Rapid enhancement of radiation belt electron fluxes due to substorm dipolarization of the geomagnetic field

The classical pure radial diffusion mechanism appears not to fully explain the frequently observed rapid enhancement in the timescales of minutes to h ours in the radiation belt electron fluxes in the Earth's magnetosphere. We here consider other physical mechanisms, such as energization mechanisms a ssociated with substorm processes, to account for these sudden increases. A three-dimensional electron kinetic model is used to simulate the dynamics of the geomagnetically trapped population of radiation belt electrons durin g a substorm injection event. In the past this model has been extensively u sed to study dynamics of energetic ions in the ring current. This work, for the first time, constitutes the development of a combined convection and d iffusion model to radiation belt electrons in the 0.04-4 MeV kinetic energy range. The Tsyganenko 89 geomagnetic field model is used to simulate the t ime-varying terrestrial magnetosphere during the growth phase elongation an d the expansion phase contraction. We find that inductive electric field as sociated with the magnetic reconfiguration process is needed in order to tr ansport substorm electrons into the trapped particle region of the magnetos phere. The maximum enhancement in energetic electron fluxes is found to be located around the geosynchronous orbit location (L = 6.6), with up to 2 or ders of magnitude enhancement in the total fluxes (0.04-4 MeV). Although th is enhancement in the inner magnetosphere is very sensitive to the temperat ure and, to a less extent, density of the source population in the plasma s heet, we suggest that the substorm-associated energization in the magnetota il and the subsequent adiabatic acceleration in the earthward region accoun t for the enhanced MeV electrons (killer electrons) seen at the geosynchron ous orbit during storms and substorms.