Modeling the radiation belts: What are the important physical processes to be taken into account in models?

During active periods, physical processes acting on particle dynamics are well known to have several origins and can play a role at different times, different locations, and with different time scales. As their effects can be opposite, it is necessary to identify them and their relative importance: - the particle sources (plasmasheet or direct solar wind entry) - the particle losses (precipitation or drift loss) - the particle transport and acceleration (convection access, magnetic or electric pulse or variation and recirculation). The various phenomena are explained and results are presented. In particular, we demonstrate that classical diffusion models like the Salammbo code can account for all these phenomena. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.