide valuable constraints for cloud model simulations. These parameters can be retrieved from satellite, in situ or ground-based measurements, although COT and Deff derived from such sensors are known to differ significantly amongst each other and biases need to be better quantified. Here we focus on COT and Deff at cloud top derived from satellite measurements in the visible and shortwave infrared. For such retrievals, the leading source of uncertainty is related to the asymmetry parameter of the ice optical model assumed in the retrieval algorithm. We first quantify the biases in retrieved COT and Deff as a function of bias in assumed asymmetry parameter. We then present a method to retrieve ice cloud asymmetry parameter from multi-directional polarization measurements, which allows for subsequent retrievals of COT and Deff that are not biased by a preselected ice optical model. This method is applied to combined measurements of the POLDER and MODIS satellite instruments over deep convection observed during the TWP-ICE campaign. We show that retrieved ice crystal asymmetry parameter and Deff vary systematically with cloud-top temperature, but even more so with changes of monsoon activity. Using both TWP-ICE and global measurements, we show that our retrieved COT values are significantly smaller than current operational MODIS collection 5 retrievals, because our retrieved asymmetry parameters are systematically smaller than those assumed in the operational retrievals. Moreover, the retrieved Deff values are generally 20-50% larger than operational MODIS retrievals and show a significantly wider range. Based on these results, we note expected improvements and limitations of upcoming MODIS collection 6 retrievals. Finally, we briefly discuss the use of our retrievals for evaluating cloud-resolving model simulations.
van Diedenhoven, B.; Fridlind, A. M.; Ackerman, A. S.; Cairns, B.
Observation of Sea Ice Surface Thermal States Under Cloud Cover
NASA Technical Reports Server (NTRS)
Clouds interfere with the distribution of short-wave and long-wave radiations over sea ice, and thereby strongly affect the surface energy balance in polar regions. To evaluate the overall effects of clouds on climatic feedback processes in the atmosphere-ice-ocean system, the challenge is to observe sea ice surface thermal states under both clear sky and cloudy conditions. From laboratory experiments, we show that C-band radar (transparent to clouds) backscatter is very sensitive to the surface temperature of first-year sea ice. The effect of sea ice surface temperature on the magnitude of backscatter change depends on the thermal regimes of sea ice thermodynamic states. For the temperature range above the mirabilite (Na2SO4.10H20) crystallization point (-8.2 C), C-band data show sea ice backscatter changes by 8-10 dB for incident angles from 20 to 35 deg at both horizontal and vertical polarizations. For temperatures below the mirabilite point but above the crystallization point of MgCl2.8H2O (-18.0 C), relatively strong backwater changes between 4-6 dB are observed. These backscatter changes correspond to approximately 8 C change in temperature for both cases. The backscattering mechanism is related to the temperature which determines the thermodynamic distribution of brine volume in the sea ice surface layer. The backscatter is positively correlated to temperature and the process is reversible with thermodynamic variations such as diurnal insolation effects. From two different dates in May 1993 with clear and overcast conditions determined by the Advanced Very High Resolution Radiometer (AVHRR), concurrent Earth Resources Satellite 1 (ERS-1) C-band ice observed with increases in backscatter over first-year sea ice, and verified by increases in in-situ sea ice surface temperatures measured at the Collaborative-Interdisciplinary Cryosphere Experiment (C-ICE) site.
Nghiem, S. V.; Perovich, D. K.; Gow, A. J.; Kwok, R.; Barber, D. G.; Comiso, J. C.; Zukor, Dorothy J. (Technical Monitor)
Thermal Ice Pressure in Lake Ice Covers.
National Technical Information Service (NTIS)
The temperature changes of land-fast ice covers will give rise to loads against shores and hydraulic structures. The magnitude and frequency of such thermal ice pressures are important with respect to the design of hydraulic structures. A numerical model ...
L. Bergdahl
Assessment of ice particle growth processes at dye-3, Greenland
NASA Astrophysics Data System (ADS)
As part of the DGASP program on the Greenland Ice Sheet, an investigation was conducted into the nature of ice particle formation processes that result in the formation of snow. Ice particle habits were determined using Formvar replicas of falling snow crystals. From these measurements an assessment of the primary growth process and altitude of formation was made. Results indicate that the scavenging of cloud water by falling ice particles, growth by accretion or riming, rarely occurs. However, when riming does occur, it is usually associated with warmer air masses from the south. The occurrence of riming was also observed to be dependent on the season, with a greater frequency occurring during warmer months. It was estimated that ice particle riming contributes less than 5% of the average annual water mass, but up to 30% of the deposition of some chemical species, deposited to the Greenland Ice Sheet at Dye 3. Ice particle habits indicate that they originate at higher altitudes above the ice cap in summer than in winter. Variations in the magnitude of ice particle riming, the elevation of origin of ice particles, the meteorology and the season of the year are all essential when interpreting snow chemistry and comparing snow and aerosol chemistry at Dye 3.
Borys, Randolph D.; Del Vecchio, Deborah; Jaffrezo, Jean-Luc; Davidson, Cliff I.; Mitchell, David L.
Ice depolarization on low-angle 2 GHz satellite downlinks
NASA Technical Reports Server (NTRS)
The impact of ice depolarization on the statistical performance of satellite downlinks were investigated. Propagation data recorded during 1979 and 1980 to see what impact of ice depolarization on link performance were analyzed. The effects on the cross polarization discrimination (XPD) statistics amounted to at most a 2 to 4 dB reduction in the XPD values which rain would have produced for a given percentage of time. Ice depolarization had no effect on the statistics of XPD values below the 0.01% level. Most of the severe ice depolarization events were associated with drops in barometric pressure and the passage of intense cold fronts through our area. Ice contents as the product of three individually undetermined quantities were defined: ice particle density, ice cloud thickness, and the average volume of the ice crystals. It is indicated that populations of ice particle with ice contents on the order of 0.002 m4/m3 are probably responsible for the lower values of measured XPD.
Stutzman, W. L.; Bostian, C. W.; Tsolakis, A.; Pratt, T.
Inuit hunters of the North have long recognized ice as the natural state of water from which life flows on Earth. Although unaware of the microscopic world, they chart changes in properties of ice and water that derive from a succession of microbial inhabitants. Scientific hunters of the West have largely overlooked all but the warmest of ices as dynamic
Jody Deming
National Technical Information Service (NTIS)
A series of 33 charts is presented to illustrate the ice cover on the Great Lakes for three classifications of winter; mild, normal and severe. Six ice charts are provided for each of the Great Lakes. Two charts show the maximum extent of ice cover during...
D. R. Rondy
NSDL National Science Digital Library
This information about the Lunar Prospector mission to the Moon discusses the possibility that ice exists on the lunar surface. The article indicates that no native water ice has been found on the moon. If ice has been found, it most likely originated from meteors and meteorites which periodically bombard the lunar surface.
Williams, David
ERIC Educational Resources Information Center
Describes experiments in ice physics that demonstrate the behavior and properties of ice. Show that ice behaves as an ionic conductor in which charge is transferred by the movement of protons, its electrical conductivity is highly temperature-dependent, and its dielectric properties show dramatic variation in the kilohertz range. (Author/GA)
Martin, P. F.; And Others
NSDL National Science Digital Library
This lesson will pique your students' interest by reading about Curious George and his ice cream adventure. Students will move from George's adventure to a class chart of favorite ice cream flavors to organizing and completing their own ice cream chart.
