Combined Release And Radiation Effects Satellite Research Articles

A New Approach to Constructing Models of Electron Diffusion by EMIC Waves in the Radiation Belts

AbstractElectromagnetic ion cyclotron (EMIC) waves play an important role in relativistic electron losses in the radiation belts through diffusion via resonant wave‐particle interactions. We present a new approach for calculating bounce and drift‐averaged EMIC electron diffusion coefficients. We calculate bounce‐averaged diffusion coefficients, using quasi‐linear theory, for each individual Combined Release and Radiation Effects Satellite (CRRES) EMIC wave observation using fitted wave properties, the plasma density and the background magnetic field. These calculations are then combined into bounce‐averaged diffusion coefficients. The resulting coefficients therefore capture the combined effects of individual spectra and plasma properties as opposed to previous approaches that use average spectral and plasma properties, resulting in diffusion over a wider range of energies and pitch angles. These calculations, and their role in radiation belt simulations, are then compared against existing diffusion models. The new diffusion coefficients are found to significantly improve the agreement between the calculated decay of relativistic electrons and Van Allen Probes data.

Drift echoes and flux oscillations: A signature of prompt and diffusive changes in the radiation belts

Prompt creation of new multi-MeV electron and proton radiation belts in the normally benign slot region between inner and outer Van Allen zones was observed by the short-lived Combined Release and Radiation Effects Satellite (CRRES) mission almost 30 years ago. Flux oscillations at lower energies coincident with ULF wave measurements and consistent with drift resonance were also a feature of the CRRES observations. The next mission designed to study the radiation belts in similar detail from a near equatorial plane orbit was the Van Allen Probes launched in August 2012. These twin spacecraft in similar orbits observed many milder events which produce drift echoes indicative of injection over a limited range of longitude on less than an electron drift time. Related substorm injection drift echoes were also observed by Van Allen Probes with much higher energy resolution than previously. Along with other flux oscillations associated with Ultra Low Frequency (ULF) waves, these events form a class which contributes to the overall radial transport and energization of radiation belt electrons as well as protons. This paper focuses on the greatly improved measurements from the Van Allen Probes relative to the CRRES era. These measurements illuminate our understanding of the importance of flux oscillations as a signature of radial transport relative to other energization and loss processes affecting the radiation belts.

Magnetic field power spectra and magnetic radial diffusion coefficients using CRRES magnetometer data

AbstractWe used the fluxgate magnetometer data from Combined Release and Radiation Effects Satellite (CRRES) to estimate the power spectral density (PSD) of the compressional component of the geomagnetic field in the ∼1 mHz to ∼8 mHz range. We conclude that magnetic wave power is generally higher in the noon sector for quiet times with no significant difference between the dawn, dusk, and the midnight sectors. However, during high Kp activity, the noon sector is not necessarily dominant anymore. The magnetic PSDs have a very distinct dependence on Kp. In addition, the PSDs appear to have a weak dependence on McIlwain parameter L with power slightly increasing as L increases. The magnetic wave PSDs are used along with the Fei et al. (2006) formulation to compute as a function of L and Kp. The L dependence of is systematically studied and is shown to depend on Kp. More significantly, we conclude that is the dominant term driving radial diffusion, typically exceeding by 1–2 orders of magnitude.

