Combined Release And Radiation Effects Satellite Research Articles

Storm-Time Evolution of Energetic Electron Pitch Angle Distributions by Wave-Particle Interaction

The quasi-pure pitch-angle scattering of energetic electrons driven by field-aligned propagating whistler mode waves during the 9∼15 October 1990 magnetic storm at L ≈ 3 ∼ 4 is studied, and numerical calculations for energetic electrons in gyroresonance with a band of frequency of whistler mode waves distributed over a standard Gaussian spectrum is performed. It is found that the whistler mode waves can efficiently drive energetic electrons from the larger pitch-angles into the loss cone, and lead to a flat-top distribution during the main phase of geomagnetic storms. This result perhaps presents a feasible interpretation for observation of time evolution of the quasi-isotropic pitch-angle distribution by Combined Release and Radiation Effects Satellite (CRRES) spacecraft at L ≈ 3 ∼ 4.

A Kalman filter technique to estimate relativistic electron lifetimes in the outer radiation belt

Data assimilation aims to smoothly blend incomplete and inaccurate observational data with dynamical information from a physical model, and has become an increasingly important tool in understanding and predicting meteorological, oceanographic and climate processes. As space‐borne observations become more plentiful and space‐physics models more sophisticated, dynamical processes in the radiation belts can be analyzed using advanced data assimilation methods. We use the Extended Kalman filter and observations from the Combined Release and Radiation Effects Satellite (CRRES) to estimate the lifetime of relativistic electrons during magnetic storms in the Earth's outer radiation belt. The model is a linear parabolic partial differential equation governing the phase‐space density. This equation contains empirical coefficients that are not well‐known and that we wish to estimate, along with the phase‐space density itself. The assimilation method is first verified on model‐simulated data, which allows us to reliably estimate the characteristic lifetime of the electrons. We then apply the methodology to CRRES measurements and show it to be useful in highlighting systematic differences between the parameter estimates for storms driven by coronal mass ejections (CMEs) and by corotating interaction regions (CIRs), respectively. These differences are attributed to the complex, competing effects of acceleration and loss processes during distinct physical regimes. The technique described herein may be applied next to constrain more sophisticated radiation belt and ring current models, as well as in other areas of magnetospheric physics.

Correction to “Effect of oblique electromagnetic ion cyclotron waves on relativistic electron scattering: Combined Release and Radiation Effects Satellite (CRRES)-based calculation”

[1] We consider the effect of oblique electromagnetic ion cyclotron (EMIC) waves on relativistic electron scattering in the outer radiation belt (RB) using simultaneous observations of plasma and wave parameters from Combined Release and Radiation Effects Satellite (CRRES). The main findings can be summarized as follows. First, in comparison with field-aligned waves, intermediate and highly oblique distributions decrease the range of pitch angles subject to diffusion and reduce the local scattering rate by about an order of magnitude at pitch angles where the principle n = 1 resonances operate. Oblique waves allow the n > 1 resonances to operate, extending the range of local pitch angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude. Second, the local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Consequently, it is likely that the bounce-averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations. Third, in comparison with field-aligned waves, intermediate and highly oblique waves decrease the bounce-averaged scattering rate near the edge of the equatorial loss cone by orders of magnitude if the electron energy does not exceed a threshold (∼2–5 MeV) depending on specified plasma and/or wave parameters. Lastly, for greater electron energies, oblique waves operating the n > 1 resonances are more effective and provide the same bounce-averaged diffusion rate near the loss cone as field-aligned waves do.

