Transport of the plasma sheet electrons to the geostationary distances

摘要

The transport and acceleration of low-energy electrons (50-250 keV) from the plasma sheet to the geostationary orbit were investigated. Two moderate storm events, which occurred on 6-7 November 1997 and 12-14 June 2005, were modeled using the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM) with the boundary set at 10 RE in the plasma sheet. The output of the IMPTAM was compared to the observed electron fluxes in four energy ranges (50-225 keV) measured by the Synchronous Orbit Particle Analyzer instrument onboard the Los Alamos National Laboratory spacecraft. It was found that the large-scale convection in combination with substorm-associated impulsive fields is the drivers of the transport of plasma sheet electrons from 10 R_E to geostationary orbit at 6.6 R_E during storm times. The addition of radial diffusion had no significant influence on the modeled electron fluxes. At the same time, the modeled electron fluxes are one (two) order(s) smaller than the observed ones for 50-150 keV (150-225 keV) electrons, respectively, most likely due to inaccuracy of electron boundary conditions. The loss processes due to wave-particle interactions were not considered. The choice of the large-scale convection electric field model used in simulations did not have a significant influence on the modeled electron fluxes, since there is not much difference between the equipotential contours given by the Volland-Stern and the Boyle et al. (1997) models at distances from 10 to 6.6 R_E in the plasma sheet. Using the TS05 model for the background magnetic field instead of the T96 model resulted in larger deviations of the modeled electron fluxes from the observed ones due to specific features of the TS05 model. The increase in the modeled electron fluxes can be as large as two orders of magnitude when substorm-associated electromagnetic fields were taken into account. The obtained model distribution of low-energy electron fluxes can be used as an input to the radiation belt models. This seed population for radiation belts will affect the local acceleration up to relativistic energies.