Evolution of electron fluxes in the outer radiation beltcomputed with the VERB code

摘要

Three-dimensional simulations of the dynamics of outer radiation belt electrons withthe recently developed Versatile Electron Radiation Belt (VERB) code are presented.Simulations are preformed for an idealized storm with geomagnetic activity—dependentwave amplitudes that are parameterized as a function of the level of geomagnetic activity.Numerical experiments using the VERB code with various scattering processes (pitchangle diffusion, radial diffusion, and energy diffusion) indicate that diffusive processes arestrongly coupled with each other and that they all should be included in realisticsimulations of the radiation belts. We show that during storms, inward radial diffusion canproduce significant accelerations to relativistic energies, while pitch angle scattering and energy diffusion produce a decrease and an increase in fluxes, respectively. We showthat in the presence of high-latitude and low-latitude chorus, peaks in the radial profileof phase space density are formed between L of 4 and 6 during the recovery phase of astorm and are later smoothed by radial diffusion. Sensitivity experiments show thatgeomagnetic control of wave intensities plays a controlling role in the dynamics ofradiation belt electrons. Numerical simulations indicate that electrons of 10-100 keV neargeosynchronous orbit can reach MeV energies in the heart of the radiation belts bycombined radial diffusion and in situ acceleration. We present two scenarios ofacceleration of the plasma sheet electrons: (1) in the range of hundreds of keV by meansof radial diffusion and (2) in the range of tens of keV by means of radial diffusioncombined with local acceleration.