On long decays of electrons in the vicinity of the slot region observed by HEO3

AbstractLong decay periods of electron counts, which follow abrupt rises and last from weeks to months, have been observed by the HEO3 spacecraft in the vicinity of the slot region between the years 1998 and 2007. During the most stable decay periods as selected, e‐folding timescales are extracted and statistically analyzed from observations as a function of L‐shell and electron energy. A challenge is to reproduce the observed timescales from simulations of pitch angle diffusion by three acting waves—the plasmaspheric hiss, lightning‐generated whistlers, and VLF transmitter waves. We perform full numerical simulations to accurately compute electron lifetimes. We choose to use the method and wave parameters proposed by Abel and Thorne in 1998 with the goal to assess whether they can reproduce lifetimes extracted from HEO observations. We show how hiss dominantly affect high energy electrons (E > 2 MeV) for L in [2, 3.5] and VLF transmitter waves control residency times of low energy electrons (<0.4 MeV) around L = 2. These interactions induce characteristic shapes of the lifetime profiles that will be discussed. We show how the wave amplitudes can be adjusted for the particular energy particles that are dominantly affected by one wave type only. Using these amplitudes, mean HEO lifetimes are reproduced within a factor 2 to 5. VLF occurrence rates and hiss amplitude turn out significantly higher than those proposed by Abel and Thorne. The wide energy response of the sensors complicates the analysis because it blurs the electron lifetime dependence on energy, increases the overall lifetimes, and reduces the differences between the different channel lifetimes. In particular, our simulations suggest the flux measured by an integrated energy sensor aboard HEO has a variable slope, i.e., a variable lifetime, during 10–20 days in our data, due to the faster decay of the low residency time particles while slower decaying particles control the steady decay. It can explain some of the multi‐slopes decays observed by HEO. HEO electron long decay timescales are also compared to the timescales previously observed from Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) and Combined Release and Radiation Effects Satellite (CRRES) with differences attributed to factors such as instrument characteristic and different satellite orbits.

Global morphology and spectral properties of EMIC waves derived from CRRES observations

AbstractGyroresonant wave‐particle interactions with electromagnetic ion cyclotron (EMIC) waves are a potentially important loss process for relativistic electrons in the Earth's radiation belts. Here we perform a statistical analysis of the EMIC waves observed by the Combined Release and Radiation Effects Satellite (CRRES) to determine the global morphology and spectral properties of the waves and to help assess their role in radiation belt dynamics. Helium band EMIC waves, with intensities, , greater than 0.1 nT2, are most prevalent during active conditions (AE> 300 nT), from 4 <L*< 7 in the afternoon sector, with an average percentage occurrence of 2.7%. Hydrogen band EMIC wave events, with intensities greater than 0.1 nT2, are also most prevalent in the afternoon sector during active conditions in the same region, but they are less frequent with an average percentage occurrence of 0.6%. The average intensity of the helium and hydrogen band EMIC waves in the region 4 <L*< 7 in the afternoon sector during active conditions is 2 nT2 and 0.5 nT2, respectively, and suggests that the waves can cause strong diffusion. However, the time‐averaged properties are very different, being a factor of 30–50 lower for helium and hydrogen band EMIC waves, respectively, suggesting that the overall effect will be correspondingly weaker. Nevertheless, the moderate and strong EMIC wave events with reported on here will contribute to relativistic electron loss in the Earth's radiation belts and should be included in radiation belt models.

Modeling radiation belt electron dynamics during GEM challenge intervals with the DREAM3D diffusion model

AbstractAs a response to the Geospace Environment Modeling (GEM) “Global Radiation Belt Modeling Challenge,” a 3D diffusion model is used to simulate the radiation belt electron dynamics during two intervals of the Combined Release and Radiation Effects Satellite (CRRES) mission, 15 August to 15 October 1990 and 1 February to 31 July 1991. The 3D diffusion model, developed as part of the Dynamic Radiation Environment Assimilation Model (DREAM) project, includes radial, pitch angle, and momentum diffusion and mixed pitch angle‐momentum diffusion, which are driven by dynamic wave databases from the statistical CRRES wave data, including plasmaspheric hiss, lower‐band, and upper‐band chorus. By comparing the DREAM3D model outputs to the CRRES electron phase space density (PSD) data, we find that, with a data‐driven boundary condition at Lmax = 5.5, the electron enhancements can generally be explained by radial diffusion, though additional local heating from chorus waves is required. Because the PSD reductions are included in the boundary condition at Lmax = 5.5, our model captures the fast electron dropouts over a large L range, producing better model performance compared to previous published results. Plasmaspheric hiss produces electron losses inside the plasmasphere, but the model still sometimes overestimates the PSD there. Test simulations using reduced radial diffusion coefficients or increased pitch angle diffusion coefficients inside the plasmasphere suggest that better wave models and more realistic radial diffusion coefficients, both inside and outside the plasmasphere, are needed to improve the model performance. Statistically, the results show that, with the data‐driven outer boundary condition, including radial diffusion and plasmaspheric hiss is sufficient to model the electrons during geomagnetically quiet times, but to best capture the radiation belt variations during active times, pitch angle and momentum diffusion from chorus waves are required.