Effect of oblique electromagnetic ion cyclotron waves on relativistic electron scattering: Combined Release and Radiation Effects Satellite (CRRES)‐based calculation

We consider the effect of oblique electromagnetic ion cyclotron (EMIC) waves on relativistic electron scattering in the outer radiation belt (RB) using simultaneous observations of plasma and wave parameters from Combined Release and Radiation Effects Satellite (CRRES). The main findings can be summarized as follows. First, in comparison with field‐aligned waves, intermediate and highly oblique distributions decrease the range of pitch angles subject to diffusion and reduce the local scattering rate by about an order of magnitude at pitch angles where the principle n = 1 resonances operate. Oblique waves allow the n > 1 resonances to operate, extending the range of local pitch angle diffusion down to the loss cone, and increasing the diffusion at lower pitch angles by orders of magnitude. Second, the local diffusion coefficients derived from CRRES data are qualitatively similar to the local results obtained for prescribed plasma/wave parameters. Consequently, it is likely that the bounce‐averaged diffusion coefficients, if estimated from concurrent data, will exhibit the dependencies similar to those we found for model calculations. Third, in comparison with field‐aligned waves, intermediate and highly oblique waves decrease the bounce‐averaged scattering rate near the edge of the equatorial loss cone by orders of magnitude if the electron energy does not exceed a threshold (∼2–5 MeV) depending on specified plasma and/or wave parameters. Lastly, for greater electron energies, oblique waves operating the n > 1 resonances are more effective and provide the same bounce‐averaged diffusion rate near the loss cone as field‐aligned waves do.

Pitch angle distribution analysis of radiation belt electrons based on Combined Release and Radiation Effects Satellite Medium Electrons A data

Using data from the Medium Electrons A instrument on the Combined Release and Radiation Effects Satellite (CRRES), a survey of pitch angle distributions (PADs) of energetic electrons is performed. The distributions are classified into three categories: 90°‐peaked, flattop, and butterfly. The categorizations are examined as a function of L‐shell and orbit number and at electron energies of 153, 510, and 976 keV. The 90°‐peaked distributions dominate at the lowest energy channel, and butterfly distributions are more prevalent at higher L values. The PADs on the dayside are predominately 90°‐peaked distributions, while butterfly distributions become more common on the nightside at higher L‐shells. Fitting the PADs to a sinnα form, where α is the local pitch angle, a profile of the parameter n versus L‐shell is produced for local times corresponding to postnoon and midnight sectors for the 510‐keV channel. We then compare the 510‐keV data during times of moderate disturbance to the less disturbed case and the average case, and show an increase in butterfly distributions, which occurs at L > 6 for the nightside case and 3.5 < L < 5.5 for the dayside case. Comparing the profiles for n > 1 before and after the great storm on 24 March 1991, we find that there are significant differences before and after this event, the latter orbits being during a time of higher observed geomagnetic activity. Considering only those PADs with a calculated n > 1, the variation of the 90°‐peaked distributions versus L‐shell and orbit shows increased steepness at lower L‐shell. For the lowest energy channel, the low L‐shell variation of the steepness of the distributions visually correlates with the average 2‐day minimum plasmapause location calculated from a model based on the Dst index over the same time period. For the 510‐keV electrons, a correlation can be seen with the development of flattop distributions inside of the calculated minimum plasmapause location.

Experimentally Derived Resistivity for Dielectric Samples From the CRRES Internal Discharge Monitor

Resistivity values were experimentally determined using charge-storage methods for six samples remaining from the construction of the internal discharge monitor flown on the Combined Release and Radiation Effects Satellite (CRRES). Three tests were performed over a period of three to five weeks each in a vacuum of ~5times10-6 torr with an average temperature of ~25degC to simulate a space environment. Samples tested included FR4, polytetrafluoroethylene (PTFE), and alumina with copper electrodes attached to one or more of the sample surfaces. FR4 circuit-board material was found to have a dark-current resistivity of ~1times1018 Omegamiddotcm and a moderately high polarization current. Fiber-filled PTFE exhibited little polarization current and a dark-current resistivity of ~3times1020 Omegamiddotcm. Alumina had a measured dark-current resistivity of ~3middot1017 Omegamiddotcm, with a very large and more rapid polarization. Experimentally determined resistivity values were two to three orders of magnitude more than found using standard American Society for Testing and Materials (ASTM) test methods. The 1-min wait time suggested for the standard ASTM tests is much shorter than the measured polarization current-decay times for each sample indicating that the primary currents used to determine ASTM resistivity are caused by the polarization of molecules in the applied electric field rather than charge transport through the bulk of the dielectric. Testing over much longer periods of time in vacuum is required to allow this polarization current to decay away and to allow the observation of charged-particle transport through a dielectric material. Application of a simple physics-based model allows separation of the polarization current and dark-current components from long-duration measurements of resistivity over day- to month-long time scales. Model parameters are directly related to the magnitude of charge transfer and storage and the rate of charge transport

