Electron flux changes in the outer radiation belt by radial diffusion during the storm recovery phase in comparison with the fully adiabatic evolution

Abstract

[1] The radial diffusion process can play an important role in redistributing the radiation belt electron fluxes. In this work, we have performed 1-D radial diffusion simulations to examine the evolution of the phase space density (PSD) of the outer radiation belt electrons and to estimate the corresponding fluxes during the storm recovery phase. The key element that distinguishes our simulations from previous works is the initial condition for PSD, which is characterized by a steep radial gradient across the trapping boundary. In our simulations, this condition is formed as a result of the drift loss effect of particles during the storm main phase, and the simulations of radial diffusion were run for the storm recovery phase. We performed the study for three classes of geomagnetic storms of different intensities, i.e., the moderate (−100 nT < Dstmin ≤ −50 nT), strong (−150 nT < Dstmin ≤ −100 nT), and severe (Dstmin ≤ −150 nT) storms. The effects of radial diffusion in PSD are notable in the following respects. First, the radial diffusion process is very significant for the initial few hours of the storm recovery phase. Second, the effect of the radial diffusion occurs in both inward and outward directions, thus affecting a wide range of L regions. The inward diffusion causes the PSD peak to move inward. The regions outside of the initial trapping boundary are refilled with finite PSD by the outward radial diffusion. Consequently, the combination of these effects results in different levels and patterns in the directional and omni-directional fluxes from those expected from a fully adiabatic evolution throughout the entire storm period. Last, the details of the PSD evolution, and thus its effect on the corresponding flux levels and patterns, differ among storms of different intensities. We report these differences in detail.