Chorus functional dependencies derived from CRRES data

Using data from the Combined Release and Radiation Effects Satellite (CRRES) plasma wave experiment, we present quadratic fits to the mean of the wave amplitude squared, , for lower and upper band chorus as a function of geomagnetic activity (Kp) and magnetic latitude (λ) for the midnight (21<MLT≤3), dawn (3<MLT≤9), and postnoon (12<MLT≤15) sectors and present an ad hoc model for the prenoon (9<MLT≤12) sector. The empirical models are valid for 4≤L≤7, |λ|<15° and Kp≤6 and quantify the dramatic difference in the latitudinal dependence of chorus as a function of local time and how that dependence varies with geomagnetic condition, critical parameters for calculating wave‐induced electron scattering rates. Our results are generally consistent with previous studies, and our key contribution is the quantification of wave properties in a manner that is easily incorporated into global quasi‐linear diffusion models.

Long-term relativistic radiation belt electron responses to GEM magnetic storms

We present a long-term radiation belt simulation for a 200-day period starting on 25 January 1991, which includes both six geomagnetic storms identified by the Geospace Environment Modeling (GEM) focus group and non-stormy periods of the Combined Release and Radiation Effects Satellite (CRRES) mission, using 3-D time-dependent Versatile Electron Radiation Belt (VERB) code, and compare the simulation results with a multisatellite phase space density (PSD) reanalysis obtained using Kalman filtering of observations from CRRES, GEO, GPS, and Akebono satellites, as well as with the CRRES MEA 1MeV electron observation. The processes accounted for in the model are radial diffusion-driven by ultra-low frequency (ULF) electromagnetic fluctuations and local (pitch-angle and energy) scattering by plasmaspheric hiss and chorus waves, respectively, inside and outside the plasmasphere. The observations show that a significant decrease in the relativistic electrons in the outer radiation belt is observed in association with the solar wind dynamic pressure enhancement during the main phase of each storm, while during the recovery phase, different types of relativistic electron flux profiles are identified: increased, decreased, and unchanged relative to the pre-storm flux level. First, for an increase of relativistic electrons relative to the pre-storm flux level, the comparison of simulation with reanalysis shows that inward radial diffusion and local acceleration coupled with each other result in a net acceleration. Second, for a decrease or lack of change in relativistic electrons, competing effects of pitch-angle scattering, outward diffusion, and acceleration produce the net decrease in electron PSD and fluxes. The results show that the overall time evolution of the radiation belt is in good agreement with our model simulations, indicating that modeling, including radial diffusion and pitch-angle scattering, is reasonable in predicting the general long-term structure of the outer radiation belt. In addition, with the assistance of local acceleration by chorus waves, the overall flux level in the outer radiation belt becomes comparable to the observation.

Relativistic radiation belt electron responses to GEM magnetic storms: Comparison of CRRES observations with 3‐D VERB simulations

Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in‐depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time‐dependent 3‐D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch angle scattering by plasmaspheric hiss inside the plasmasphere. The 3‐D VERB simulations show that during the storm main phase and early recovery phase the estimated plasmapause is located deep in the inner region, indicating that pitch angle scattering by chorus waves can be a dominant loss process in the outer belt. We have also confirmed the important role played by mixed energy‐pitch angle diffusion by chorus waves, which tends to reduce the fluxes enhanced by local acceleration, resulting in comparable levels of computed and measured fluxes. However, we cannot reproduce the more pronounced flux dropout near the boundary of our simulations during the main phase, which indicates that non‐adiabatic losses may extend toL‐shells lower than our simulation boundary. We also provide a detailed description of simulations for each of the GEM storm events.