Mass density inferred from toroidal wave frequencies and its comparison to electron density

We have estimated the magnetospheric local mass density using the frequency of the toroidal standing Alfvén waves detected with the magnetic (B) and electric (E) field experiments on the Combined Release and Radiation Effects Satellite (CRRES), which had a low‐latitude elliptical orbit (6.3 RE apogee and 18° inclination). A 73‐day period in 1991, which included several geomagnetic storms, was chosen for analysis because the spacecraft was located on the afternoon sector where toroidal waves are routinely excited. Dynamic spectra of the B and E fields were generated for each CRRES orbit for visual identification of toroidal mode ULF waves excited at a number of harmonics. The fundamental mode is the most persistent feature in the spectra, and this mode appears more clearly in the electric field than in the magnetic field. For statistical analysis we determined the fundamental frequency f1 from a separate set of electric field spectra that were computed in a moving 20‐min time window with 10‐min overlap. The frequency is in the range of 1.7–14.2 mHz. The local mass density consistent with f1 was obtained by numerically solving a magnetohydrodynamic wave equation that incorporated the Tsyganenko magnetic field model and an analytical form of field‐line mass density variation that was derived from a recent study of toroidal harmonics. We combined the estimated mass density with the local electron number density ne derived from the plasma wave spectra at CRRES to obtain the local average ion mass M (=ρ/ne). A total of 1094 M samples were obtained, with the majority (95%) coming from the plasmatrough region (ne < 100 cm−3). Our technique for the mass density is confirmed to be reliable because only 3.5% of the M samples lie outside the physically plausible range of 1 amu (all‐H+ plasma) to 16 amu (all‐O+ plasma). The average ion mass has a median value of 3.0 amu and depends on geomagnetic activity. For example, M is 2.5 amu for Dst = 0 and 4.1 amu for Dst = −60 nT. There is a similar dependence of M on Kp, but only when the Kp values are averaged over a few days. There is no strong dependence of M on the magnetic field L shell in the range L = 4 to L = 8 covered by the f1 samples, although M is significantly low (<2 amu) for the plasmaspheric regime (ne > 100 cm−3).

Ion precipitation in the dawn sector during geomagnetic storms

Three southward turnings of the IMF during the magnetic storm of 29–31 October 2003 led to ring current intensifications characterized by Dst minima. Defense Meteorological Satellite Program (DMSP) satellites detected low‐energy ions precipitating equatorward of auroral electrons in the dawn/morning local time sector. These ion fluxes weakened and/or vanished subsequent to Dst recoveries. A survey of the DMSP database reveals that near‐dawn ion precipitation is a main‐phase characteristic of all large magnetic storms. DMSP and Combined Release and Radiation Effects Satellite (CRRES) satellites also detected similar ion precipitation during the main phase of the March 1991 magnetic storm. To reconcile these observations with elementary concepts of ion drifts, the data suggest two source populations. The lowest‐energy ions were initially energized earthward of the plasma sheet electron boundary in the evening sector then corotated eastward. Higher‐energy ions originated in the plasma sheet and drifted close to the Earth under the combined influences of time‐varying convective electric fields and azimuthal gradients in the Earth's magnetic field. We developed a modified Volland Stern model to study test‐particle trajectories in asymmetric magnetic fields and variable electric fields compatible with CRRES measurements. Ions with magnetic moments μ ≥ μc ≈ 14 eV/nT drift duskward. Ions with μ < μc are injected to low L shells during a spike in the convective electric field. As the electric field diminishes and shielding increases, these ions drift toward dawn much closer to Earth than any test electron trajectories. Precipitation in the dawn sector results from a combination of pitch‐angle scattering by intense ambient waves and the dictates of ion drift paths.