Worley, Chris
The opacity of ice formed from water containing dissolved air is due to the presence of bubbles of air in the ice. Both bubble concentration and sizes were found to depend on the rate of freezing. Bulk water saturated with air at 0�C was found to freeze into ice containing about six bubbles per mm3 when freezing proceeded at 0.5
A E Carte
Ice composition evidence of marine ice transfer along the bottom of small Antarctic ice shelf
The existence of marine ice transfer along the underside of the Hell's Gate Ice Shelf (Victoria Land), is indicated by an isotopic and chemical study of ice cores. Because of top surface ablation, the marine ice formed at the ice shelf-ocean interface, ultimately appears at shelf surface. A succession of congelation, platelet and frazil ice is shown to occur. The
R. Souchez; M. Meneghel; J.-L. Tison; R. Lorrain; D. Ronveaux; C. Baroni; A. Lozej; I. Tabacco; J. Jouzel
In situ observations of a high-pressure phase of H2O ice
A previously unknown solid phase of H2O has been identified by its peculiar growth patterns, distinct pressure-temperature melting relations, and vibrational Raman spectra. Morphologies of ice crystals and their pressure-temperature melting relations were directly observed in a hydrothermal diamond-anvil cell for H2O bulk densities between 1203 and 1257 kilograms per cubic meter at temperatures between -10??and 50??C. Under these conditions, four different ice forms were observed to melt: two stable phases, ice V and ice VI, and two metastable phases, ice IV and the new ice phase. The Raman spectra and crystal morphology are consistent with a disordered anisotropic structure with some similarities to ice VI.
Chou, I. -M.; Blank, J. G.; Goncharov, A. F.; Mao, H. -K.; Hemley, R. J.
Black carbon enrichment in atmospheric ice particle residuals observed in lower trophospheric mixed phase clouds
The enrichment of black carbon (BC) in residuals of small ice particles was investigated during intensive experiments in winter 2004 and 2005 at the high alpine research station Jungfraujoch (3580 m asl, Switzerland). Two inlets were used to sample the bulk aerosol (residuals of cloud droplets and ice crystals as well as non-activated aerosol particles) and the residual particles of small ice crystals (diameter 5 - 20 m). An enrichment of the BC mass fraction in the ice particle residuals was observed by investigating the measured BC mass concentration as a fraction of the bulk (submicrometer) aerosol mass concentration sampled by the two inlets. On average, the BC mass fraction was 5% for the bulk aerosol and 14% for the ice particle residuals. The observed enrichment of BC in ice particle residuals suggests that BC may act as ice nuclei, with important implications for the indirect aerosol effect via glaciation of clouds.
Cozic, J.; Mertes, S.; Verheggen, B.; Cziczo, Dan; Gallavardin, S. J.; Walter, S.; Baltensperger, Urs; Weingartner, E.
Ice-templated structures for biomedical tissue repair: From physics to final scaffolds
NASA Astrophysics Data System (ADS)
Ice-templating techniques, including freeze-drying and freeze casting, are extremely versatile and can be used with a variety of materials systems. The process relies on the freezing of a water based solution. During freezing, ice nucleates within the solution and concentrates the solute in the regions between the growing crystals. Once the ice is removed via sublimation, the solute remains in a porous structure, which is a negative of the ice. As the final structure of the ice relies on the freezing of the solution, the variables which influence ice nucleation and growth alter the structure of ice-templated scaffolds. Nucleation, the initial step of freezing, can be altered by the type and concentration of solutes within the solution, as well as the set cooling rate before freezing. After nucleation, crystal growth and annealing processes, such as Ostwald ripening, determine the features of the final scaffold. Both crystal growth and annealing are sensitive to many factors including the set freezing temperature and solutes. The porous structures created using ice-templating allow scaffolds to be used for many diverse applications, from microfluidics to biomedical tissue engineering. Within the field of tissue engineering, scaffold structure can influence cellular behavior, and is thus critical for determining the biological stimulus supplied by the scaffold. The research focusing on controlling the ice-templated structure serves as a model for how other ice-templating systems might be tailored, to expand the applications of ice-templated structures to their full potential.
Pawelec, K. M.; Husmann, A.; Best, S. M.; Cameron, R. E.
A comprehensive Atlas of Alaska marine ice is presented. It includes information on pack and landfast sea ice and calving tidewater glacier ice. It also gives information on ice and related environmental conditions collected over several years time and indicates the normal and extreme conditions that might be expected in Alaska coastal waters. Much of the information on ice conditions in Alaska coastal waters has emanated from research activities in outer continental shelf regions under assessment for oil and gas exploration and development potential. (DMC)
LaBelle, J.C.; Wise, J.L.; Voelker, R.P.; Schulze, R.H.; Wohl, G.M.
NASA Astrophysics Data System (ADS)
To support its program of studying ice cores taken from the Greenland, Antarctic and midlatitude ice sheets, the Division of Polar Programs of the National Science Foundation is soliciting proposals for operating its ice core curatorial facility.NSF's current ice core repository is at the State University of New York at Buffalo, where it has been operated under annual contract since 1975. Beginning in Fiscal Year 1991, whoever manages the NSF facility, now to be called the U.S. Ice Core Repository, will do it under a 5-year cooperative agreement.
Physical processes controlling ice concentrations in synoptically forced, midlatitude cirrus
NASA Astrophysics Data System (ADS)
Numerical simulations and airborne measurements are used to evaluate the impact of physical processes on synoptically forced, midlatitude cirrus ice concentrations. The agreement within a factor of 2 between ice concentrations measured with independent techniques (replicators and optical imaging probes) provides confidence in the accuracy of the in situ measurements. We use a computationally efficient modeling approach that incorporates the key cirrus physical processes, such that thousands of cloud cases can be simulated and the model results can be statistically compared with observations. One-dimensional simulations with detailed treatments of cloud microphysical processes are driven by temperatures and vertical winds extracted from meteorological analyses. Small-scale temperature and vertical wind perturbations associated with mesoscale waves are superimposed on the analysis fields. We find that in simulations with only homogeneous freezing nucleation, ice concentration statistics are very sensitive to the specified mesoscale wave vertical wind perturbations. With the frequency distribution of vertical winds adjusted to agree with aircraft observations, we obtain good agreement between the simulated and observed ice concentration frequency distributions. Both the observations and simulations indicate that relatively high ice concentrations (?1000 L-1) occur rarely in these clouds (less than 1% of the time). Simulations including both homogeneous and heterogeneous nucleation indicate that even with moderate concentrations of ice nuclei (20 L-1), heterogeneous nucleation is an important ice production process, particularly for relatively low ice concentrations and warm temperatures. With enhanced ice nuclei concentrations (100 L-1), heterogeneous nucleation dominates ice production in the model. We find that it is critically important to include the impact of sedimentation on the evolution of ice concentrations when comparing model results with observations. Ice crystal collection efficiencies are poorly constrained at low temperatures, and we find that aggregation can significantly reduce ice concentrations. Sensitivity tests indicate that neither the agreement between observed and simulated ice crystal statistics nor the sensitivities indicated by the simulations are significantly affected by model assumptions such as the time periods simulated, geographic domain covered, trajectory paths calculated, or ice crystal habit assumed.
Jensen, E. J.; Lawson, R. P.; Bergman, J. W.; Pfister, L.; Bui, T. P.; Schmitt, C. G.
