Found 919 results
Title: Review of modeling of losses and sources of relativistic electrons in the outer radiation belt II: Local acceleration and loss
Abstract: This paper focuses on the modeling of local acceleration and loss processes in the outer radiation belt. We begin by reviewing the statistical properties of waves that violate the first and second adiabatic invariants, leading to the loss and acceleration of high energy electrons in the outer radiation belt. After a brief description of the most commonly accepted methodology for computing quasi-linear diffusion coefficients, we present pitch-angle scattering simulations by (i) plasmaspheric hiss, (ii) a combination of plasmaspheric hiss and electromagnetic ion cyclotron (EMIC) waves, (iii) chorus waves, and (iv) a combination of chorus and EMIC waves. Simulations of the local acceleration and loss processes show that statistically, the net effect of chorus waves is acceleration at MeV ener. . .
Date: 11/2008 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 1694 - 1713 DOI: 10.1016/j.jastp.2008.06.014 Available at:
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Title: Review of modeling of losses and sources of relativistic electrons in the outer radiation belt I: Radial transport
Abstract: In this paper, we focus on the modeling of radial transport in the Earth's outer radiation belt. A historical overview of the first observations of the radiation belts is presented, followed by a brief description of radial diffusion. We describe how resonant interactions with poloidal and toroidal components of the ULF waves can change the electron's energy and provide radial displacements. We also present radial diffusion and guiding center simulations that show the importance of radial transport in redistributing relativistic electron fluxes and also in accelerating and decelerating radiation belt electrons. We conclude by presenting guiding center simulations of the coupled particle tracing and magnetohydrodynamic (MHD) codes and by discussing the origin of relativistic electrons at ge. . .
Date: 11/2008 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 1679 - 1693 DOI: 10.1016/j.jastp.2008.06.008 Available at:
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Authors: Li W, Shprits Y Y, and Thorne R M
Title: Dynamic evolution of energetic outer zone electrons due to wave-particle interactions during storms
Abstract: [1] Relativistic electrons in the outer radiation belt are subjected to pitch angle and energy diffusion by chorus, electromagnetic ion cyclotron (EMIC), and hiss waves. Using quasi-linear diffusion coefficients for cyclotron resonance with field-aligned waves, we examine whether the resonant interactions with chorus waves produce a net acceleration or loss of relativistic electrons. We also examine the effect of pitch angle scattering by EMIC and hiss waves during the main and recovery phases of a storm. The numerical simulations show that wave-particle interactions with whistler mode chorus waves with realistic wave spectral properties result in a net acceleration of relativistic electrons, while EMIC waves, which provide very fast scattering near the edge of the loss cone, may be a domi. . .
Date: 10/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2007JA012368 Available at:
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Authors: Degeling A W, Rankin R, Kabin K, Marchand R, and Mann I R
Title: The effect of ULF compressional modes and field line resonances on relativistic electron dynamics
Abstract: The adiabatic, drift-resonant interaction between relativistic, equatorially mirroring electrons and a ULF compressional wave that couples to a field line resonance (FLR) is modelled. Investigations are focussed on the effect of azimuthal localisation in wave amplitude on the electron dynamics. The ULF wave fields on the equatorial plane (r , φ ) are modelled using a box model [Zhu, X., Kivelson, M.G., 1988. Analytic formulation and quantitative solutions of the coupled ULF wave problem. J. Geophys. Res. 93(A8), 8602–8612], and azimuthal variations are introduced by adding a discrete spectrum of azimuthal modes. Electron trajectories are calculated using drift equations assuming constant magnetic moment M , and the evolution of the distribution function f(r,φ,M,t) from an assumed in. . .
Date: 04/2007 Publisher: Planetary and Space Science Pages: 731 - 742 DOI: 10.1016/j.pss.2006.04.039 Available at:
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Authors: Chen Yue, Reeves Geoffrey D, and Friedel Reiner H W
Title: The energization of relativistic electrons in the outer Van Allen radiation belt
Abstract: The origin and dynamics of the Van Allen radiation belts is one of the longest-standing questions of the space age, and one that is increasingly important for space applications as satellite systems become more sophisticated, smaller and more susceptible to radiation effects. The precise mechanism by which the Earth's magnetosphere is able to accelerate electrons from thermal to ultrarelativistic energies (Edouble greater than0.5 MeV) has been particularly difficult to definitively resolve. The traditional explanation is that large-scale, fluctuating electric and magnetic fields energize particles through radial diffusion1. More recent theories2, 3 and observations4, 5 have suggested that gyro-resonant wave–particle interactions may be comparable to or more important than radial diffusio. . .
Date: 09/2007 Publisher: Nature Physics Pages: 614 - 617 DOI: 10.1038/nphys655 Available at:
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Authors: Kress B T, Hudson M K, Looper M D, Albert J, Lyon J G, et al.
Title: Global MHD test particle simulations of >10 MeV radiation belt electrons during storm sudden commencement
Abstract: [1] Prior to 2003, there are two known cases where ultrarelativistic (≳10 MeV) electrons appeared in the Earth's inner zone radiation belts in association with high speed interplanetary shocks: the 24 March 1991 and the less well studied 21 February 1994 storms. During the March 1991 event electrons were injected well into the inner zone on a timescale of minutes, producing a new stably trapped radiation belt population that persisted for ∼10 years. More recently, at the end of solar cycle 23, a number of violent geomagnetic disturbances resulted in large variations in ultrarelativistic electrons in the inner zone, indicating that these events are less rare than previously thought. Here we present results from a numerical study of shock-induced transport and energization of outer zone . . .
