Authors

S. Liu1,M. W. Chen2, L. R. Lyons1,H. Korth3,J. M. Albert4,J. L. Roeder3,P. C. Anderson2,M. F. Thomsen5

1  Department of Atmospheric Sciences
University of California, Los Angeles
Los Angeles, CA 90095-1565

3  2Space Science Applications Laboratory, M2-260
The Aerospace Corporation
6P. O. Box 92957, Los Angeles, CA 90009

2  Department of Physics
The Johns Hopkins University, Applied Physics Laboratory
11100 Johns Hopkins Rd.
Laurel, MD 20723-6099

4  Air Force Research Lab/VSB
29 Randolph Rd.
Hanscom AFB, MA 01731-3010

Geophys. Res. Lett., 32, L03110, doi: 10.1029/2004GL021672, 2005.

Abstract

Significant increases in electron fluxes and energy densities at energies from 200 eV to ¡Ý 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 IMF 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 CRRES observations) and boundary (averaged LANL/MPA 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/LEPA (~100 eV to ~20 keV) and CRRES/MEA (153 keV to 1.582 MeV) for two storm events (August 26, 1990; and October 10, 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 6.6 RE. 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 3-5 RE for ¡Ý 100 keV electrons when we apply linearly interpolated 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 ~3-5 RE during the October 1990 event because radial diffusion of the high-energy electrons during the 22-h main phase can be significant. However, it still cannot account for the stormtime flux increases of E ¡Ý 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.

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