Long-term radiation belt simulation with the VERB 3-D code: Comparison with CRRES observations

[1] Highly energetic electrons in the Earth’s radiation belts are hazardous for satellite equipment. Fluxes of relativistic electrons can vary by orders of magnitude during geomagnetic storms. The evolution of relativistic electron fluxes in the radiation belts is described by the 3-D Fokker-Planck equation in terms of the radial distance, energy, and equatorial pitch angle. To better understand the mechanisms that control radiation belt acceleration and loss and particle flux dynamics, we present a long-term radiation belt simulation for 100 days from 29 July to 6 November 1990 with the 3-D Versatile Electron Radiation Belt (VERB) code and compare the results with the electron fluxes observed by the Combined Release and Radiation Effects Satellite (CRRES). We also perform a comparison of Phase Space Density with a multisatellite reanalysis obtained by using Kalman filtering of observations from CRRES, Geosynchronous (GEO), GPS, and Akebono satellites. VERB 3-D simulations include radial, energy, and pitch angle diffusion and mixed energy and pitch angle diffusion driven by electromagnetic waves inside the magnetosphere with losses to the atmosphere. Boundary conditions account for the convective source of electrons and loss to the magnetopause. The results of the simulation that include all of the above processes show a good agreement with the data. The agreement implies that these processes are important for the radiation belt electron dynamics and therefore should be accounted for in outer radiation belt simulations. We also show that the results are very sensitive to the assumed wave model. Our simulations are driven only by the variation of the Kp index and variations of the seed electron population around geosynchronous orbit, which allows the model to be used for forecasting and nowcasting.

Oxygen torus in the deep inner magnetosphere and its contribution to recurrent process of O+-rich ring current formation

[1] Using the magnetic field and plasma wave data obtained by the Combined Release and Radiation Effects Satellite (CRRES), we search for enhancements of O+ ion density in the deep inner magnetosphere known as “the oxygen torus”. We examine 4 events on the dayside in which toroidal standing Alfven waves appear clearly. From the frequency of the toroidal waves, the magnetospheric local mass density (ρL) is estimated by solving the MHD wave equation for realistic models of the magnetic field and the field line mass distribution. We also estimate the local electron number density (neL) from the plasma wave spectrograms by identifying narrow-band emission at the upper-hybrid resonance frequency. Assuming the quasi-neutral condition of plasma, we infer the local average ion mass (ML) by ρL/neL. It is found that ML is approximately 3 amu in the plasma trough, while it shows an enhancement of >7 amu at L ∼ 4.5–6.5 that is close to the plasmapause at L ∼ 3.5–6.0. This indicates an existence of the oxygen torus in the vicinity of the plasmapause. The oxygen torus is found preferentially during the storm recovery phase. We interpret that these features of the oxygen torus (i.e., close relations with the plasmapause and the storm recovery phase) reflect its generation mechanism; that is, the ionospheric temperature is enhanced by heat conduction from high altitudes in the limited L range where the plasmasphere, because of its inflation during the recovery phase, encounters the ring current, and then the ionosphere has a larger scale height and supplies O+ ions to the inner magnetosphere, resulting in the oxygen torus. We also discuss the contribution of the oxygen torus to the formation of the O+-rich ring current. It is proposed that the O+-rich ring current is formed in a recurrent process, in which the oxygen torus, the plasmasphere, and the ring current interact with each other.

Solar cycle dependence of bulk ion composition at geosynchronous orbit

[1] While the average ion mass M (normalized to amu) of bulk plasma at geosynchronous orbit has been calculated at solar maximum (during the era of the Combined Release and Radiation Effects Satellite (CRRES)), the solar cycle dependence of bulk ion composition at geosynchronous orbit is not known. Here, we use measurements of mass density ρm from Alfven wave frequencies measured by the Geostationary Operational Environmental Satellites and ion density measurements by the Magnetospheric Particle Analyzer (MPA) on Los Alamos National Laboratory (LANL) spacecraft to establish the solar cycle dependence of bulk ion composition. We show that there is a strong correlation between the yearly median value of ρm, ρm,yr−med, and the yearly average of the solar EUV flux F10.7, F10.7,yr−av; log10(ρm,yr−med) ≃ 0.5089 + 0.003607F10.7,yr−av (for ρm values adjusted to a magnetic latitude MLAT of 8°). We calibrate the measurements of the MPA instrument on one spacecraft to those from another by using yearly median density values. Then, using close conjunctions of LANL spacecraft with CRRES (for which we have inferred values of ρm and ne), we calibrate the ideal theoretical value of MPA ion density nMPA−th (the value that MPA would measure if it measured all the ions) to the observed values directly measured by the instrument, nMPA−obs. We find that nMPA−th is approximately 1.47 times the value of nMPA−obs measured by the LANL 1994 spacecraft. Using the yearly median values of ρm as a function of F10.7, the yearly median values of nMPA−th from the MPA instruments, and a model for the concentration of He+, we are able to calculate the solar cycle dependence of the average ion mass M and the O+ concentration ηO+ ≡ nO+/ne. We find that M is typically ∼3.8 at solar maximum and near unity at solar minimum. Typical values of ηO+ vary by 2 orders of magnitude over the solar cycle, from about 0.2 at solar maximum to ∼2 × 10−3 at solar minimum. Furthermore, our results also demonstrate that the typical concentration of He+ must also be very low at solar minimum. Since the median yearly values of density are low, characteristic of the plasma trough, our results are most applicable to that region. Considering, however, that the plasmasphere and plume typically have a low concentration of O+, the concentration of O+ at geosynchronous orbit at solar minimum is likely to be low for all conditions (with the possible exception of very low densities for which the high-energy component might dominate).