Date: 09/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA012218 Available at:
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Authors: Reeves Geoffrey D
Title: Radiation Belt Storm Probes: The Next Generation of Space Weather Forecasting
Abstract: N/A
Date: 11/2007 Publisher: Space Weather DOI: 10.1029/2007SW000341 Available at:
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Authors: Thorne R M, Shprits Y Y, Meredith N P, Horne R B, Li W, et al.
Title: Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms
Abstract: [1] Energetic electrons (≥50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies but does not explain the rapid appearance of higher-energy electrons (≥150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enh. . .
Date: 06/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA012176 Available at:
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Authors: MILLAN R, and THORNE R
Title: Review of radiation belt relativistic electron losses
Abstract: We present a brief review of radiation belt electron losses which are vitally important for controlling the dynamics of the radiation belts. A historical overview of early observations is presented, followed by a brief description of important known electron loss mechanisms. We describe key theoretical results and observations related to pitch-angle scattering by resonant interaction with plasmaspheric hiss, whistler-mode chorus and electromagnetic ion cyclotron waves, and review recent work on magnetopause losses. In particular, we attempt to organize recent observational data by loss mechanism and their relative importance to the overall rate of loss. We conclude by suggesting future observational and theoretical work that would contribute to our understanding of this important area of r. . .
Date: 03/2007 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 362 - 377 DOI: 10.1016/j.jastp.2006.06.019 Available at:
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Authors: Meredith Nigel P, Horne Richard B, Glauert Sarah A, and Anderson Roger R
Title: Slot region electron loss timescales due to plasmaspheric hiss and lightning-generated whistlers
Abstract: [1] Energetic electrons (E > 100 keV) in the Earth's radiation belts undergo Doppler-shifted cyclotron resonant interactions with a variety of whistler mode waves leading to pitch angle scattering and subsequent loss to the atmosphere. In this study we assess the relative importance of plasmaspheric hiss and lightning-generated whistlers in the slot region and beyond. Electron loss timescales are determined using the Pitch Angle and energy Diffusion of Ions and Electrons (PADIE) code with global models of the spectral distributions of the wave power based on CRRES observations. Our results show that plasmaspheric hiss propagating at small and intermediate wave normal angles is a significant scattering agent in the slot region and beyond. In contrast, plasmaspheric hiss propagating at large. . .
Date: 08/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2007JA012413 Available at:
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Authors: Summers D., Ni Binbin, and Meredith Nigel P
Title: Timescales for radiation belt electron acceleration and loss due to resonant wave-particle interactions: 1. Theory
Abstract: Radiation belt electrons can interact with various modes of plasma wave in their drift orbits about the Earth, including whistler-mode chorus outside the plasmasphere, and both whistler-mode hiss and electromagnetic ion cyclotron waves inside the plasmasphere. Electrons undergo gyroresonant diffusion in their interactions with these waves. To determine the timescales for electron momentum diffusion and pitch angle diffusion, we develop bounce-averaged quasi-linear resonant diffusion coefficients for field-aligned electromagnetic waves in a hydrogen or multi-ion (H+, He+, O+) plasma. We assume that the Earth's magnetic field is dipolar and that the wave frequency spectrum is Gaussian. Evaluation of the diffusion coefficients requires the solution of a sixth-order polynomial equation for the. . .
Date: 04/2007 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA011801 Available at:
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Authors: Meredith Nigel P, Horne Richard B, Glauert Sarah A, Thorne Richard M, Summers D., et al.
Title: Energetic outer zone electron loss timescales during low geomagnetic activity
Abstract: Following enhanced magnetic activity the fluxes of energetic electrons in the Earth's outer radiation belt gradually decay to quiet-time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 ≤ L ≤ 5.0 occurs during quiet periods (Kp < 3−) following enhanced magnetic activity on timescales ranging from 1.5 to 3.5 days for 214 keV electrons to 5.5 to 6.5 days for 1.09 MeV electrons. The intervals of decay are associated with large average values of the ratio fpe/fce (>7), indicating that the decay takes place in the plasmasphere. We compute loss timescales for pitch-angle scattering by plasmaspheric hiss using the PADIE code with wave properties based on C. . .
Date: 05/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011516 Available at:
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Authors: Bortnik J, Thorne R M, O’Brien T P, Green J C, Strangeway R J, et al.
Title: Observation of two distinct, rapid loss mechanisms during the 20 November 2003 radiation belt dropout event
Abstract: The relativistic electron dropout event on 20 November 2003 is studied using data from a number of satellites including SAMPEX, HEO, ACE, POES, and FAST. The observations suggest that the dropout may have been caused by two separate mechanisms that operate at high and low L-shells, respectively, with a separation at L ∼ 5. At high L-shells (L > 5), the dropout is approximately independent of energy and consistent with losses to the magnetopause aided by the Dst effect and outward radial diffusion which can deplete relativistic electrons down to lower L-shells. At low L-shells (L < 5), the dropout is strongly energy-dependent, with the higher-energy electrons being affected most. Moreover, large precipitation bands of both relativistic electrons and energetic protons are observed at low L. . .
Date: 12/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA011802 Available at:
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Authors: Shprits Y Y, Thorne R M, Friedel R, Reeves G D, Fennell J, et al.
Title: Outward radial diffusion driven by losses at magnetopause
Abstract: Loss mechanisms responsible for the sudden depletions of the outer electron radiation belt are examined based on observations and radial diffusion modeling, with L*-derived boundary conditions. SAMPEX data for October–December 2003 indicate that depletions often occur when the magnetopause is compressed and geomagnetic activity is high, consistent with outward radial diffusion for L* > 4 driven by loss to the magnetopause. Multichannel Highly Elliptical Orbit (HEO) satellite observations show that depletions at higher L occur at energies as low as a few hundred keV, which excludes the possibility of the electromagnetic ion cyclotron (EMIC) wave-driven pitch angle scattering and loss to the atmosphere at L* > 4. We further examine the viability of the outward radial diffusion loss by comp. . .