Propagation of electromagnetic ion cyclotron wave energy in the magnetosphere

Recent satellite and conjugate observations of Pc 1 electromagnetic ion cyclotron (EMIC) waves have cast doubt on the validity of the long‐standing bouncing wave packet (BWP) model that describes their propagation in the magnetosphere. A study was undertaken using the Combined Release and Radiation Effects Satellite (CRRES) E and B field data to further the understanding of the propagation characteristics of Pc 1 EMIC waves in the middle magnetosphere. CRRES covered the region L = 3.5–8.0, magnetic latitude up to ±30°, and magnetic local time 1400–0800. From 6464 hours of observation a total of 248 EMIC wave events were identified. For the first time the Poynting vector for Pc 1 EMIC waves is presented in the dynamic spectral domain permitting the study of energy propagation of simultaneous waves located in different frequency bands. The maximum wave energy flux for the events was 25 μW/m2, averaging range 1.3 μW/m2, with the direction of wave energy propagation independent of wave frequency but dependent on magnetic latitude. EMIC wave energy propagation was bidirectional both away and toward the equator, for events observed below 11° ∣MLat∣. Unidirectional wave energy propagation away from the equator was observed for all events located above 11° ∣MLat∣. This supports the concept of unidirectional EMIC wave energy propagation away from a broad source region centered on the geomagnetic equator. No measurable energy was observed propagating equatorward beyond the source region, in contradiction to the BWP paradigm.

Stormtime coupling of the ring current, plasmasphere, and topside ionosphere: Electromagnetic and plasma disturbances

We compare plasma and field disturbances observed in the ring current/plasmasphere overlap region and in the conjugate ionosphere during the magnetic storm of 5 June 1991. Data come from the Combined Release and Radiation Effects Satellite (CRRES) flying in a geostationary transfer orbit and three satellites of the Defense Meteorological Satellite Program (DMSP) series in Sun‐synchronous polar orbits. In the region between ring current nose structures and the electron plasma sheet, CRRES detected wave‐like features in local electric and magnetic fields, embedded in structured cold plasmas. Mapped to the ionosphere, these fields should reflect structuring within subauroral plasma streams (SAPS). Indeed, during the period of interest, DMSP F8, F9, and F10 satellites observed highly structured SAPS in the evening ionosphere at topside altitudes. They were collocated with precipitating ring current ions, enhanced fluxes of suprathermal electrons and ions, elevated electron temperatures, and irregular plasma density troughs. Overall, these events are similar to electromagnetic structures observed by DMSP satellites within SAPS during recent geomagnetic storms (Mishin et al., 2003, 2004). Their features can be explained in terms of Alfvén and fast magnetosonic perturbations. We developed a scenario for the formation of elevated electron temperatures at the equatorward side of the SAPS. It includes a lower‐hybrid drift instability driven by diamagnetic currents, consistent with strong lower‐ and upper‐hybrid plasma wave activity and intense fluxes of the low‐energy electrons and ions near the ring current's inner edge.

Radial diffusion modeling with empirical lifetimes: comparison with CRRES observations

Abstract. A time dependent radial diffusion model is used to quantify the competing effects of inward radial diffusion and losses on the distribution of the outer zone relativistic electrons. The rate of radial diffusion is parameterized by Kp with the loss time as an adjustable parameter. Comparison with HEEF data taken over 500 Combined Release and Radiation Effects Satellite (CRRES) orbits indicates that 1-MeV electron lifetimes near the peak of the outer zone are less than a day during the storm main phase and few days under less disturbed conditions. These values are comparable to independent estimates of the storm time loss rate due to scattering by EMIC waves and chorus emission, and also provide an acceptable representation of electron decay rates following the storm time injection. Although our radial diffusion model, with data derived lifetimes, is able to simulate many features of the variability of outer zone fluxes and predicts fluxes within one order of magnitude accuracy for most of the storms and L values, it fails to reproduce the magnitude of flux changes and the gradual build up of fluxes observed during the recovery phase of many storms. To address these differences future modeling should include an additional local acceleration source and also attempt to simulate the pronounced loss of electrons during the main phase of certain storms.