Statistical analysis of pitch angle distribution of radiation belt energetic electrons near the geostationary orbit: CRRES observations

[1] A statistical analysis of energetic radiation belt electron pitch angle distributions (PADs) at the radial distances of 6 RE and 6.6 RE is performed on the basis of the pitch angle resolved flux observations from the Medium Electrons A (MEA) instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). While previous studies of Vampola (1998) and Gannon et al. (2007) have used CRRES MEA data to investigate the general variations in electron PAD at particular energies, in this study we present a detailed statistical analysis of electron PADs including the dependence on electron kinetic energy, magnetic local time (MLT), and the level of geomagnetic activity. By fitting the measured PADs with a power law function of sine of local pitch angle, the power law index n that relates to the category of radiation belt electron PAD is quantified in detail as a function of electron kinetic energy, MLT interval, and geomagnetic index Kp. Statistical averaged n values vary considerably with respect to MLT, ranging from n ∼ 0 within 0000–0400 MLT to n ∼ 1.5 within 1200–1600 MLT, because of the MLT dependence of wave scattering and the effects associated with drift shell splitting and magnetopause shadowing. Drift shell splitting and magnetopause shadowing result in often observed negative values of n. At lower energies of a few hundred keV the pitch angle distributions are more flat than at MeV energies, which is consistent with faster pitch angle scattering at low energies by chorus waves. These quantitative results of radiation belt electron PAD, consistent with the previous studies by Vampola (1998) and Gannon et al. (2007), provide further insight into the global dynamics of energetic radiation belt electrons near the geostationary orbit and also are useful for inferring electron phase space densities and assimilating their radial profiles using omnidirectional electron flux measurements.

The Trapped Proton Environment in Medium Earth Orbit (MEO)

Energetic proton flux maps of the differential flux intensity in the medium-Earth orbit (MEO) regime (altitudes ~ 7000-15,000 km) are developed from measurements taken by detectors aboard the Combined Release and Radiation Effects Satellite (CRRES), HEO-F1, HEO-F3 and ICO satellites. Measurement errors have been estimated by cross-calibrating to a standard sensor aboard the GOES satellite during solar proton events. Spectral inversion techniques were employed to derive differential flux spectra from the HEO and ICO integral channel dosimeters. Two methods for combining the four different satellite data sets on a standard energy and coordinate grid are presented and the ramifications due to limited spatial and temporal coverage are explored. Comparison to the NASA AP-8 models shows the new model median flux maps to be of approximately equivalent or lower magnitude in the slot region while new model 95th percentile maps are always higher. Implications for the proton dose received by MEO satellites are discussed.

Pc5 wave power in the quiet‐time plasmasphere and trough: CRRES observations

The Combined Release and Radiation Effects Satellite (CRRES) mission provides an opportunity to study the distribution of MHD wave power in the inner magnetosphere both inside the high‐density plasmasphere and in the low‐density trough. We present a statistical survey of Pc5 power using CRRES magnetic field, electric field, and plasma wave data separated into plasmasphere and trough intervals. Using a database of plasmapause crossings, we examined differences in power spectral density between the plasmasphere and trough regions. These differences were typically a factor of 3 or 4 but could be as much as an order of magnitude and could be seen in both electric and magnetic field data. Our study shows that determining the plasmapause location is important for understanding and modeling the MHD wave environment in the Pc5 frequency band.