Date: 11/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA011657 Available at:
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Authors: Iles Roger H A, Meredith Nigel P, Fazakerley Andrew N, and Horne Richard B
Title: Phase space density analysis of the outer radiation belt energetic electron dynamics
Abstract: We present an analysis of the electron phase space density in the Earth's outer radiation belt during three magnetically disturbed periods to determine the likely roles of inward radial diffusion and local acceleration in the energization of electrons to relativistic energies. During the recovery phase of the 9 October 1990 storm and the period of prolonged substorms between 11 and 16 September 1990, the relativistic electron phase space density increases substantially and peaks in the phase space density occur in the region 4.0 < L* < 5.5 for values of the first adiabatic invariant, M ≥ 550 MeV/G, corresponding to energies, E > ∼0.8 MeV. The peaks in the phase space density are associated with prolonged substorm activity, enhanced chorus amplitudes, and predominantly low values of the. . .
Date: 03/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011206 Available at:
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Authors: Fei Yue, Chan Anthony A, Elkington Scot R, and Wiltberger Michael J
Title: Radial diffusion and MHD particle simulations of relativistic electron transport by ULF waves in the September 1998 storm
Abstract: In an MHD particle simulation of the September 1998 magnetic storm the evolution of the radiation belt electron radial flux profile appears to be diffusive, and diffusion caused by ULF waves has been invoked as the probable mechanism. In order to separate adiabatic and nonadiabatic effects and to investigate the radial diffusion mechanism during this storm, in this work we solve a radial diffusion equation with ULF wave diffusion coefficients and a time-dependent outer boundary condition, and the results are compared with the phase space density of the MHD particle simulation. The diffusion coefficients include contributions from both symmetric resonance modes (ω ≈ mωd, where ω is the wave frequency, m is the azimuthal wave number, and ωd is the bounce-averaged drift frequency) and . . .
Date: 12/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011211 Available at:
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Authors: Elkington Scot R, Takahashi K, Chi Peter J, Denton Richard E, and Lysak Robert L
Title: A review of ULF interactions with radiation belt electrons
Abstract: Energetic particle fluxes in the outer zone radiation belts can vary over orders of magnitude on a variety of timescales. Power at ULF frequencies, on the order of a few millihertz, have been associated with changes in flux levels among relativis- tic electrons comprising the outer zone of the radiation belts. Power in this part of the spectrum may occur as a result of a number of processes, including internally- generated waves induced by plasma instabilities, and externally generated processes such as shear instabilities at the flanks or compressive variations in the solar wind. Changes in the large-scale convective motion of the magnetosphere are another important class of externally driven variations with power at ULF wavelengths. The mechanism for interaction between ULF vari. . .
Date: Publisher: American Geophysical Union Pages: 177 - 193 DOI: 10.1029/169GM12 Available at:
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Authors: Sarris T, Li X, and Temerin M
Title: Simulating radial diffusion of energetic (MeV) electrons through a model of fluctuating electric and magnetic fields
Abstract: In the present work, a test particle simulation is performed in a model of analytic Ultra Low Frequency, ULF, perturbations in the electric and magnetic fields of the Earth's magnetosphere. The goal of this work is to examine if the radial transport of energetic particles in quiet-time ULF magnetospheric perturbations of various azimuthal mode numbers can be described as a diffusive process and be approximated by theoretically derived radial diffusion coefficients. In the model realistic compressional electromagnetic field perturbations are constructed by a superposition of a large number of propagating electric and consistent magnetic pulses. The diffusion rates of the electrons under the effect of the fluctuating fields are calculated numerically through the test-particle simulation as a. . .
Date: 10/2006 Publisher: Annales Geophysicae Pages: 2583 - 2598 DOI: 10.5194/angeo-24-2583-2006 Available at:
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Authors: Ukhorskiy A Y, Anderson B J, Brandt P C, and Tsyganenko N A
Title: Storm time evolution of the outer radiation belt: Transport and losses
Abstract: During geomagnetic storms the magnetic field of the inner magnetosphere exhibits large-scale variations over timescales from minutes to days. Being mainly controlled by the magnetic field the motion of relativistic electrons of the outer radiation belt can be highly susceptible to its variations. This paper investigates evolution of the outer belt during the 7 September 2002 storm. Evolution of electron phase space density is calculated with the use of a test-particle simulation in storm time magnetic and electric fields. The results show that storm time intensification of the ring current produces a large impact on the belt. In contrast to the conventional Dst effect the dominant effects are nonadiabatic and lead to profound and irreversible transformations of the belt. The diamagnetic in. . .
Date: 11/2006 Publisher: Journal of Geophysical Research DOI: 10.1029/2006JA011690 Available at:
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Authors: Baker Daniel N., and Lanzerotti Louis
Title: Where Are the "Killer Electrons" of the Declining Phase of Solar Cycle 23
Abstract: “Killer electrons,” enhanced fluxes of radiation belt electrons in the magnetosphere–especially those at geosynchronous orbit (GEO)–were an important space weather phenomenon during the decline to minimum of the last 11-year solar cycle (1993–1995). Indeed, the fluxes of these electrons were reported at the time to have significantly influenced the incidence of anomalies on numerous spacecraft, both commercial and national defense. The incidences of spacecraft anomalies and the “pumping up” of the GEO electron fluxes gave rise to the picture that solar minimum did not provide a benign environment for space-based technologies as had been assumed by many. The decline to minimum of this current (23th) solar cycle has as yet to produce the same number of reported spacecra. . .
