Mechanisms for the acceleration of radiation belt electrons

During the declining phase of the solar cycle fast solar wind streams produce corotating interaction regions (CIRs) that drive moderate geomagnetic storms. These storms often have an unusually long recovery phase and produce high fluxes of relativistic electrons. Here we investigate the physical mechanisms responsible for accelerating electrons to relativistic energies inside the outer radiation belt. We review the most important electron acceleration and loss mechanisms, and present global simulations that combine radial diffusion with acceleration and loss by whistler mode chorus waves. We show that acceleration by chorus waves alone can increase the -MeV electron phase space density between 4.5 < L < 6.5 by up to three orders of magnitude. When radial diffusion and wave acceleration are included accelerated electrons are transported both inwards and outwards and increase the phase space density by a factor of 10 between 3.5 < L < 7. At lower energies of similar to 0.1 to a few hundred keV, chorus waves cause electron precipitation that enhances inward radial diffusion. We conclude that chorus wave acceleration and loss play a major role in the dynamics of the outer radiation belt. We suggest that during the declining phase of the solar cycle Alfvenic wave activity in the fast solar wind provides continuous inward transport of similar to 1-100 keV electrons inside the magnetosphere which maintains whistler mode wave power long enough to accelerate electrons up to similar to MeV energies, and drives radial diffusion to fill up the entire outer radiation belt.

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