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. (C) 2003 Elsevier Ltd. All rights reserved.