Origin of energetic electron precipitation >30 keV into the atmosphere

Energetic electrons are deposited into the atmosphere from Earth's inner magnetosphere, resulting in the production of odd nitrogen (NOx). During polar night, NOx can be transported to low altitudes, where it can destroy ozone, affecting the atmospheric radiation balance. Since the flux of energetic electrons trapped in the magnetosphere is related to solar activity, the precipitation of these electrons into Earth's atmosphere provides a link between solar variability and changes in atmospheric chemistry which may affect Earth's climate. To determine the global distribution of the precipitating flux, we have built a statistical model binned by auroral electrojet (AE) index, magnetic local time (MLT), and L shell of E > 30 keV precipitating electrons from the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA Polar Orbiting Environmental Satellites (POES) low‐altitude satellites NOAA‐15, NOAA‐16, NOAA‐17, and NOAA‐18. We show that the precipitating flux increases with geomagnetic activity, suggesting that the flux is related to substorm activity. The precipitating fluxes maximize during active conditions where they are primarily seen outside of the plasmapause on the dawnside. The global distribution of the precipitating flux of E > 30 keV electrons is well‐correlated with the global distribution of lower‐band chorus waves as observed by the plasma wave experiment onboard the Combined Release and Radiation Effects Satellite (CRRES) satellite. In addition, the electron precipitation occurs where the pitch angle diffusion coefficient due to resonant interaction between electrons and whistler mode chorus waves is high, as calculated using the pitch angle and energy diffusion of ions and electrons (PADIE) code. Our results suggest that lower‐band chorus is very important for scattering >30 keV electrons from Earth's inner magnetosphere into the atmosphere.

Coupling Processes in the Inner Magnetosphere: Inner Magnetosphere Coupling (IMC) Workshop; Espoo, Finland, 28 July to 1 August 2008

In recent years, satellite measurements (e.g., Combined Release and Radiation Effects Satellite (CRRES); Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE); Polar; Highly Elliptical Orbit (HEO); Cluster; Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX); and Time History of Events and Macroscale Interactions During Substorms (THEMIS)) and theoretical and modeling studies have significantly advanced the understanding of the dynamics of various plasma populations in the inner magnetosphere. Observations and modeling have revealed that the dynamics of the inner magnetospheric plasma populations not only depend on solar wind conditions but also are coupled to each other bymeans of the electromagnetic field, currents, and wave‐particle interactions.The understanding of coupling processes between the plasmasphere, ring current, radiation belts, magnetic field, and waves was the subject of discussion at the recent Inner Magnetospheric Coupling (IMC) workshop, which brought together more than 50 researchers studying various plasma populations and processes that may influence the inner magnetosphere, as well as the effects of the inner magnetosphere on the ionosphere, atmosphere, and global magnetospheric interactions.

Ion composition in the plasma trough and plasma plume derived from a Combined Release and Radiation Effects Satellite magnetoseismic study

The mass and energy carried in the magnetosphere by heavy ions, O+ in particular, are known to increase as geomagnetic activity increases. However, the ion composition in the magnetosphere has not been fully specified since measurements of the flux of different ion species from the ionospheric thermal energy (below 1 eV) to the ring current energy (above 100 keV) are difficult with single‐particle instruments. We used mass density determined by a magnetoseismology technique and the electron density derived from measured plasma wave spectra to investigate the ion composition and total mass density for Combined Release and Radiation Effects Satellite (CRRES) orbit 962 (27−28 August 1991). This orbit occurred during a geomagnetic storm and included afternoon passes through the plasmasphere, the plasma trough, and a plasma plume, where these plasma regions were identified using the electron density ne. In the magnetoseismology analysis, we determined the fundamental frequency of the toroidal standing Alfvén waves fT1 from the electric and magnetic field data and then inferred the corresponding total mass density ρtotal at the satellite by solving an MHD wave equation with a realistic magnetic field model and a realistic assumption for the mass distribution along the field line. The value of fT1 changed little when the spacecraft moved between the plasma trough and the plasma plume, implying the dominance of heavy ions in the plasma trough. From the values of ne and ρtotal, we derived quantities associated with O+ by assuming that the plasma consisted of three ions, H+, He+, and O+. In the plasma trough, O+ ions are found to carry a number density of ∼10 cm−3, ∼50% of the number density, and ∼90% of the mass density. On the other hand, O+ is found to be much less dominant in the plasma plume. Our results are consistent with DE‐1 studies of the formation of an oxygen torus at the outer edge of the H+ plasmapause during geomagnetic active periods and with GEOS‐1 and GEOS‐2 studies that reported strong dependence of O+ density on geomagnetic activity and on solar extreme ultraviolet flux. In addition, our events indicate that the plasma plume boundary, defined in terms of the number density of electrons or light ions (H+ and He+), may not exhibit similar structure in the total mass density that can be readily detected using magnetoseismology techniques.