CRRES electric field power spectra and radial diffusion coefficients

Combined Release and Radiation Effects Satellite (CRRES) Electric Field Instrument (EFI) data are used to determine the electric field power spectral density as a function of L and Kp over the frequency range 0.2 to 15.9 mHz. The power at each frequency is fit to the function P(L, Kp) = a Lb exp(cKp). Assuming a purely electrostatic field and making several other assumptions regarding the azimuthal dependence of the field fluctuations, a Kp‐dependent radial diffusion coefficient DLLE is computed from the power spectra. The model average DLLE for high activity (Kp = 6) are between 1 to 2 orders of magnitude larger than that for low activity (Kp = 1), dependent upon L and first invariant.

Energy-deposition events measured by the CRRES PHA experiment

The energy-deposition spectra measured by the CRRES (Combined Release and Radiation Effects Satellite) pulse height analyzer (PHA) experiment are reexamined to determine the relative contributions from the different mechanisms by which large localized energy-deposition events can be generated in silicon detector volumes flown in space. Comparisons with calculations generated by the CUPID simulation model modified to include pion-production and elastic-scattering events are used to generate a "best fit" trapped proton spectrum that is compared to the predictions of the NASA models for the CRRES orbit.

A statistical study of the global structure of the ring current

In this paper we derive the average configuration of the ring current as a function of the state of the magnetosphere as indicated by the Dst index. We sort magnetic field data from the Combined Release and Radiation Effects Satellite (CRRES) by spatial location and by the Dst index in order to produce magnetic field maps. From these maps we calculate local current systems by taking the curl of the magnetic field. We find both the westward (outer) and the eastward (inner) components of the ring current. We find that the ring current intensity varies linearly with Dst as expected and that the ring current is asymmetric for all Dst values. The azimuthal peak of the ring current is located in the afternoon sector for quiet conditions and near midnight for disturbed conditions. The ring current also moves closer to the Earth during disturbed conditions. We attempt to recreate the Dst index by integrating the magnetic perturbations caused by the ring current. We find that we need to multiply our computed disturbance by a factor of 1.88 ± 0.27 and add an offset of 3.84 ± 4.33 nT in order to get optimal agreement with Dst. When taking into account a tail current contribution of roughly 25%, this agrees well with our expectation of a factor of 1.3 to 1.5 based on a partially conducting Earth. The offset that we have to add does not agree well with an expected offset of approximately 20 nT based on solar wind pressure.

Frequencies of standing Alfvén wave harmonics and their implication for plasma mass distribution along geomagnetic field lines: Statistical analysis of CRRES data

The relationship among the frequencies of the harmonics of standing Alfvén waves depends on the variation of plasma mass density along the geomagnetic field line. This in turn means that observed standing wave frequencies may be used to infer the mass density variation, which is difficult to measure with particle instruments on spacecraft. Determination of the density variation is important in understanding mass transport processes in the ionosphere‐magnetosphere system and also in improving magnetospheric diagnostic techniques using ULF waves. We investigate the frequencies of multiharmonic toroidal standing Alfvén waves detected in the electric and magnetic fields measured by the Combined Release and Radiation Effects Satellite (CRRES). The data cover the entire CRRES mission period from July 1990 to October 1991. Using a semi‐automated procedure, we identify over 4000 samples of the fundamental toroidal frequency (f1), which are often accompanied by the second (f2) and third (f3) harmonics. Most (∼3000) fundamental frequency samples are taken at dipole L shells from 4 to 8 and at magnetic local time (MLT) from 1200 to 1800, and we perform statistical analyses of the frequencies in this L‐MLT domain. The most frequently observed ratios are f2/f1 ∼ 2.5 and f3/f1 ∼ 4.0 for 4 ≤ L < 6 and f2/f1 ∼ 2.8 and f3/f1 ∼ 4.3 for 6 ≤ L < 7. These observations are compared with the theoretical ratios obtained for the density variation of the form ρ = ρeq(LRE/R)α, where ρeq is the equatorial mass density, L is the magnetic shell parameter, R is geocentric distance to the field line, and the power law density index α is a free parameter. We find that α ∼ 0.5 fits the average observed frequency ratios at 4 ≤ L < 6, consistent with a diffusive equilibrium solution. No single value of α fits the average observed frequency ratios at 6 ≤ L < 7. In that case, theoretical solutions indicate that the mass density is locally peaked at the equator; that is, the mass density decreases as one moves off‐equator, then increases again toward the ionosphere. Combined with the results of recent studies of electron density (which have not found such a peak in density at the magnetic equator), this indicates that heavy ions are preferentially concentrated at the magnetic equator.