Validation of the use of heat transfer models in liquid\\/solid fluidized beds for ice slurry generation
Heat transfer coefficients in a liquid\\/solid fluidized bed heat exchanger are investigated for application in ice slurry generators. A range of temperature driving forces is determined in which ice slurry generation is stable. In this range ice crystal formation or growth does not affect heat transfer coefficients. A model is proposed that accurately predicts heat transfer coefficients in the fluidized
J. W. Meewisse; C. A. Infante Ferreira
The role of secondary refrigerants is expected to grow as the focus on the reduction of greenhouse gas emissions increases. The effectiveness of secondary refrigerants can be improved when phase changing media are introduced in place of single phase media. Operating at temperatures below the freezing point of water, ice slurry facilitates several efficiency improvements such as reductions in pumping energy consumption as well as lowering the required temperature difference in heat exchangers due to the beneficial thermo-physical properties of ice slurry. Research has shown that ice slurry can be engineered to have ideal ice particle characteristics so that it can be easily stored in tanks without agglomeration and then be extractable for pumping at very high ice fraction without plugging. In addition ice slurry can be used in many direct contact food and medical protective cooling applications. This paper provides an overview of the latest developments in ice slurry technology.
Kauffeld, M.; WANG, M. J.; Goldstein, V.; Kasza, K. E.
NASA Astrophysics Data System (ADS)
Inuit hunters of the North have long recognized ice as the natural state of water from which life flows on Earth. Although unaware of the microscopic world, they chart changes in properties of ice and water that derive from a succession of microbial inhabitants. Scientific hunters of the West have largely overlooked all but the warmest of ices as dynamic scenes of microbial life, considering the frozen realm to archive life forms instead. Deeply frozen glacial ice on Earth does appear to preserve microbes effectively, but isn't the ocean beneath the geologically dynamic ice of Europa believed too salty? Aren't the subsurface ices of Mars expected to be rich in all manner of mineralogical impurities? Wherever salt and other mineral impurities are sufficiently abundant in Earth ice, the ice contains interior liquid water that can range from nano-layer films on grain surfaces (glacial ice) to a porous network of brine (Arctic winter sea ice down to 20�C). Other recent studies of saline ices have indicated a world of interacting life forms, with viruses infecting bacteria in brines at -12�C (the lowest temperature tested), the domains of Bacteria and Archaea undergoing succession in winter ices (down to -28�C), and evidence that cellular maintenance may go forward incrementally even below the eutectic of seawater (-55�C). Microbes are also known to alter the physical properties of their icy homes by producing exopolymers that further depress the freezing point, either directly or by entraining more salt into the ice. Even the most inhospitable of ices to human hunters may contain interior oases for microbes, in control to some degree of their own space. In considering the habitability of icy worlds beyond Earth, we'd do well to learn more about the evolutionary prowess of microbes in adapting to conditions beyond our warm-blooded imaginations.
Deming, Jody
Mountain of Ice: Secrets in the Ice
NSDL National Science Digital Library
This classroom activity has students graph and analyze chemical concentrations from ice core data. They will be analyzing some of the actual data that United States International Trans-Antarctic Scientific Expedition (ITASE) scientists obtained from Antarctica when they drilled into the West Antarctic Ice Sheet to collect ice cores for data on past sulfate, sodium, and chloride ion concentrations. The data will eventually be used to help understand global climate change. This activity has a stated objective, a list of materials, procedure, activity answer, and links for more information.
Antifreeze Protein Binds Irreversibly to Ice
NASA Astrophysics Data System (ADS)
Many organisms are protected from freezing by antifreeze proteins (AFPs), which bind to ice and prevent its growth by a mechanism not completely understood. Although it has been postulated that AFPs would have to bind irreversibly to arrest the growth of an ice crystal bathed in excess liquid water, the binding forces seem insufficient to support such a tight interaction. By putting a fluorescent tag on a fish AFP, we were able to visualize AFP binding to ice and demonstrate, by lack of recovery after photo-bleaching, that it is indeed irreversible. Because even the most avid protein/ligand interactions exhibit reversibility, this finding is key to understanding the mechanism of antifreeze proteins, which are becoming increasingly valuable in cryopreservation and improving the frost tolerance of crops.
Braslavsky, I.; Pertaya, N.; di Prinzio, C. L.; Wilen, L.; Thomson, E.; Wettlaufer, J. S.; Marshall, C. B.; Davies, P. L.
Effect of storage temperature on quality of light and full-fat ice cream.
Ice cream quality is dependent on many factors including storage temperature. Currently, the industry standard for ice cream storage is -28.9 �C. Ice cream production costs may be decreased by increasing the temperature of the storage freezer, thus lowering energy costs. The first objective of this research was to evaluate the effect of 4 storage temperatures on the quality of commercial vanilla-flavored light and full-fat ice cream. Storage temperatures used were -45.6, -26.1, and -23.3 �C for the 3 treatments and -28.9 �C as the control or industry standard. Ice crystal sizes were analyzed by a cold-stage microscope and image analysis at 1, 19.5, and 39 wk of storage. Ice crystal size did not differ among the storage temperatures of light and full-fat ice creams at 19.5 or 39 wk. An increase in ice crystal size was observed between 19.5 and 39 wk for all storage temperatures except -45.6 �C. Coldness intensity, iciness, creaminess, and storage/stale off-flavor of the light and full-fat ice creams were evaluated at 39 wk of storage. Sensory evaluation indicated no difference among the different storage temperatures for light and full-fat ice creams. In a second study, light and full-fat ice creams were heat shocked by storing at -28.9 �C for 35 wk and then alternating between -23.3 and -12.2 �C every 24h for 4 wk. Heat-shocked ice creams were analyzed at 2 and 4 wk of storage for ice crystal size and were evaluated by the sensory panel. A difference in ice crystal size was observed for light and full-fat ice creams during heat-shock storage; however, sensory results indicated no differences. In summary, storage of light or full-fat vanilla-flavored ice creams at the temperatures used within this research did not affect quality of the ice creams. Therefore, ice cream manufacturers could conserve energy by increasing the temperature of freezers from -28.9 to -26.1 �C. Because freezers will typically fluctuate from the set temperature, usage of -26.1 �C allows for a safety factor, even though storage at -23.3 �C did not affect ice cream quality. PMID:21524511
Buyck, J R; Baer, R J; Choi, J
Eutectic freeze crystallization simultaneous formation and separation of two solid phases
NASA Astrophysics Data System (ADS)
Eutectic freeze crystallization (EFC) separates aqueous inorganic solutions into pure water and pure salt. By operating at the eutectic point, ice and salt can be formed simultaneously as two separate phases. Two aqueous systems were investigated in batch and continuous crystallization experiments: copper sulfate (eutectic temperature 271 K) and mono-ammonium phosphate (269 K). Below the eutectic temperature, ice can be formed without any salt formation by seeding with ice seeds and solely salt is formed by seeding with salt crystals. When however, the solution is seeded with both salt and ice crystals, two distinct solid phases are formed: when the stirrer is turned off, ice rises and salt settles. This shows that EFC separates aqueous solutions into ice and salt as two distinct phases. Based on these results, a 15 l cooled disk column crystallizer (CDCC) has been built, designed to crystallize and separate both the solids simultaneously in a single apparatus.
van der Ham, F.; Witkamp, G. J.; de Graauw, J.; van Rosmalen, G. M.
