we report initial observations of ring current ionswe show that he - ion decay rates are consistent with theorywe show that o - ions with energies greater than 500 kev decay very rapidly we report initial observations of ring current ions we show that he - ion decay rates are consistent with theory we show that o - ions with energies greater than 500 kev decay very rapidly measurements by the radiation belt storm probes ion composition experiment ( rbspice ) instrument [ mitchell et al . , 2013 ] provide the opportunity to examine the compositional changes of the earth 's ring current ( i.e. , energy greater than 10 kev and less than 1 mev ) during geomagnetically disturbed times . these measurements on the van allen probes are the first long - term sets of composition data since the early 1990s that have been made in the inner magnetosphere near the geomagnetic equator and thus can define the magnetospheric response and the compositional changes in the particle energy range that make up ring current populations [ mauk et al . systematic studies of inner magnetospheric h - ion , he - ion , and o - ion ring current abundances and their variations during quiet and moderately active times are relatively scarce , e.g. , on active magnetosphere particle tracer explorer / cce [ daglis et al . , 1993 ; sheldon and hamilton , 1993 ] and crres / magnetospheric ion composition spectrometer [ fu et al . , though an extensive literature exists on the composition of the ring current and higher - energy trapped particle populations during geomagnetic storm conditions ( e.g. , review by keika et al .   and papers therein ) , it is difficult to find absolute flux measurements in these particular energy ranges ( e.g. , review by daglis et al .   and papers therein ) . similarly , reports of he - ion / h - ion abundance ratios ( i.e. , hereafter the he / h ratio ) and o - ion / h - ion abundance ratios ( i.e. , hereafter the o / h ratio ) are likewise scarce at these energy ranges [ e.g. , krimigis and van allen , 1967 ; fritz and krimigis , 1969 ; konradi et al . , 1973 ; gloeckler et al . , 1985 ; hamilton et al . , 1988 ; kistler et al . , 1989 ; fu et al . , 2001 ; pulkkinen et al . , 2001 ; fu et al . , 2003 ; kronberg et al . , 2012 ] . of unique interest in contemporary ring current studies is the physical nature of loss mechanisms . coulomb interactions ( i.e. , drag and scattering ) , charge exchange , drift / convective loss , and wave - particle interactions all play a role in particle loss , with each mechanism being present or even dominant at particular particle energies , particular particle masses , or particular spatial locations [ ebihara and ejiri , 2003 ] . between 50 and 1000 kev , the dominant loss mechanism present for ring current ions is likely charge exchange . in this paper h - ion ( 45 kev to 600 kev ) , he - ion ( 65 kev to 520 kev ) , and o - ion ( 140 kev to 1130 kev ) abundance results from the rbspice instrument , all from van allan probes spacecraft b , are reported . these abundance values are used to show injection ( i.e. , sudden transport into the inner magnetosphere ) and loss characteristics via the he / h ratio and o / h ratio values . we pay particular attention to the observation of a rapid o / h ratio decay which has not been previously reported and does not fit the expected charge exchange paradigm . measurements of h - ion , he - ion , and o - ion fluxes are derived from the time of flight and total energy capabilities of the rbspice instrument [ mitchell et al . , 2013 ] . specifically , ion velocities are determined by measuring the flight time of the particle between collisions with an entrance and exit foil . each foil collision generates secondary electrons which are time - stamped by a microchannel plate . after passing through the last foil six such independent channels ( i.e. ,  telescopes ,  or independent fields - of - view ) exist on the rbspice instrument which , when combined with the spin of the spacecraft , give full pitch angle coverage . the fluxes reported herein are integrated over all pitch angles and over the total energy ranges quoted above . this was done so as to explore the full species flux , which has relevance to the dst index value and solar wind influx . figure 1 shows the species energy ranges and typical fluxes ( particles/(s cm kev ) ) at a dipole l shell 5.5 . we note that he - ions are largely composed of he , though some he could be present in the most extreme of storm events . the presence of he should not be an issue herein , given the fast rate of conversion of he to he . o - ions are expected to be all o. all measurements shown here are well above the instrument noise floor and are statistically significant , as based on poisson counting statistics . rbspice energy ranges for the protons ( black trace ) , he - ions ( red trace ) , and o - ions ( blue trace ) , along with typical integrated flux values ( particles/(s cm kev ) ) at a dipole l shell of 5.5 . he - ion and o - ion flux values are multiplied by 100 for comparative purposes . the vertical bars indicate the region of common energies , 140 kev to 520 kev . in figure 2 we show the measured h - ion , he - ion , and o - ion fluxes ( particles/(s cm ) ) as functions of time and dipole l shell during the first nine mission months following commissioning of the rbspice instrument . these fluxes are obtained using 30 min duration and 0.1 dipole l shell binned data realizations . we note that such temporal bins smear - enhanced flux values often observed during injection events which can occur on the timescale of minutes . we also note that the rbspice instrument was shut off below l3 to reduce anomalous currents and instrument alarming . the hourly dst index is plotted in the top panel for reference . during the time interval shown in figure 2 , the apogee of the van allen probes precessed from 6 magnetic local time ( mlt ) to 17 mlt ( i.e. , from the dawnside , through the night , and toward the duskside ) near the equatorial plane . figure 3 shows four orbit snapshots in the gse coordinate system over the time span of figure 2 . ( first panel ) hourly dst values as reported by the world data center ( wdc ) for geomagnetism , kyoto , japan . ( second to fourth panels ) h - ion ( between the 45 kev to 600 kev energy range ) , he - ion ( between the 65 kev to 520 kev energy range ) , and o - ion ( between the 140 kev to 1130 kev energy range ) flux ( particles/(s cm ) ) , respectively , as measured by the rbspice instrument aboard the van allan probes spacecraft b , binned into 30 min , 0.1 l shell realizations . the rbspice instrument was shut off below l3 to reduce anomalous currents and instrument alarming . orbital plots in the gse x - y plane for four sample times spanning figure 2 . day of year is listed in the upper right - hand corner of each panel . most clearly observed is the enhancement of the flux across all ionic species during active periods , as measured by drops in the dst ( e.g. , on day of year 18 , 28 , 76 , 120 , and 150 ) . this correlation with dst is not unexpected , as the dst is fundamentally a measure of the ring current to which these particles make up . such characteristics are best observed via the ion ratios described next . at the end of this paper we comment on other features observed in figure 2 ( and figure 4 ) . ( top ) hourly dst values as reported from the wdc for geomagnetism , kyoto , japan . ( middle ) time / l shell distribution of the he - ion / h - ion ratio . ( bottom ) time / l shell distribution of the o - ion / h - ion ratio . ratios are calculated from the flux values of figure 2 across the entire energy range of figure 1 . in figure 4 we plot the he / h and the o / h ratios , respectively , along with hourly dst . the ratios are formed using the native energy ranges listed above and are not over a jointly common energy range ( i.e. , 140 kev to 520 kev ) , in an effort to report total ring current ion abundance . with an energy of 100 kev , the predicted charge exchange lifetimes of h - ions at an l shell of 5 and 3.5 are 20 days and 4.5 days , respectively , and are therefore much longer than the predicted / observed charge exchange decay rates of he - ions and o - ions at these energies [ daglis et al . , 1999 ; ebihara and ejiri , 2003 ] . thus , using a ratio of the species abundance with h - ion data can account for any unintended observational bias . the use of the ratios also removes the effect of the neutral concentration profile , allowing one to better address charge exchange lifetimes . the measurements in figure 4 show that large increases occur in the abundance of he - ion relative to h - ion and o - ion relative to h - ion in the equatorial magnetosphere at the time of all geomagnetic disturbances as indicated by the dst index . we note that h - ions are still the dominant ion species for the events reported herein . the persistence of the increases in he - ion abundance depends strongly on the l value . the persistence is quite limited , on the order of 1 day , at the lower l values ( l3 ) and substantially longer , on the order of 10 days , at the highest l values ( l6 ) . conversely , the persistence of the increases in o - ion abundance is not associated with l value , as the injection decay , lasting on the order of 1 day , is observed across all l shells equally ( figure 4 ( bottom ) ) . this difference in the persistence of the he - ion and o - ion abundances as a function of l value is quantified in figure 5 for a sample period of 2013 day of year 70 to 195 . in this figure , the values of the he / h and o / h ratios are plotted as a function of time , orbit by orbit , averaged over the ratio values in three l bands : l = 34 ( black data points ) , l = 45 ( green ) , and l = 56 ( red ) . through exponential fits to 20 injection events , we report that the average decay rate , as determined by the e - folding time , for he - ions in the l = 34 band to be 0.8 days , for he - ions in the l = 45 band to be 1.1 days , and in the l = 56 band to be 1.7 days . uncertainties on each of these fits are estimated to be 0.2 days and due to constraints on the initial amplitude and baseline value of the he / h ratio . at the times of increase ( times of particle injection ) in the relative he - ion abundance , after the decay of the he - ion population relative to the h - ion in this energy band , the he / h ratios at all l values can fall to less than 1% . ( first and third panels ) he - ion / h - ion and o - ion / h - ion ratios across the entire rbspice instrument energy ranges , respectively , from figure 3 but plotted over 2013 day of year ( doy ) 70196 . ( second and fourth panels ) time traces of the average ( log ) ratio in three l shell bins ; black for l = 34 , green for l = 45 , and red for l = 56 . this l shell dependence in decay is not observed in the relative o - ion abundance and instead exhibits