Magnetospheric toroidal Alfvén wave harmonics and the field line distribution of mass density

Measurements of electric and magnetic field taken by instruments on the Combined Release and Radiation Effects Satellite (CRRES) spacecraft on 29 July 1991 reveal seven or eight toroidal Alfvén wave frequency bands. By using observations of the waves near the magnetic equator and the symmetry of the theoretical modes as a function of magnetic latitude, we can identify which theoretical Alfvén wave harmonic corresponds to a particular frequency band. This, along with the L shell frequency dependence, gives convincing evidence that we are in fact observing the toroidal Alfvén mode. Because the harmonics of the toroidal Alfvén wave have a different response to mass density at different points along a magnetic field line, the frequencies of these harmonics can be used to infer the distribution of mass density along the field line. While there is a significant uncertainty in the results due to the uncertainty in the observed frequencies, it is nevertheless true that both the solution based on the peak (mean) frequencies and the majority of solutions using a Monte Carlo simulation of the effects of uncertainty in frequency show the same result, that there is a local maximum in ρ within about 30° of the magnetic equator. A similar result is found for the wave event observed on 28 August 1990, a local maximum in ρ within about 15° of the magnetic equator. These results imply that heavy ions are preferentially concentrated at the magnetic equator.

A study of Pc-5 ULF oscillations

Abstract. A study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic magnetic field spectrograms have been used to survey ULF pulsation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were examined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probability of occurence of toroidal mode oscillations on the dawn and dusk sides of the magnetosphere inside geosynchronous orbit, while poloidal mode oscillations occur predominantly along the dusk side, consistent with high azimuthal mode number excitation by ring current ions. Pc-5 pulsations following Storm Sudden Commencements (SSCs) were examined separately. The spatial distribution of modes for the SSC events was consistent with the statistical study for the lifetime of CRRES. The toroidal fundamental (and harmonic) resonances are the dominant mode seen on the dawn-side of the magnetosphere following SSCs. Power is mixed in all three components. In the 21 dusk side SSC events there were only a few examples of purely compressional (two) or radial (one) power in the CRRES study, a few more examples of purely toroidal modes (six), with all three components predominant in about half (ten) of the events. Key words. Magnetospheric physics (MHD waves and instabilities; magnetospheric configuration and dynamics) – Space plasma physics (waves and instabilities)

Modeling outer-zone relativistic electron response to whistler-mode chorus activity during substorms

Understanding the behavior of relativistic electrons in the Earth's outer radiation belt during substorms and storms is a current challenge in magnetospheric physics. In this paper, we model energetic electron fluxes at L=5 during the course of three events using wave and particle data from the Combined Release and Radiation Effects Satellite (CRRES). The events comprise a strong magnetic storm with low levels of substorm and chorus wave activity; a moderate storm with enhanced levels of substorm and chorus activity during the recovery phase; and enhanced substorm and chorus activity in the absence of a significant storm signature. Relativistic electron flux enhancements are observed to occur during these events only when substorm and chorus activity are enhanced. We formulate a model kinetic equation for the electron energy distribution incorporating electron acceleration by stochastic gyroresonance with whistler-mode chorus, and electron loss by precipitation due to pitch-angle scattering by plasma waves. The model solutions are found to match reasonably well the CRRES data profiles of the electron differential flux for each event. We conclude that, not only for the events considered but in general, enhanced whistler-mode chorus waves generated during prolonged substorm activity can generate relativistic electron flux increases in the outer radiation zone, whether in the presence or absence of a magnetic storm. We further expect that stochastic acceleration by gyroresonant electron–whistler mode wave interaction could be an important mechanism for generating relativistic electrons during high-intensity long-duration continuous AE activity (HILDCAA) events.