Probing ice clouds by broadband mid-infrared extinction spectroscopy: case studies from ice nucleation experiments in the AIDA aerosol and cloud chamber
NASA Astrophysics Data System (ADS)
Series of infrared extinction spectra of ice crystals were recorded in the 6000-800 cm-1 wavenumber regime during expansion cooling experiments in the large aerosol and cloud chamber AIDA of Forschungszentrum Karlsruhe. Either supercooled sulphuric acid solution droplets or dry mineral dust particles were added as seed aerosols to initiate ice formation after having established ice supersaturated conditions inside the chamber. The various ice nucleation runs were conducted at temperatures between 237 and 195 K, leading to median sizes of the nucleated ice particles of 1-15 �m. The measured infrared spectra were fitted with reference spectra from T-matrix calculations to retrieve the number concentration as well as the number size distribution of the generated ice clouds. The ice particles were modelled as finite circular cylinders with aspect ratios ranging from 0.5 to 3.0. Benefiting from the comprehensive diagnostic tools for the characterisation of ice clouds which are available at the AIDA facility, the infrared retrieval results with regard to the ice particle number concentration could be compared to independent measurements with various optical particle counters. This provided a unique chance to quantitatively assess potential errors or solution ambiguities in the retrieval procedure which mainly originate from the difficulty to find an appropriate shape representation for the aspherical particle habits of the ice crystals. Based on these inter-comparisons, we demonstrate that there is no standard retrieval approach which can be routinely applied to all different experimental scenarios. In particular, the concept to account for the asphericity of the ice crystals, the a priori constraints which might be imposed on the unknown number size distribution of the ice crystals (like employing an analytical distribution function), and the wavenumber range which is included in the fitting algorithm should be carefully adjusted to each single retrieval problem.
Wagner, R.; Benz, S.; M�hler, O.; Saathoff, H.; Schurath, U.
Why Spin Ice Obeys the Ice Rules
The low-temperature entropy of the spin ice compounds, such as Ho2Ti2O7 and Dy2Ti2O7, is well described by the nearest-neighbor antiferromagnetic Ising model on the pyrochlore lattice, i.e., by the ``ice rules.'' This is surprising since the dominant coupling between the spins is their long ranged dipole interaction. We show that this phenomenon can be understood rather elegantly: one can construct
S. V. Isakov; R. Moessner; S. L. Sondhi
Quantum melting of spin ice: emergent cooperative quadrupole and chirality.
Quantum melting of spin ice is proposed for pyrochlore-lattice magnets Pr2TM2O7 (TM=Ir, Zr, and Sn). The quantum superexchange Hamiltonian having a nontrivial magnetic anisotropy is derived on the basis of atomic non-Kramers magnetic doublets. The ground states exhibit a cooperative ferroquadrupole and pseudospin chirality, forming a magnetic analog of smectic liquid crystals. Our theory accounts for dynamic spin-ice behaviors experimentally observed in Pr2TM2O7. PMID:20867877
Onoda, Shigeki; Tanaka, Yoichi
Field demonstration of the ICE 250{trademark} Cleaning System
The ICE 250{trademark} Cleaning System was engineered to convert water into small ice particles for use in cleaning and decontamination applications. Ice crystals are produced in a special icemaker and pressured through a hose-nozzle onto the surface to be cleaned. The Rocky Mountain Oilfield Testing Center and Ice Cleaning Systems, Inc., conducted a test of this system at Naval Petroleum Reserve No. 3 to evaluate the system's cleaning capabilities in an oil field environment. Equipment cleaned included an oil storage tank, a rod pumping unit, a road grader, and a wellhead. Contaminants were unrefined sour crude oil, hydraulic fluid, paraffin, and dirt, occurring separately and as mixtures. In all four demonstration cleaning tasks, the ICE 250 System effectively removed surface contaminant mixtures in a timely manner and left no oily residue. A minimal amount of waste moisture was generated, thereby reducing cleanup and disposal costs.
Johnston, J.L.; Jackson, L.M.
NASA Technical Reports Server (NTRS)
During high Martian obliquity, ice is stable to lower latitudes than predicted by models of present conditions and observed by the Gamma Ray Spectrometer (approx. 60 deg N). An ice-rich layer deposited at mid-latitudes could persist to the present day; ablation of the top 1 m of ice leaving a thin insulating cover could account for lack of its detection by GRS. The presence of an ice-layer in the mid-latitudes is suggested by a network of polygons, interpreted as ice-wedge cracks. This study focuses on an exceptional concentration of polygons in Western Utopia (section of Casius quadrangle, roughly 40 deg - 50 deg N, 255 deg - 300 deg W). We attempt to determine the thickness and age of this ice layer through crater-polygons relations.
McBride, S. A.; Allen, C. C.; Bell, M. S.
NASA Technical Reports Server (NTRS)
The subsurface ice probe (SIPR) is a proposed apparatus that would bore into ice to depths as great as hundreds of meters by melting the ice and pumping the samples of meltwater to the surface. Originally intended for use in exploration of subsurface ice on Mars and other remote planets, the SIPR could also be used on Earth as an alternative to coring, drilling, and melting apparatuses heretofore used to sample Arctic and Antarctic ice sheets. The SIPR would include an assembly of instrumentation and electronic control equipment at the surface, connected via a tether to a compact assembly of boring, sampling, and sensor equipment in the borehole (see figure). Placing as much equipment as possible at the surface would help to attain primary objectives of minimizing power consumption, sampling with high depth resolution, and unobstructed imaging of the borehole wall. To the degree to which these requirements would be satisfied, the SIPR would offer advantages over the aforementioned ice-probing systems.
Hecht, Michael; Carsey, Frank
NSDL National Science Digital Library
This is a lesson about detecting ice on the permanently shadowed craters of Mercury and the Moon. Learners will consider what might be in that ice and will examine why the polar regions of Earth, Mercury and the Moon are colder than elsewhere on the planets. Activities include small group miming, speaking, drawing, and/or writing. This is the lesson 12 of 12 in the unit, Exploring Ice in the Solar System.
Observing cosmic microwave background polarization through ice
Ice crystal clouds in the upper troposphere can generate polarization signals at the muK level. This signal can seriously affect very sensitive ground-based searches for E and B modes of cosmic microwave background polarization. In this paper, we estimate this effect within the ClOVER experiment observing bands (97, 150 and 220 GHz) for the selected observing site (Llano de Chajnantor,
Luca Pietranera; Stefan A. Buehler; Paolo G. Calisse; Claudia Emde; Darren Hayton; Viju Oommen John; Bruno Maffei; Lucio Piccirillo; Giampaolo Pisano; Giorgio Savini; T. R. Sreerekha
A method is provided for constructing spray ice barriers to protect offshore structures in a frigid body of water from mobile ice, waves and currents. Water is withdrawn from the body of water and is sprayed through ambient air which is below the freezing temperature of the water so that a substantial amount of the water freezes as it passes through the air. The sprayed water is directed to build up a mass of ice having a size and shape adapted to protect the offshore structure. Spray ice barriers can also be constructed for the containment of pollutant spills.
Finucane, R. G.; Jahns, H. O.
We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.
Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.
A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.
Peltier, W.R. (Univ. of Toronto, Ontario (Canada))
NASA Astrophysics Data System (ADS)
We describe the design of an instrument that can fully implement a new nanopatterning method called ice lithography, where ice is used as the resist. Water vapor is introduced into a scanning electron microscope (SEM) vacuum chamber above a sample cooled down to 110 K. The vapor condenses, covering the sample with an amorphous layer of ice. To form a lift-off mask, ice is removed by the SEM electron beam (e-beam) guided by an e-beam lithography system. Without breaking vacuum, the sample with the ice mask is then transferred into a metal deposition chamber where metals are deposited by sputtering. The cold sample is then unloaded from the vacuum system and immersed in isopropanol at room temperature. As the ice melts, metal deposited on the ice disperses while the metals deposited on the sample where the ice had been removed by the e-beam remains. The instrument combines a high beam-current thermal field emission SEM fitted with an e-beam lithography system, cryogenic systems, and a high vacuum metal deposition system in a design that optimizes ice lithography for high throughput nanodevice fabrication. The nanoscale capability of the instrument is demonstrated with the fabrication of nanoscale metal lines.
