Test-Particle Simulation of Storm-Time Outer Radiation Belt: Radial Transport and Losses

During geomagnetic storms relativistic electrons in Earth's outer radiation belt exhibit highly nonlinear behavior. Electron fluxes in the belt vary over several orders in magnitude on the time scales from minutes to days. This work addresses radial transport and losses of radiation belt electrons during storms. For this purpose we developed a new semi-empirical model of the belt. The model is based on a test particle simulations of energetic electron motion in storm-time electric and magnetic fields. Global variations of magnetospheric electric and magnetic fields are derived from a dynamic model of geomagnetic field, for which the inductive electric field is calculated in a self-consistent fashion. We show that impulsive changes in solar wind dynamic pressure can result in rapid electron scattering across the drift shells, which identifies the dynamic pressure as one of the primary mechanisms of radial transport in the belt. Our calculations show that electron motion is inconsistent with radial diffusion, and hence a more detailed description is required for accurate predictions of electron fluxes in the belt. It is also shown that ring current enhancement during storm main phase can produce a substantial impact on electron motion. In particular, during large storms diamagnetic effect due to partial ring current sufficiently changes magnetic field structure in the inner magnetosphere leading to rapid magnetopause losses of radiation belt electrons.