Plasmapause response to geomagnetic storms: CRRES results

The response of the plasmapause following a geomagnetic storm is examined statistically using plasmapause observations made by the Combined Release and Radiation Effects Satellite (CRRES) plasma wave receiver instrument. The plasmapause was identified as the inner most steep density gradient. Due to CRRES' 10‐hour orbital period, the plasmapause is generally sampled at two distinct local time sectors each orbit. The results from a study of 22 storms (with minimum Dst < −30 nT) show that the plasmapause generally moves earthward one L in the night and dawnside following a storm sudden commencement but is highly variable and statistically moves out in the dusk sector. This new result emphasizes that the plasmapause can have significant local time asymmetries that are amplified due to storm dynamics.

Contribution of convective transport to stormtime ring current electron injection

Significant increases in electron fluxes and energy densities at energies from 200 eV to ≥1 MeV have been observed during magnetic storms to L values as low as 2. To investigate the processes responsible for these flux increases of ring current electrons, we simulate the guiding‐center drift and loss of electrons from the plasma sheet to the inner magnetosphere during storms. We use a dipole field plus a constant southward interplanetary magnetic field as our magnetic field model. Over this magnetic field model we impose corotation, quiescent Stern‐Volland, and storm‐associated enhancements in the convection electric field. We perform phase‐space mapping simulations with imposed initial (theoretical results or Combined Release and Radiation Effects Satellite (CRRES) observations) and boundary (averaged Los Alamos National Laboratory/multiple‐particle analyzer or CRRES observations) conditions for hypothetical and real storm events, respectively. Wave‐particle interactions are the dominant loss process for ring current electrons. Wave activity outside the plasmapause is enhanced during storms due to the particle injection from the plasma sheet to the inner magnetosphere during active times. Our loss model takes such enhanced losses into account. We compare our simulated electron fluxes with previously reported fluxes observed by Explorer 45 for hypothetical storms and with in situ fluxes from CRRES/low‐energy plasma analyzer (LEPA) (∼100 eV to ∼20 keV) and CRRES/medium‐energy sensor A (MEA) (153 keV to 1.582 MeV) for two storm events (26 August 1990 and 10 October 1990). We find that direct injection from the plasma sheet by enhanced convection can account for increases in the stormtime ring current electron fluxes from 10 to ∼50 keV. Our simulations quantitatively reproduce the enhanced low‐energy (∼10 keV) electron fluxes observed by CRRES/LEPA at equatorial radial distances of ∼3 to 6.6RE. Our simulated electron fluxes at intermediate energies (∼50 keV) overestimate the corresponding fluxes observed by Explorer 45 at L ∼ 3–5, suggesting that the loss model that we are currently using underestimates the actual electron losses at energies of ∼50 keV. We find that transport via enhanced convection cannot account for the rapid filling of the slot region at 3–5RE for ≥100 keV electrons when we apply linearly interpolated Data Acquisition and Processing Program (DMSP) cross‐polar‐cap potentials in our simple electric field model. However, when we superimpose stormtime fluctuations of the cross‐tail potential drop over linearly interpolated DMSP potentials, we find that the fluxes of electrons are enhanced up to energies of ∼150 keV at L ∼ 3–5RE during the October 1990 event because radial diffusion of the high‐energy electrons during the 22‐hour main phase can be significant. However, it still cannot account for the stormtime flux increases of E ≥ 200 keV at L ∼ 3–5. This may be in part because the simple electric field model that we are using underestimates the electric field intensity in the slot region. Local acceleration mechanisms, which we have not included in our model, may also play an important role.