Han, Anpan; Chervinsky, John; Branton, Daniel; Golovchenko, J. A.
Expression and Characterization of an Ice Binding Protein from a Bacterium Isolated at a Depth of 3,519 Meters in the Vostok Ice Core, Antarctica
NASA Astrophysics Data System (ADS)
The cryopreservation of microorganisms in ancient glacial ice is possible if lethal levels of macromolecular damage are not incurred and cellular integrity is not compromised via intracellular ice formation or recrystallization. There are numerous examples of cold-adapted species that prevent or limit ice crystal growth by producing ice-binding proteins (IBP). Previously, a bacterium (isolate 3519-10; Flavobacteriaceae family) recovered from a depth of 3,519 meters below the surface in the Vostok ice core was shown to produce and secrete an IBP that inhibits the recrystallization of ice. To explore the phenotypic advantage that IBPs confer to ice-entrapped cells, experiments were designed to examine the expression of 3519-10's IBP gene and protein at different temperatures, assess the effect of the IBP on bacterial viability in ice, and determine how the IBP influences the physical structure of the ice. Total RNA isolated from aerobic cultures grown at temperatures between 4C to 25C and analyzed by reverse transcription-PCR indicated constitutive expression of the IBP gene. Additionally, SDS-PAGE analysis of 3519-10's extracellular proteins revealed a polypeptide corresponding to the predicted size of the 54 kDa IBP at all temperatures tested. The total extracellular protein fraction was subsequently used in assays with Escherichia coli to examine the effect of the IBP on bacterial survival in warm ice (-5C) and after freeze-thaw cycling. In the presence of 100 ?g mL-1 of extracellular protein from 3519-10, the survival of E. coli was increased by greater than 100-fold; however, the survival of E. coli suspensions containing the same concentration of bovine serum albumin was not significantly different than controls (p<0.05). Microscopic analysis of ice formed in the presence of the IBP indicated that in a mm^2 field of view, there were 5 times as many crystals as in ice formed in the presence of washed 3519-10 cells and non-IBP producing bacteria, and 10 times as many crystals as in particle-free deionized water. Presumably, the effect that the IBP has on bacterial viability and ice crystal structure is due to its activity as an inhibitor of ice recrystallization. Although a myriad of molecular adaptations are likely to play a role in bacterial persistence under frozen conditions, the ability of 3519-10's IBP to control ice crystal structure may provide one explanation for its successful survival deep within the Antarctic ice sheet for thousands of years.
Christner, B. C.; Achberger, A.; Brox, T. I.; Skidmore, M. L.
Pre- and post-thaw assessment of intracellular ice formation.
Intracellular ice formation (IIF) refers to the formation of ice crystals within cells during rapid freezing. To develop an understanding of the means by which intracellular ice forms and the mechanisms by which it damages cells and tissues requires techniques that combine real-time assessment of ice nucleation and ice crystal growth with detailed assessments of cell structure and function. Intracellular ice formation has been detected in live samples using light scattering, freeze substitution and fluorescent detection. In this study we develop a method to correlate IIF with post-thaw structural analyses by combining low temperature microscopy and freeze substitution. V79-4 hamster fibroblasts were frozen on a low temperature microscope at various temperatures, IIF was visualized using the nucleic acid-specific fluorophore SYTO 13, then the samples were fixed (10% formaldehyde, 85% ethanol, 5% acetic acid) while still frozen. The monolayers were then thawed and stained with routine histological stains haematoxylin and eosin and assessed. Fixation allowed for the post-thaw assessment of IIF and for subsequent histological processing to examine in detail the structural consequences of IIF. The post-thaw identification of cells that form intracellular ice during freezing is a significant improvement to current methods used in low temperature biology. PMID:15315499
Acker, J P; Croteau, I M
Application of Ice Nucleation Kinetics in Orographic Clouds.
NASA Astrophysics Data System (ADS)
Ice nucleation by silver iodide-sodium iodide aerosol particles has been characterized in the Colorado State University isothermal cloud chamber using the techniques of chemical kinetics. Two separate mechanisms of condensation-freezing ice nucleation have been observed. One mechanism occurs at water saturation and is a characteristically slow process, with a half-life of the order of 10-30 min. The other mechanism occurs when the environment is supersaturated with respect to liquid water. This mechanism is characteristically fast, requires less than a minute for completion, and results in a higher yield of ice crystals than the slow mechanism.The mechanism, rate and yield data obtained in the laboratory investigations are applied to an orographic cloud particle trajectory model to assess the ice nucleation characteristics of silver iodide-sodium iodide aerosol particles in the temporal and spatial scale of an orographic cloud. The importance of nucleation mechanism, rate and yield are investigated to determine the control these parameters have on the extent and location of ice nucleation within the cloud and the effect on precipitation distribution. In certain conditional ice crystal production was found to be prolonged over time and space. Resulting precipitation occurred over large areas. In other conditions, ice nucleation occurred primarily within a zone of a few kilometers. Precipitation was then found to occur in a more restricted area. The mechanism and rates of nucleation therefore can affect the targeting and analysis of seeding effects in weather modification experiments.
Blumenstein, Rochelle R.; Rauber, Robert M.; Grant, Lewis O.; Finnegan, William G.
The Far Infrared Spectrum and Long-Range Forces in Ice.
National Technical Information Service (NTIS)
Ice I is an example of a crystal in which the molecules are arranged nearly regularly in a crystal lattice, but are orientationally disordered. The orientational disorder results in all the translational vibrations of the crystal being active in both infr...
E. Whalley J. E. Bertie
Experimental Studies of the Crystallization of Supercooled Water
The crystal fabric of ice formed by the freezing of supercooled water was examined in polarized light. Drops of radius 0.1 cm were frozen by homogeneous nucleation at 33C, by various foreign particles in suspension, or by impaction on a plane single crystal ice substrate. Bulk water, volume about 1.0 cm3, was frozen by the insertion of a single crystal
J. Hallett
New insights into ice growth and melting modifications by antifreeze proteins
Antifreeze proteins (AFPs) evolved in many organisms, allowing them to survive in cold climates by controlling ice crystal growth. The specific interactions of AFPs with ice determine their potential applications in agriculture, food preservation and medicine. AFPs control the shapes of ice crystals in a manner characteristic of the particular AFP type. Moderately active AFPs cause the formation of elongated bipyramidal crystals, often with seemingly defined facets, while hyperactive AFPs produce more varied crystal shapes. These different morphologies are generally considered to be growth shapes. In a series of bright light and fluorescent microscopy observations of ice crystals in solutions containing different AFPs, we show that crystal shaping also occurs during melting. In particular, the characteristic ice shapes observed in solutions of most hyperactive AFPs are formed during melting. We relate these findings to the affinities of the hyperactive AFPs for the basal plane of ice. Our results demonstrate the relation between basal plane affinity and hyperactivity and show a clear difference in the ice-shaping mechanisms of most moderate and hyperactive AFPs. This study provides key aspects associated with the identification of hyperactive AFPs.