Date: 07/2006 Publisher: Space Weather DOI: 10.1029/2006SW000259 Available at:
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Authors: Albert J M
Title: Evaluation of quasi-linear diffusion coefficients for whistler mode waves in a plasma with arbitrary density ratio
Abstract: Techniques are presented for efficiently evaluating quasi-linear diffusion coefficients for whistler mode waves propagating according to the full cold plasma index of refraction. In particular, the density ratio ωpe/Ωe can be small, which favors energy diffusion. This generalizes an approach, previously used for high-density hiss and electromagnetic ion cyclotron waves, of identifying (and omitting) ranges of wavenormal angle θ that are incompatible with cyclotron resonant frequencies ω occurring between sharp cutoffs of the modeled wave frequency spectrum. This requires a detailed analysis of the maximum and minimum values of the refractive index as a function of ω and θ, as has previously been performed in the high-density approximation. Sample calculations show the effect of low-d. . .
Date: 03/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2004JA010844 Available at:
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Authors: Ukhorskiy A Y, Takahashi K, Anderson B. J., and Korth H.
Title: Impact of toroidal ULF waves on the outer radiation belt electrons
Abstract: Relativistic electron fluxes in the outer radiation belt exhibit highly variable complex behavior. Previous studies have established a strong correlation of electron fluxes and the inner magnetospheric ULF waves in the Pc 3–5 frequency range. Resonant interaction of ULF waves with the drift motion of radiation belt electrons violates their third adiabatic invariant and consequently leads to their radial transport. If the wave-particle interaction has a stochastic character, then the electron transport is diffusive. The goal of this paper is to analyze the impact of toroidal ULF waves on radiation belt electrons. The study is based on direct measurements of ULF electric fields on the CRRES spacecraft. We show that the electric fields of inner magnetospheric toroidal ULF waves exhibit high. . .
Date: 10/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2005JA011017 Available at:
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Authors: Perry K L, Hudson M K, and Elkington S. R.
Title: Incorporating spectral characteristics of Pc5 waves into three-dimensional radiation belt modeling and the diffusion of relativistic electrons
Abstract: The influence of ultralow frequency (ULF) waves in the Pc5 frequency range on radiation belt electrons in a compressed dipole magnetic field is examined. This is the first analysis in three dimensions utilizing model ULF wave electric and magnetic fields on the guiding center trajectories of relativistic electrons. A model is developed, describing magnetic and electric fields associated with poloidal mode Pc5 ULF waves. The frequency and L dependence of the ULF wave power are included in this model by incorporating published ground-based magnetometer data. It is demonstrated here that realistic spectral characteristics play a significant role in the rate of diffusion of relativistic electrons via drift resonance with poloidal mode ULF waves. Radial diffusion rates including bounce motion s. . .
Date: 03/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2004JA010760 Available at:
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Authors: Mithaiwala M J, and Horton W.
Title: Substorm injections produce sufficient electron energization to account for MeV flux enhancements following some storms
Abstract: One of the main questions concerning radiation belt research is the origin of very high energy (>1 MeV) electrons following many space storms. Under the hypothesis that the plasma sheet electron population is the source of these electrons, which are convected to the outer radiation belt region during substorms, we estimate the flux of particles generated at geosynchronous orbit. We use the test particle method of following guiding center electrons as they drift in the electromagnetic fields during substorm dipolarization. The dipolarization pulse model electromagnetic fields are taken from the Li et al. (1998) substorm particle injection model. We find that a substorm dipolarization can produce enough electrons within geosynchronous orbit to account for the electrons seen following storms.. . .
Date: 07/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2004JA010511 Available at:
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Authors: Thorne R M, O'Brien T. P., Shprits Y. Y., Summers D., and Horne R. B.
Title: Timescale for MeV electron microburst loss during geomagnetic storms
Abstract: Energetic electrons in the outer radiation belt can resonate with intense bursts of whistler-mode chorus emission leading to microburst precipitation into the atmosphere. The timescale for removal of outer zone MeV electrons during the main phase of the October 1998 magnetic storm has been computed by comparing the rate of microburst loss observed on SAMPEX with trapped flux levels observed on Polar. Effective lifetimes are comparable to a day and are relatively independent of L shell. The lifetimes have also been evaluated by theoretical calculations based on quasi-linear scattering by field-aligned waves. Agreement with the observations requires average wide-band wave amplitudes comparable to 100 pT, which is consistent with the intensity of chorus emissions observed under active conditi. . .
Date: 09/2005 Publisher: Journal of Geophysical Research DOI: 10.1029/2004JA010882 Available at:
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Authors: Horne Richard B, Thorne Richard M, Shprits Yuri Y, Meredith Nigel P, Glauert Sarah A, et al.
Title: Wave acceleration of electrons in the Van Allen radiation belts
Abstract: The Van Allen radiation belts1 are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar activity2, 3 and they represent a hazard to satellites and humans in space4, 5. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth6, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase . . .
Date: 09/2005 Publisher: Nature Pages: 227 - 230 DOI: 10.1038/nature03939 Available at:
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Authors: Baker D N, Kanekal S G, Li X, Monk S P, Goldstein J, et al.
