Contribution of convective transport to stormtime ring current electron injection

Abstract

[1] 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 6.6R E . 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 3-5R E 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 $ 3-5R E 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. L...

Prompt energization of relativistic and highly relativistic electrons during a substorm interval: Van Allen Probes observations

“…They form the seed population that is essential for the ultimate radiation belt enhancements. Electrons with relativistic energies >500 keV are mostly gradient and curvature drifting and convection cannot inject them far inward [e.g., Liu et al, 2003]. Another difference is that above a few MeV, electrons are not effectively scattered by whistler mode chorus, and thus, quasi-linear diffusive local acceleration by chorus band waves is not likely to be efficient.…”

Relative contribution of electrons to the stormtime total ring current energy content

“…In the inner magnetosphere, electrons drift eastward while ions westward because of the magnetic gradient and curvature drift. Liu et al [2003] show that major stormtime enhancements of electron fluxes can occur on the dawn side. In addition, ions with E k > 30 keV have no access to dawn during the storm main phase [Korth et al, 2000].…”

“…We briefly describe our ring current electron [Liu et al, 2003] and ring current ion [Chen et al, 1994] simulation models. More complete description can be found in the above mentioned references.…”

“…We consider the proton loss due to charge exchange (see Chen et al [1994] for details). For electrons, we consider losses due to wave-particle interactions (see Liu et al [2003] for details).…”

“…We use an electron ring current simulation model [Liu et al, 2003] that we recently developed and the proton ring current simulation model of Chen et al [1994Chen et al [ , 2003. The ring current simulation model of Liu et al [2003] successfully reproduced stormtime electron fluxes at $12 keV that were measured by the CRRES satellite at 3 L 6 during two storm events. We will simulate the energy content of both electrons and protons for a model storm and use the results to estimate the relative contribution of stormtime ring current electrons to the total ring current energy content.…”