Bar-Dolev, Maya; Celik, Yeliz; Wettlaufer, J. S.; Davies, Peter L.; Braslavsky, Ido
AMSR-E Arctic Sea Ice: September 2010 to March 2011: Scientists tracking the annual maximum extent of Arctic sea ice said that 2011 was among the lowest ice extents measured since satellites began ...
Near-infrared spectral monitoring of Pluto's ices II: Recent decline of CO and N2 ice absorptions
NASA Astrophysics Data System (ADS)
IRTF/SpeX observations of Pluto's near-infrared reflectance spectrum during 2013 show vibrational absorption features of CO and N2 ices at 1.58 and 2.15 ?m, respectively, that are weaker than had been observed during the preceding decade. To reconcile declining volatile ice absorptions with a lack of decline in Pluto's atmospheric pressure, we suggest these ices could be getting harder to see because of increasing scattering by small CH4 crystals, rather than because they are disappearing from the observed hemisphere.
Grundy, W. M.; Olkin, C. B.; Young, L. A.; Holler, B. J.
NASA Technical Reports Server (NTRS)
The Aviation Safety Program initiated by NASA in 1997 has put greater emphasis in safety related research activities. Ice-contaminated-tailplane stall (ICTS) has been identified by the NASA Lewis Icing Technology Branch as an important activity for aircraft safety related research. The ICTS phenomenon is characterized as a sudden, often uncontrollable aircraft nose- down pitching moment, which occurs due to increased angle-of-attack of the horizontal tailplane resulting in tailplane stall. Typically, this phenomenon occurs when lowering the flaps during final approach while operating in or recently departing from icing conditions. Ice formation on the tailplane leading edge can reduce tailplane angle-of-attack range and cause flow separation resulting in a significant reduction or complete loss of aircraft pitch control. In 1993, the Federal Aviation Authority (FAA) and NASA embarked upon a four-year research program to address the problem of tailplane stall and to quantify the effect of tailplane ice accretion on aircraft performance and handling characteristics. The goals of this program, which was completed in March 1998, were to collect aerodynamic data for an aircraft tail with and without ice contamination and to develop analytical methods for predicting the effects of tailplane ice contamination. Extensive dry air and icing tunnel tests which resulted in a database of the aerodynamic effects associated with tailplane ice contamination. Although the FAA/NASA tailplane icing program generated some answers regarding ice-contaminated-tailplane stall (ICTS) phenomena, NASA researchers have found many open questions that warrant further investigation into ICTS. In addition, several aircraft manufacturers have expressed interest in a second research program to expand the database to other tail configurations and to develop experimental and computational methodologies for evaluating the ICTS phenomenon. In 1998, the icing branch at NASA Lewis initiated a second multi-phase research program for tailplane icing (TIP II) to develop test methodologies and tailplane performance and handling qualities evaluation tools. The main objectives of this new NASA/Industry/Academia collaborative research programs were: (1) define and evaluate a sub-scale wind tunnel test methodology for determining tailplane performance degradation due to icing. (2) develop an experimental database of tailplane aerodynamic performance with and without ice contamination for a range of tailplane configurations. Wind tunnel tests were planned with representative general aviation aircraft, i.e., the Learjet 45, and a twin engine low speed aircraft. This report summarizes the research performed during the first year of the study, and outlines the work tasks for the second year.
Eutectic freeze crystallization: Application to process streams and waste water purification
Two case studies are presented using eutectic freeze crystallization (EFC) as an alternative for evaporative crystallization: a 7.8 ton day?1 35 w% aqueous sodium nitrate and a 24 ton day?1 12 w% copper sulfate stream. The proposed crystallizer is a cooled disk column crystallizer (CDCC), using indirect cooling for heat transfer. In single stage operation, the formed ice crystals are
F. van der Ham; G. J. Witkamp; J. de Graauw; G. M. van Rosmalen
Artic ice and drilling structures
The sea ice in the southern Beaufort Sea is examined and subdivided into three zones: the fast ice zone, the seasonal pack-ice zone, an the polar pack ice zone. Each zone requires its own type of system. Existing floating drilling systems include ice-strengthened drill ships, conical drilling systems, and floating ice platforms in deep-water land-fast ice. The development of hydrocarbon resources in the Arctic presents great challenges to engineers, since the structures are required to operate safely under various conditions. Significant progress has yet to be made in understanding the behavior of ice.
Sodhl, D.S.
Deposition Ice Nuclei Concentration at Different Temperatures and Supersaturations
NASA Astrophysics Data System (ADS)
Ice formation is one of the main processes involved in the initiation of precipitation. Some aerosols serve to nucleate ice in clouds. They are called ice nuclei (IN) and they are generally solid particles, insoluble in water. At temperatures warmer than about -36�C the only means for initiation of the ice phase in the atmosphere involves IN, and temperature and supersaturation required to activate IN are considered as key information for the understanding of primary ice formation in clouds. The objective of this work is to quantify the IN concentration at ground level in C�rdoba City, Argentina, under the deposition mode, that is to say that ice deposits on the IN directly from the vapor phase. It happens when the environment is supersaturated with respect to ice and subsaturated with respect to liquid water. Ice nuclei concentrations were measured in a cloud chamber placed in a cold room with temperature control down to -35�C. The operating temperature was varied between -15�C and -30�C. Ice supersaturation was ranged between 2 and 20 %. In order to quantify the number of ice particles produced in each experiment, a dish containing a supercooled solution of cane sugar, water and glycerol was placed on the floor of the cloud chamber. The activated IN grew at the expense of vapor until ice crystals were formed and these then fell down onto the sugar solution. Once there, these crystals could grow enough to be counted easily with a naked eye after a period of about three minutes, when they reach around 2 mm in diameter. In order to compare the present results with previously reported results, the data were grouped in three different ranges of supersaturation: the data with supersaturations between 2 and 8 %, the data with supersaturations between 8 and 14% and the data with supersaturations between 14 and 20 %. In the same way, in order to analize the behavior of IN concentration with supersaturation, the data were grouped for three different temperatures, the data with temperatures between -15�C and -20�C, the data with temperatures between -20�C and -25�C and the data with temperatures between -25�C and -30�C. The results confirm that for each temperature range, the concentration of IN increases at higher supersaturation, and show the tendency of the IN concentration to increase with increasing ice supersaturation. Based on previous parameterizations, a combination of IN concentration in relation with temperature and ice supersaturation is proposed in this work. As far as we know, this is among the first work to measure and parameterize the concentration of deposition ice nuclei in the Southern Hemisphere.
L�pez, M. L.; Avila, E.
ERIC Educational Resources Information Center
Explains an activity in which students construct a simulated ice core. Materials required include only a freezer, food coloring, a bottle, and water. This hands-on exercise demonstrates how a glacier is formed, how ice cores are studied, and the nature of precision and accuracy in measurement. Suitable for grades three through eight. (Author/PVD)
Kopaska-Merkel, David C.
NSDL National Science Digital Library
In this activity about the solar system, learners use various light sources to examine ice with different components to understand how NASA studies planets and moons from space. This detailed lesson guide includes background information about distant ice worlds in the outer solar system, literature connections, instructions for a pre-activity demonstration, modified activities by age, tips, discussion questions, and resources.
Education, Carnegie I.
A volcano discovered six years ago by researchers Blankenship and Bell under Antarctica poses questions about a potential climatic catastrophe. The researchers claim that the volcano is still active, erupting occasionally and growing. A circular depression on the surface of the ice sheet has ice flowing into it and is used to provide a portrait of the heat source. The volcano is on a critical transition zone within West Antarctica with fast flowing ice streams directly downhill. Work by Blankenship shows that a soft layer of water-logged sediments called till provide the lubricating layer on the underside of the ice streams. Volcanos may provide the source of this till. The ice streams buffer the thick interior ice from the ocean and no one know what will happen if the ice streams continue to shorten. These researchers believe their results indicate that the stability of West Antarctica ultimately depends less on the current climate than on the location of heat and sediments under the ice and the legacy of past climatic changes.