Title: An extreme distortion of the Van Allen belt arising from the ‘Hallowe’en’ solar storm in 2003
Abstract: The Earth's radiation belts—also known as the Van Allen belts1—contain high-energy electrons trapped on magnetic field lines2, 3. The centre of the outer belt is usually 20,000–25,000 km from Earth. The region between the belts is normally devoid of particles2, 3, 4, and is accordingly favoured as a location for spacecraft operation because of the benign environment5. Here we report that the outer Van Allen belt was compressed dramatically by a solar storm known as the ‘Hallowe'en storm’ of 2003. From 1 to 10 November, the outer belt had its centre only ~10,000 km from Earth's equatorial surface, and the plasmasphere was similarly displaced inwards. The region between the belts became the location of high particle radiation intensity. This remarkable deformation of the entire. . .
Date: 12/2004 Publisher: Nature Pages: 878 - 881 DOI: 10.1038/nature03116 Available at:
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Authors: O’Brien T P, Looper M. D., and Blake J. B.
Title: Quantification of relativistic electron microburst losses during the GEM storms
Abstract: Bursty precipitation of relativistic electrons has been implicated as a major loss process during magnetic storms. One type of precipitation, microbursts, appears to contain enough electrons to empty the prestorm outer radiation belt in approximately a day. During storms that result in high fluxes of trapped relativistic electrons, microbursts continue for several days into the recovery phase, when trapped fluxes are dramatically increasing. The present study shows that this apparent inconsistency is resolved by observations that the number of electrons lost through microbursts is 10–100 times larger during the main phase than during the recovery phase of several magnetic storms chosen by the Geospace Environment Modeling (GEM) program.
Date: 02/2004 Publisher: Geophysical Research Letters DOI: 10.1029/2003GL018621 Available at:
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Authors: Green Janet C, and Kivelson M. G.
Title: Relativistic electrons in the outer radiation belt: Differentiating between acceleration mechanisms
Abstract: Many theoretical models have been developed to explain the rapid acceleration to relativistic energies of electrons that form the Earth's radiation belts. However, after decades of research, none of these models has been unambiguously confirmed by comparison to observations. Proposed models can be separated into two types: internal and external source acceleration mechanisms. Internal source acceleration mechanisms accelerate electrons already present in the inner magnetosphere (L < 6.6), while external source acceleration mechanisms transport and accelerate a source population of electrons from the outer to the inner magnetosphere. In principle, the two types of acceleration mechanisms can be differentiated because they imply that different radial gradients of electron phase space density. . .
Date: 03/2004 Publisher: Journal of Geophysical Research DOI: 10.1029/2003JA010153 Available at:
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Authors: Shprits Y Y, and Thorne R. M.
Title: Time dependent radial diffusion modeling of relativistic electrons with realistic loss rates
Abstract: Model simulations are compared to the typically observed evolution of MeV electron fluxes during geomagnetic storms to investigate whether radial diffusion alone can account for the observed variability and to estimate the effect of electron lifetimes. We demonstrate that knowledge of lifetimes is crucial for understanding the radial structure of the storm-time radiation belts and their temporal evolution. Our model results suggest that outer zone lifetimes at 1 MeV are on the order of few days during quite-times and less than a day during storm-time conditions. Losses outside plasmasphere should be included in the modeling of electron fluxes since effective lifetimes are much shorter than that of plasmaspheric losses. Simulations with variable outer boundary conditions show that the deple. . .
Date: 04/2004 Publisher: Geophysical Research Letters DOI: 10.1029/2004GL019591 Available at:
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Authors: O’Brien T P, Lorentzen K. R., Mann I. R., Meredith N. P., Blake J. B., et al.
Title: Energization of relativistic electrons in the presence of ULF power and MeV microbursts: Evidence for dual ULF and VLF acceleration
Abstract: We examine signatures of two types of waves that may be involved in the acceleration of energetic electrons in Earth's outer radiation belts. We have compiled a database of ULF wave power from SAMNET and IMAGE ground magnetometer stations for 1987–2001. Long-duration, comprehensive, in situ VLF/ELF chorus wave observations are not available, so we infer chorus wave activity from low-altitude SAMPEX observations of MeV electron microbursts for 1996–2001 since microbursts are thought to be caused by interactions between chorus and trapped electrons. We compare the ULF and microburst observations to in situ trapped electrons observed by high-altitude satellites from 1989–2001. We find that electron acceleration at low L shells is closely associated with both ULF activity and MeV microbu. . .
Date: 08/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2002JA009784 Available at:
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Authors: Albert J M
Title: Evaluation of quasi-linear diffusion coefficients for EMIC waves in a multispecies plasma
Abstract: Quasi-linear velocity-space diffusion coefficients due to L-mode electromagnetic ion cyclotron (EMIC) waves are considered in a multispecies plasma. It is shown, with slight approximations to exact cold plasma theory, that within EMIC pass bands the index of refraction is a monotonically increasing function of frequency. Analytical criteria are then derived which identify ranges of latitude, wavenormal angle, and resonance number consistent with resonance in a prescribed wave population. This leads to computational techniques which allow very efficient calculation of the diffusion coefficients, along the lines previously developed for whistler and ion cyclotron waves in an electron-proton plasma. The techniques are applied to radiation belt electrons at L = 4, for EMIC waves in the hydroge. . .
Date: 06/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2002JA009792 Available at:
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Authors: Meredith Nigel P, Cain Michelle, Horne Richard B., Thorne Richard M., Summers D., et al.