uniform decay across all l shells . furthermore , the decay time is quite rapid , occurring with an e - folding time of 1.5  0.1 h. as indicated in all figures , the h - ion , he - ion , and o - ion abundance and ratio values are correlated with geomagnetic activity , which is consistent with previous observations [ e.g. , kronberg et al . , 2012 ] . the use of the  total abundance  values herein are an effort to ascertain the total flux of the ring current species . these values assist in our understanding ring current populations and of ionospheric outflow densities , which are the primary contributor to o - ions during geomagnetic events [ daglis et al . , 1999 ] . we also note our inherent assumption that the loss rate is inferred based on the persistence time of ions after an injection event . it is possible that , however , there are some continued source of heavier ions ( particularly at high l ) even during the recovery phase generally , the l shell dependence of the he - ion and o - ion plasma decay is likely the result of charge exchange loss processes which , due to the falloff of neutral hydrogen density with altitude , causes a loss of the innermost l shells faster than the outermost regions . the measured he - ion lifetimes reported herein seem to support this approach and correspond to previously published lifetime calculations [ ebihara and ejiri , 2003 ] . however , the rapid o - ion loss rate is not expected based on our current understanding of o - ion charge exchange . we suspected such rapid loss in the o - ions was due to the inclusion of the higher - energy ( i.e. , greater than 500 kev ) o - ions in our o / h ratios . in figure 6 we repeat the same presentation used for figure 5 , but now constrain the ratios such that only the common energy values depicted in figure 1 are used . with the use of such common energy ranges , the observed o / h ratios now match that of ebihara and ejiri . specifically , o / h e - folding decay times were found to be 0.3 days for the l = 34 band , 0.5 days for the l = 45 band , and 0.8 days for the l = 56 band . thus , it is the rapid loss of high - energy o - ion that gives rise to the extremely short lifetimes apparent in figure 5 . to our knowledge this is the first time that such rapid loss rates associated with high - energy o - ions have been observed . the reason for such fast decay for high - energy o - ions is unclear , but could be due to diffusive or convective outflow processes or perhaps field line curvature scattering [ ebihara et al . , in addition , we note that the use of common energy ranges also slightly extended the measured he / h lifetimes due to the exclusion of , otherwise faster decaying , lower energy he - ions . ( first and third panels ) he - ion / h - ion and o - ion / h - ion ratios across the common rbspice instrument energy ranges , respectively , from figure 3 but plotted over 2013 doy 70196 . ( second and fourth panels ) time traces of the average ( log ) ratio in three l shell bins ; black for l = 34 , green for l = 45 , and red for l = 56 . , we note that there are time periods in which other loss processes seem to be occurring . for example , as seen in figures 2 and 4 , the apparent loss of o - ions around day of year 100 , 130 , and 165 at higher l shells , before lower l shells , is intriguing . in addition , from the same figures , it is observed that he - ions enter the inner magnetosphere without simultaneous o - ions around day of year 20 and 70 . such an event could be associated with direct coupling of the solar wind without induced terrestrial outflow . understanding the dynamics of these periods , which perhaps involve wave - particle interaction processes and solar wind conditions , is ongoing and will be explored in future studies . these will incorporate , as required , electric and magnetic field data acquired by van allen probes instruments .
h - ion ( 45 kev to 600 kev ) , he - ion ( 65 kev to 520 kev ) , and o - ion ( 140 kev to 1130 kev ) integral flux measurements , from the radiation belt storm probe ion composition experiment ( rbspice ) instrument aboard the van allan probes spacecraft b , are reported . 
 these abundance data form a cohesive picture of ring current ions during the first 9 months of measurements . furthermore 
 , the data presented herein are used to show injection characteristics via the he - ion / h - ion abundance ratio and the o - ion / h - ion abundance ratio . of unique interest 
 to ring current dynamics are the spatial - temporal decay characteristics of the two injected populations . 
 we observe that he - ions decay more quickly at lower l shells , on the order of 0.8 day at l shells of 34 , and decay more slowly with higher l shell , on the order of 1.7 days at l shells of 56 . 
 conversely , o - ions decay very rapidly ( 1.5 h ) across all l shells . 
 the he - ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange . 
 the o - ion decay time is much faster than predicted and is attributed to the inclusion of higher - energy ( > 500 kev ) o - ions in our decay rate estimation . 
 we note that these measurements demonstrate a compelling need for calculation of high - energy o - ion loss rates , which have not been adequately studied in the literature to date.key pointswe report initial observations of ring current ionswe show that he - ion decay rates are consistent with theorywe show that o - ions with energies greater than 500 kev decay very rapidly