Monastersky, R.
ERIC Educational Resources Information Center
This experimental edition provides a number of activities useful for investigating snow and ice with elementary school children. Commencing with games with ice cubes, the activities lead through studies of snowflakes, snowdrifts, effects of wind and obstacles on the shape and formation of drifts, to a study of animals living under snow. The�
Minneapolis Independent School District 275, Minn.
National Technical Information Service (NTIS)
This report describes laboratory tests to determine the effectiveness of a copolymer coating on a balloon to minimize ice build-up problems when operating in sleet, freezing rain or other ice-forming conditions. Methods for deicing the surface after an ic...
B. Hanamoto
National Technical Information Service (NTIS)
This report summarises the issues related to the use of man-made ice islands as exploration drilling structures in the Canadian Arctic Islands and Beaufort Sea. The historical development of ice island technology has been reviewed with respect to design, ...
NSDL National Science Digital Library
This animation shows the retreat of glacial ice, changes in the shoreline, and the disappearance of the land bridge across the Bering Sea which occurred at the end of the last ice age, beginning just over 21,000 years ago.
NSDL National Science Digital Library
What can glaciers tell us about volcanoes and atmospheric conditions? How does this information relate to our understanding of climate change? Ice Core Investigations is an original and innovative activity that explores these types of questions. It brings together popular science issues such as research, climate change, ice core drilling, and air pollution to create a meaningful science learning experience for students.
Krim, Jessica; Brody, Michael
Artificial spin ice arrays of micromagnetic islands are a means of engineering additional energy scales and frustration into magnetic materials. Here we demonstrate a magnetic phase transition in an artificial square spin ice and use the symmetry of the lattice to verify the presence of excitations far below the ordering temperature. We do this by measuring the temperature-dependent magnetization in
Vassilios Kapaklis; Unnar B Arnalds; Adam Harman-Clarke; Evangelos Th Papaioannou; Masoud Karimipour; Panagiotis Korelis; Andrea Taroni; Peter C W Holdsworth; Steven T Bramwell; Bj�rgvin Hj�rvarsson
Recently, significant interest has emerged in fabricated systems that mimic the behavior of geometrically-frustrated materials. Here, I will present the full realization of such an artificial spin ice system on a two-dimensional kagome lattice, and I will present results obtained by directly counting individual pseudospins, demonstrating rigid adherence to the local ice rule. This adherence is maintained even when the
John Cumings
A new optical ice particle counter at LACIS
NASA Astrophysics Data System (ADS)
Clouds play an important role within the climate system, especially for the radiative energy budget of the earth. The radiative properties of a cloud depend strongly on the fractions of ice crystals and water droplets, their size distributions, and the ice crystal shapes within the particular cloud. One option to gain this kind of information is using optical particle counters. A new optical particle counter is developed for laboratory work and is based on the concept of the Thermostabilized Optical Particle Spectrometer for the Detection of Ice Particles (TOPS-Ice, Clauss et al., 2013). TOPS-Ice uses linearly polarized green laser light and the depolarization of the scattered light at a scattering angle of 42.5� to discriminate between liquid water droplets and ice crystals in the lower ?m range. However, the measurements are usually limited to ice fractions in the order of 1%. To improve the determination of the ice fraction, several modifications of the original setup are implemented including an additional detection system at another scattering angle. The new scattering angle is optimized for least interference between the droplet and ice signals. This is achieved by finding the angle with the maximum difference in scattered intensity of water droplets compared to ice crystals with the same volume equivalent diameter. The suitable scattering angle of 100� for linearly polarized light was chosen based on calculations using T-Matrix method, Lorenz-Mie theory, M�ller matrices and distribution theory. The new optical setup is designed to run in combination with a laminar flow tube, the so-called Leipzig Aerosol Cloud Interaction Simulator (LACIS, Stratmann et al., 2004; Hartmann et al., 2011). Using LACIS and its precisely controlled thermodynamic conditions, we are able to form small water droplets and ice crystals which will then be detected, classified and sized by our new optical device. This setup is planned to be tested in ice measurements including Snomax� and several dusts (e.g. illite, kaolinite, ATD) as ice nuclei which all show different behaviors in ice formation. Furthermore, a detailed comparison of both instruments TOPS-Ice and the new setup is planned. This project is part of the Leipzig Graduate School on Clouds, Aerosols and Radiation and is partly supported by the German Research Foundation (DFG project WE 4722/1-1) within the DFG Research Unit FOR 1525 INUIT. Clauss, T., Kiselev, A., Hartmann, S., Augustin, S., Pfeifer, S., Niedermeier, D., Wex, H., and Stratmann, F, 2013, Application of linear polarized light for the discrimination of frozen and liquid droplets in ice nucleation experiments, Atmos. Meas. Tech., 6, 1041-1052. Hartmann, S., Niedermeier, D., Voigtl�nder, J., Clauss, T., Shaw, R. A., Kiselev, A., and Stratmann, F., 2011, Homogeneous and heterogeneous ice nucleation at LACIS: operating principle and theoretical studies, Atmos. Chem. Phys., 11, 1753-1767. Stratmann, F., Kiselev, A., Wurzler, S., Wendisch, M., Heintzenberg, J., Charlson, R. J., Diehl, K., Wex, H., and Schmidt, S., 2004, Laboratory Studies and Numerical Simulations of Cloud Droplet Formation under Realistic Supersaturation Conditions, J. Atmos. Oceanic. Technol., 21, 876-887.
Bieligk, Henner; Voelker, Georg Sebastian; Clauss, Tina; Grundmann, Marius; Stratmann, Frank
Einstein equations in the null quasi-spherical gauge III: numerical algorithms
We describe numerical techniques used in the construction of our 4th order\\u000aevolution for the full Einstein equations, and assess the accuracy of\\u000arepresentative solutions. The code is based on a null gauge with a\\u000aquasi-spherical radial coordinate, and simulates the interaction of a single\\u000ablack hole with gravitational radiation. Techniques used include spherical\\u000aharmonic representations, convolution spline interpolation and
Robert A. Bartnik; Andrew H. Norton
Quasi-spherical solid polymer membranes in separation chemistry: polyurethane foams as sorbents. Recent advances
The advances in using polyurethane foam sorbents for chemical preconcentrations and separations are systematized and reviewed for the 1983�1988 period. The new achievements are ordered in tables split according to the status of the polyurethane foam sorbent i.e. untreated membranes, swollen membranes and membranes modified by chemical anchoring, and to the phase from which the separation or preconcentration is achieved
T. Braun
Measurements of natural deposition ice nuclei in C�rdoba, Argentina
NASA Astrophysics Data System (ADS)
Ice nucleation in the atmosphere is of practical and fundamental importance since ice crystals influence the release of snow, rain and hail. Suspended aerosols in the atmosphere typically initiate freezing at temperatures below -15 �C; although occasionally freezing occurs at higher temperatures. In this work we describe an experimental device designed to measure the concentration of natural ice nuclei under controlled temperature and supersaturation conditions. The measurements were performed at C�rdoba City, for temperatures between -15 �C and -30 �C and the sampled air was supersaturated with respect to ice and subsaturated with respect to liquid water; under these conditions the deposition ice nuclei were quantified. There are few studies reported in the literature regarding measurements of deposition ice nuclei concentration and, to our knowledge, there are no previous laboratory data of this kind of ice nuclei for T < -20 �C. The results show that the number of deposition ice nuclei increases at colder temperatures and higher supersaturations. These results are in general in good agreement with results previously reported by other authors. A fitting function which depends on temperature and supersaturation is proposed to parameterize the results obtained in the present work.