Title: Evidence for chorus-driven electron acceleration to relativistic energies from a survey of geomagnetically disturbed periods
Abstract: We perform a survey of the plasma wave and particle data from the CRRES satellite during 26 geomagnetically disturbed periods to investigate the viability of a local stochastic electron acceleration mechanism to relativistic energies driven by Doppler-shifted cyclotron resonant interactions with whistler mode chorus. Relativistic electron flux enhancements associated with moderate or strong storms may be seen over the whole outer zone (3 < L < 7), typically peaking in the range 4 < L < 5, whereas those associated with weak storms and intervals of prolonged substorm activity lacking a magnetic storm signature (PSALMSS) are typically observed further out in the regions 4 < L < 7 and 4.5 < L < 7, respectively. The most significant relativistic electron flux enhancements are seen outside of th. . .
Date: 06/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2002JA009764 Available at:
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Authors: Miyoshi Yoshizumi
Title: Rebuilding process of the outer radiation belt during the 3 November 1993 magnetic storm: NOAA and Exos-D observations
Abstract: Using the data from the NOAA and Exos-D satellites during the 3 November 1993 magnetic storm, the dynamic behavior of electrons with energies from a few tens of kiloelectronvolts to a few and its relation to plasma waves were examined. After the late main phase, relativistic electron flux started to recover from the heart of the outer radiation belt, where the cold plasma density was extremely low, and intense whistler mode chorus emissions were detected. The phase space density showed a peak in the outer belt, and the peak increased gradually. The simulation of the inward radial diffusion process could not reproduce the observed energy spectrum and phase space density variation. On the other hand, the simulated energy diffusion due to the gyroresonant electron-whistler mode wave interacti. . .
Date: 03/2003 Publisher: Journal of Geophysical Research Pages: SMP 3-1–SMP 3-15 DOI: 10.1029/2001JA007542 Available at:
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Authors: Horne R B
Title: Relativistic electron acceleration and precipitation during resonant interactions with whistler-mode chorus
Abstract: 1] Resonant interactions with whistler-mode chorus waves provide an important process for electron loss and acceleration during storm times. We demonstrate that wave propagation significantly affects the electron scattering rates. We show that stormtime chorus waves outside the plasmapause can scatter equatorial electrons ≤60 keV into the loss cone and accelerate trapped electrons up to ∼ MeV energies at large pitch-angles. Using ray tracing to map the waves to higher latitudes, we show that the decrease in the ratio between the electron plasma and gyro frequencies, along with the normalized chorus frequency bandwidth, enable much higher energy electrons ∼1 MeV to be scattered into the loss cone. We suggest that off equatorial pitch-angle scattering by chorus waves is responsible for. . .
Date: 05/2003 Publisher: Geophysical Research Letters DOI: 10.1029/2003GL016973 Available at:
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Authors: Summers D.
Title: Relativistic electron pitch-angle scattering by electromagnetic ion cyclotron waves during geomagnetic storms
Abstract: [1] During magnetic storms, relativistic electrons execute nearly circular orbits about the Earth and traverse a spatially confined zone within the duskside plasmapause where electromagnetic ion cyclotron (EMIC) waves are preferentially excited. We examine the mechanism of electron pitch-angle diffusion by gyroresonant interaction with EMIC waves as a cause of relativistic electron precipitation loss from the outer radiation belt. Detailed calculations are carried out of electron cyclotron resonant pitch-angle diffusion coefficients Dαα for EMIC waves in a multi-ion (H+, He+, O+) plasma. A simple functional form for Dαα is used, based on quasi-linear theory that is valid for parallel-propagating, small-amplitude electromagnetic waves of general spectral density. For typical observed EM. . .
Date: 04/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2002JA009489 Available at:
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Authors: Elkington Scot R
Title: Resonant acceleration and diffusion of outer zone electrons in an asymmetric geomagnetic field
Abstract: [1] The outer zone radiation belt consists of energetic electrons drifting in closed orbits encircling the Earth between ∼3 and 7 RE. Electron fluxes in the outer belt show a strong correlation with solar and magnetospheric activity, generally increasing during geomagnetic storms with associated high solar wind speeds, and increasing in the presence of magnetospheric ULF waves in the Pc-5 frequency range. In this paper, we examine the influence of Pc-5 ULF waves on energetic electrons drifting in an asymmetric, compressed dipole and find that such particles may be efficiently accelerated through a drift-resonant interaction with the waves. We find that the efficiency of this acceleration increases with increasing magnetospheric distortion (such as may be attributed to increased solar win. . .
Date: 03/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2001JA009202 Available at:
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Authors: Meredith Nigel P
Title: Statistical analysis of relativistic electron energies for cyclotron resonance with EMIC waves observed on CRRES
Abstract: Electromagnetic ion cyclotron (EMIC) waves which propagate at frequencies below the proton gyrofrequency can undergo cyclotron resonant interactions with relativistic electrons in the outer radiation belt and cause pitch-angle scattering and electron loss to the atmosphere. Typical storm-time wave amplitudes of 1–10 nT cause strong diffusion scattering which may lead to significant relativistic electron loss at energies above the minimum energy for resonance, Emin. A statistical analysis of over 800 EMIC wave events observed on the CRRES spacecraft is performed to establish whether scattering can occur at geophysically interesting energies (≤2 MeV). While Emin is well above 2 MeV for the majority of these events, it can fall below 2 MeV in localized regions of high plasma density and/o. . .
Date: 06/2003 Publisher: Journal of Geophysical Research DOI: 10.1029/2002JA009700 Available at:
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Authors: ELKINGTON S, Hudson M K, Wiltberger M J, and Lyon J G
Title: MHD/particle simulations of radiation belt dynamics
Abstract: Particle fluxes in the outer radiation belts can show substantial variation in time, over scales ranging from a few minutes, such as during the sudden commencement phase of geomagnetic storms, to the years-long variations associated with the progression of the solar cycle. As the energetic particles comprising these belts can pose a hazard to human activity in space, considerable effort has gone into understanding both the source of these particles and the physics governing their dynamical behavior. Computationally tracking individual test particles in a model magnetosphere represents a very direct, physically-based approach to modeling storm-time radiation belt dynamics. Using global magnetohydrodynamic models of the Earth–Sun system coupled with test particle simulations of the radiati. . .