Survey of magnetosonic waves and proton ring distributions in the Earth's inner magnetosphere

Fast magnetosonic waves can lead to the local acceleration of electrons from ∼10 keV up to a few MeV on a timescale of 1–2 d and may play an important role in radiation belt dynamics. Here we present a survey of wave and particle data from the Combined Release and Radiation Effects Satellite (CRRES) to determine the global morphology of the waves as a function of magnetic activity, and to investigate the role of proton rings as a potential source mechanism. The intensity of fast magnetosonic waves in the frequency range 0.5 fLHR < f < fLHR increases with increasing magnetic activity suggesting they are related to periods of enhanced convection and/or substorm activity. They are observed at most magnetic local times (MLT) outside the plasmapause but are restricted to the dusk sector inside the plasmapause. The MLT distribution of low energy proton rings (ER < 30 keV) with energies exceeding the Alfvén energy (ER > EA) required for instability closely matches the distribution of magnetosonic waves on the dusk side, both inside and outside the plasmapause, suggesting that low energy proton rings are a likely source of energy driving the waves. However, intense magnetosonic waves are also observed outside the plasmapause on the dawn‐side that do not satisfy (ER > EA). Although proton rings with ER > 30 keV could drive the instabilities, the source of these waves is yet to be properly identified. Since fast magnetosonic waves can accelerate electrons we suggest that they may provide a significant energy transfer process between the ring current and the outer electron radiation belt.

Electron scattering by whistler‐mode ELF hiss in plasmaspheric plumes

Nonadiabatic loss processes of radiation belt energetic electrons include precipitation loss to the atmosphere due to pitch‐angle scattering by various magnetospheric plasma wave modes. Here we consider electron precipitation loss due to pitch‐angle scattering by whistler‐mode ELF hiss in plasmaspheric plumes. Using wave observations and inferred plasma densities from the Plasma Wave Experiment on the Combined Release and Radiation Effects Satellite (CRRES), we analyze plume intervals for which well‐determined hiss spectral intensities are available. We then select 14 representative plumes for detailed study, comprising 10 duskside plumes and 4 nonduskside plumes, with local hiss amplitudes ranging from maximum values of above 300 pT to minimum values of less than 1 pT. We estimate the electron loss timescale τloss due to pitch‐angle scattering by hiss in each chosen plume as a function of L‐shell and electron energy; τloss is calculated from quasi‐linear theory as the inverse of the bounce‐averaged diffusion rate evaluated at the equatorial loss cone angle. We find that pitch‐angle scattering by hiss in plumes can be efficient for inducing precipitation loss of outer‐zone electrons with energies throughout the range 100 keV to 1 MeV, though the magnitude of τloss can be highly dependent on wave power, L‐shell, and electron energy. For 100‐ to 200‐keV electrons, typically τloss ∼ 1 day while the minimum loss timescale (τloss)min ∼ hours. For 500‐keV to 1‐MeV electrons, typically (τloss)min ∼ days, while (τloss)min < 1 day in the case of large wave amplitude (∼100's pT). Apart from inducing direct precipitation loss of MeV electrons, scattering by hiss in plumes may reduce the generation of MeV electrons by depleting the lower energy electron seed population. Models of the dynamical variation of the outer‐zone electron flux should incorporate electron precipitation loss induced by ELF hiss scattering in plasmaspheric plumes.