L�pez, M. L.; �vila, E. E.
NASA Astrophysics Data System (ADS)
Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS-MLS, CloudSat-CPR and CALIOP-CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.
Mill�N, L.; Read, W.; Kasai, Y.; Lambert, A.; Livesey, N.; Mendrok, J.; Sagawa, H.; Sano, T.; Shiotani, M.; Wu, D. L.
NSDL National Science Digital Library
This site features a video that illustrates both seasonal patterns and long-term changes in sea ice distribution across the Arctic Ocean. It draws data from two satellite instruments that measure emitted microwave radiation, which helps distinguish open ocean from ice. It shows that during the winter months, a layer of ice forms across vast expanses of the Arctic Ocean and each summer, more than half of that ice vanishes. Students discover that this natural cycle of freezing and thawing is influenced both by seasonal temperature variations and long-term climate change and that scientists are using satellite images to measure the distribution of Arctic sea ice in order to gain a better understanding of how it is linked to Earth's climate system.
The silver-blue cloudlets again - Nucleation and growth of ice in the mesosphere
NASA Astrophysics Data System (ADS)
The existence of noctilucent clouds probably indicates that there are submicron ice crystals in the upper atmosphere at altitudes of 80-85 km. For ice crystals to form at all, the temperature in the cloud region must be very low. The pressure at these heights is such that the ice crystals have relatively large settling speeds and growth has to be rapid enough for the crystals to reach observable size before they drop clear of the saturated region. The mesosphere is thought to be rather dry, with water vapor mixing ratios of a few parts per million only and it becomes difficult to envisage conditions where the growth rate is large enough to give crystals of observable size. In this paper, the results of numerical calculations of crystal sizes are discussed to provide a guide to the interpretation of observational data.
Gadsden, M.
NASA Technical Reports Server (NTRS)
The Shuttle Ice Liberation Coating (SILC) has been developed to reduce the adhesion of ice to surfaces on the space shuttle. SILC, when coated on a surface (foam, metal, epoxy primer, polymer surfaces), will reduce the adhesion of ice by as much as 90 percent as compared to the corresponding uncoated surface. This innovation is a durable coating that can withstand several cycles of ice growth and removal without loss of anti-adhesion properties. SILC is made of a binder composed of varying weight percents of siloxane(s), ethyl alcohol, ethyl sulfate, isopropyl alcohol, and of fine-particle polytetrafluoroethylene (PTFE). The combination of these components produces a coating with significantly improved weathering characteristics over the siloxane system alone. In some cases, the coating will delay ice formation and can reduce the amount of ice formed. SILC is not an ice prevention coating, but the very high water contact angle (greater than 140 ) causes water to readily run off the surface. This coating was designed for use at temperatures near -170 F (-112 C). Ice adhesion tests performed at temperatures from -170 to 20 F (-112 to -7 C) show that SILC is a very effective ice release coating. SILC can be left as applied (opaque) or buffed off until the surface appears clear. Energy dispersive spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS) data show that the coating is still present after buffing to transparency. This means SILC can be used to prevent ice adhesion even when coating windows or other objects, or items that require transmission of optical light. Car windshields are kept cleaner and SILC effectively mitigates rain and snow under driving conditions.
Smith, Trent; Prince, Michael; DwWeese, Charles; Curtis, Leslie
Tensile properties of impact ices
NASA Technical Reports Server (NTRS)
A special test apparatus was developed to measure the tensile strength of impact ices perpendicular to the direction of growth. The apparatus consists of a split tube carefully machined to minimize the effect of the joint on impact ice strength. The tube is supported in the wind tunnel by two carefully aligned bearings. During accretion the tube is turned slowly in the icing cloud to form a uniform coating of ice on the split tube specimen. The two halves of the split tube are secured firmly by a longitudinal bolt to prevent relative motion between the two halves during ice accretion and handling. Tensile test strength results for a variety of icing conditions were obtained. Both glaze and rime ice conditions were investigated. In general, the tensile strength of impact ice was significantly less than refrigerator ice. Based on the limited data taken, the median strength of rime ice was less than glaze ice. However, the mean values were similar.
Chu, M. L.; Scavuzzo, R. J.; Kellackey, C. J.
Decoupling of ice production and ice extent in seasonally ice covered marginal seas
NASA Astrophysics Data System (ADS)
While the seasonally ice covered marginal seas are ice free in the summer, there may be substantial production and transport of ice during the winter. The predominant ice types in these seas are frazil/grease ice, pancake ice and thin sheet ice. Relative production of the different ice types has a dramatic effect on the amount of brine production and the local energy exchange rate between the ocean and the atmosphere. We have developed a model which utilizes daily observations of SMMR and SSM/I microwave radiometers to track the volume and areal ice concentrations of each ice type; allowing us to evaluate the contribution of each ice type to the ice mass, salt, and fresh water redistribution. From this framework, we have calculated the spatial distribution of the annual net salt and fresh water flux to the Bering Sea over a 15 year period. The results indicate there may be a de-coupling between sea ice coverage and sea ice production for the Bering Sea, with the ice production being much less variable than the sea ice coverage. These results are interesting because, to first order, ice production is not responsive to variability in atmospheric forcing from year to year. In this paper, we will discuss the relative importance of different causal mechanisms, and examine linkages and feedbacks between the sea ice, ocean and atmosphere.
Pruis, M.; Toudal, L.; Coon, M. D.
Experiments on planetary ices at UCL
NASA Astrophysics Data System (ADS)
Using a suite of techniques and equipment, we conduct several different types of experiments on planetary ices at UCL. Samples are prepared in the Ice Physics Laboratory, which consists of a 5 chamber complex of inter-connected cold rooms, controllable from +30 to -30 deg C. Within this laboratory we have a functioning triaxial deformation cell operating at low temperature (down to -90 deg C) and high pressures (300 MPa), an Automatic Ice Fabric Analyser (AIFA) and a low-temperature microscope with CCD output. Polycrystalline samples, 40mm diameter by 100mm long, are compressed in the triaxial rig with a confining pressure; single crystal specimens are compressed in a separate uniaxial creep rig which operates at zero confining pressure for surface studies. A cold stage is also available for study of ice microstructural studies on our new Jeol JSM-6480LV SEM, which also allows tensile, compression and/or bending tests, with load ranges from less than 2N to 5000N. Finally, we also use a cold stage on a new PANalytical, X'pert PRO MPD, high resolution powder diffractometer to study the structure and phase behaviour of icy materials. Recent highlights of our work include: (1) derivation of a manufacturing process for methane clathrate at low temperatures, analysed in the X-Ray Diffraction Laboratory, for future rheological experiments, (2) analysed the growth behaviour of MS11, (3) refurbished and commenced calibration tests on the triaxial deformation cell using ice Ih, and (4) performed creep tests on gypsum and epsomite using the single crystal deformation cell. Further experiments will build on these preliminary results.
Grindrod, P. M.; Fortes, A. D.; Wood, I. G.; Dobson, D.; Sammonds, P. R.; Stone-Drake, L.; Vocadlo, L.