Date: 04/2002 Publisher: Journal of Atmospheric and Solar-Terrestrial Physics Pages: 607 - 615 DOI: 10.1016/S1364-6826(02)00018-4 Available at:
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Authors: Millan R M
Title: X-ray observations of MeV electron precipitation with a balloon-borne germanium spectrometer
Abstract: The high-resolution germanium detector aboard the MAXIS (MeV Auroral X-ray Imaging and Spectroscopy) balloon payload detected nine X-ray bursts with significant flux extending above 0.5 MeV during an 18 day flight over Antarctica. These minutes-to-hours-long events are characterized by an extremely flat spectrum (∼E−2) similar to the first MeV event discovered in 1996, indicating that the bulk of parent precipitating electrons is at relativistic energies. The MeV bursts were detected between magnetic latitudes 58°–68° (L-values of 3.8–6.7) but only in the late afternoon/dusk sectors (14:30–00:00 MLT), suggesting scattering by EMIC (electromagnetic ion cyclotron) waves as a precipitation mechanism. We estimate the average flux of precipitating E ≥ 0.5 MeV electrons to be ∼36. . .
Date: 12/2002 Publisher: Geophysical Research Letters DOI: 10.1029/2002GL015922 Available at:
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Authors: Ingraham J C, Cayton T E, Belian R D, Christensen R A, Friedel R H W, et al.
Title: Substorm injection of relativistic electrons to geosynchronous orbit during the great magnetic storm of March 24, 1991
Abstract: The great March 1991 magnetic storm and the immediately preceding solar energetic particle event (SEP) were among the largest observed during the past solar cycle, and have been the object of intense study. We investigate here, using data from eight satellites, the very large delayed buildup of relativistic electron flux in the outer zone during a 1.5-day period beginning 2 days after onset of the main phase of this storm. A notable feature of the March storm is the intense substorm activity throughout the period of the relativistic flux buildup, and the good correlation between some temporal features of the lower-energy substorm-injected electron flux and the relativistic electron flux at geosynchronous orbit. Velocity dispersion analysis of these fluxes between geosynchronous satellites . . .
Date: 11/2001 Publisher: Journal of Geophysical Research Pages: 25759 - 25776 DOI: 10.1029/2000JA000458 Available at:
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Authors: Brautigam D H, and Albert J M
Title: Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm
Abstract: The response of outer radiation belt relativistic electrons to the October 9, 1990, magnetic storm is analyzed in detail using a radial diffusion model and data from the Combined Release and Radiation Effects Satellite (CRRES) and the Los Alamos National Laboratory (LANL) geosynchronous satellite 1989-046. Electron measurements are expressed in terms of phase space density as a function of the three adiabatic invariants determined from CRRES magnetic field data and the Tsyganenko 1989 Kp-dependent magnetic field model. The radial diffusion model is implemented with a time-dependent radial diffusion coefficient parameterized by Kp, and a time-dependent outer boundary condition scaled by geosynchronous electron data. The results show that radial diffusion propagates outer boundary variations. . .
Date: 01/2000 Publisher: Journal of Geophysical Research Pages: 291 DOI: 10.1029/1999JA900344 Available at:
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Authors: Desorgher L, ühler P, Zehnder A, and ückiger E O
Title: Simulation of the outer radiation belt electron flux decrease during the March 26, 1995, magnetic storm
Abstract: In this paper we study the variation of the relativistic electron fluxes in the Earth's outer radiation belt during the March 26, 1995, magnetic storm. Using observations by the radiation environment monitor (REM) on board the space technology research vehicle (STRV-Ib), we discuss the flux decrease and possible loss of relativistic electrons during the storm main phase. In order to explain the observations we have performed fully adiabatic and guiding center simulations for relativistic equatorial electrons in the nonstationary Tsygarienko96 magnetospheric magnetic field model. In our simulations the drift of electrons through the magnetopause was considered as a loss process. We present our model results and discuss their dependence on the magnetospheric magnetic and electric field model. . .
Date: 09/2000 Publisher: Journal of Geophysical Research Pages: 21211 DOI: 10.1029/2000JA900060 Available at:
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Authors: Meredith Nigel P, Horne Richard B, Johnstone Alan D, and Anderson Roger R
Title: The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere
Abstract: The temporal evolution of electron distributions and associated wave activity following substorm injections in the inner magnetosphere are investigated using data from the CRRES satellite. Equatorial electron distributions and concomitant wave spectra outside the plasmapause on the nightside of the Earth are studied as a function of time since injection determined from the auroral-electrojet index (AE). The electron cyclotron harmonic (ECH) wave amplitudes are shown to be very sensitive to small modeling errors in the location of the magnetic equator. They are best understood at the ECH equator, defined by the local maximum in the ECH wave activity in the vicinity of the nominal magnetic equator, suggesting that the ECH equator is a better measure of the location of the true equator. Stron. . .
Date: 06/2000 Publisher: Journal of Geophysical Research Pages: 12907 DOI: 10.1029/2000JA900010 Available at:
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Authors: Elkington Scot R, Hudson M K, and Chan Anthony A
Title: Acceleration of relativistic electrons via drift-resonant interaction with toroidal-mode Pc-5 ULF oscillations
Abstract: There has been increasing evidence that Pc-5 ULF oscillations play a fundamental role in the dynamics of outer zone electrons. In this work we examine the adiabatic response of electrons to toroidal-mode Pc-5 field line resonances using a simplified magnetic field model. We find that electrons can be adiabatically accelerated through a drift-resonant interaction with the waves, and present expressions describing the resonance condition and half-width for resonant interaction. The presence of magnetospheric convection electric fields is seen to increase the rate of resonant energization, and allow bulk acceleration of radiation belt electrons. Conditions leading to the greatest rate of acceleration in the proposed mechanism, a nonaxisymmetric magnetic field, superimposed toroidal oscillatio. . .
Date: 11/1999 Publisher: Geophysical Research Letters Pages: 3273 DOI: 10.1029/1999GL003659 Available at:
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Authors: Burch L, Carovillano L, Antiochos K, Hudson M K, Elkington S R, et al.
Title: Simulation of Radiation Belt Dynamics Driven by Solar Wind Variations
Abstract: The rapid rise of relativistic electron fluxes inside geosynchronous orbit during the January 10-11, 1997, CME-driven magnetic cloud event has been simulated using a relativistic guiding center test particle code driven by out-put from a 3D global MHD simulation of the event. A comparison can be made of this event class, characterized by a moderate solar wind speed (< 600 km/s), and those commonly observed at the last solar maximum with a higher solar wind speed and shock accelerated solar energetic proton component. Relativistic electron flux increase occurred over several hours for the January event, during a period of prolonged southward IMF Bz more rapidly than the 1-2 day delay typical of flux increases driven by solar wind high speed stream interactions. Simulations of th. . .
Date: Publisher: American Geophysical Union Pages: 171 - 182 DOI: 10.1029/GM10910.1029/GM109p0171 Available at:
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Authors: Abel Bob, and Thorne Richard M
Title: Electron scattering loss in Earth’s inner magnetosphere 1. Dominant physical processes
Abstract: Pitch angle diffusion rates due to Coulomb collisions and resonant interactions with plasmaspheric hiss, lightning-induced whistlers and anthropogenic VLF transmissions are computed for inner magnetospheric electrons. The bounce-averaged, quasi-linear pitch angle diffusion coefficients are input into a pure pitch angle diffusion equation to obtain L and energy dependent equilibrium distribution functions and precipitation lifetimes. The relative effects of each scattering mechanism are considered as a function of electron energy and L shell. Model calculations accurately describe the enhanced loss rates in the slot region, as well as reduced scattering in the heavily populated inner radiation belt. Predicted electron distribution function calculations in the slot region display a character. . .
Date: 02/1998 Publisher: Journal of Geophysical Research Pages: 2385 - 2396 DOI: 10.1029/97JA02919 Available at:
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Authors: Summers D., Thorne Richard M, and Xiao Fuliang
Title: Relativistic theory of wave-particle resonant diffusion with application to electron acceleration in the magnetosphere
Abstract: Resonant diffusion curves for electron cyclotron resonance with field-aligned electromagnetic R mode and L mode electromagnetic ion cyclotron (EMIC) waves are constructed using a fully relativistic treatment. Analytical solutions are derived for the case of a single-ion plasma, and a numerical scheme is developed for the more realistic case of a multi-ion plasma. Diffusion curves are presented, for plasma parameters representative of the Earth's magnetosphere at locations both inside and outside the plasmapause. The results obtained indicate minimal electron energy change along the diffusion curves for resonant interaction with L mode waves. Intense storm time EMIC waves are therefore ineffective for electron stochastic acceleration, although these waves could induce rapid pitch angle scat. . .
Date: 09/1998 Publisher: Journal of Geophysical Research Pages: 20487 - 20500 DOI: 10.1029/98JA01740 Available at:
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Authors: Birn J, Thomsen M F, Borovsky J E, Reeves G D, McComas D J, et al.
Title: Substorm electron injections: Geosynchronous observations and test particle simulations
Abstract: We investigate electron acceleration and the flux increases associated with energetic electron injections on the basis of geosynchronous observations and test-electron orbits in the dynamic fields of a three-dimensional MHD simulation of neutral line formation and dipolarization in the magnetotail. This complements an earlier investigation of test protons [Birn et al., 1997b]. In the present paper we consider equatorial orbits only, using the gyrocenter drift approximation. It turns out that this approximation is valid for electrons prior to and during the flux rises observed in the near tail region of the model at all energies considered (∼ 100 eV to 1 MeV). The test particle model reproduces major observed characteristics: a fast flux rise, comparable to that of the ions, and the exist. . .
Date: 05/1998 Publisher: Journal of Geophysical Research Pages: 9235 - 9248 DOI: 10.1029/97JA02635 Available at:
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Authors: Li Xinlin, Baker D N, Temerin M, Cayton T E, Reeves E G D, et al.
Title: Multisatellite observations of the outer zone electron variation during the November 3–4, 1993, magnetic storm
Abstract: The disappearance and reappearance of outer zone energetic electrons during the November 3–4, 1993, magnetic storm is examined utilizing data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the Global Positioning System (GPS) series, and the Los Alamos National Laboratory (LANL) sensors onboard geosynchronous satellites. The relativistic electron flux drops during the main phase of the magnetic storm in association with the large negative interplanetary Bz and rapid solar wind pressure increase late on November 3. Outer zone electrons with E > 3 MeV measured by SAMPEX disappear for over 12 hours at the beginning of November 4. This represents a 3 orders of magnitude decrease down to the cosmic ray background of the detector. GPS and LANL sensors show similar eff. . .
Date: 01/1997 Publisher: Journal of Geophysical Research Pages: 14123 - 14140 DOI: 10.1029/97JA01101 Available at:
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