SIMULATIONS OF RADIATION BELT FORMATION DURING STORM SUDDEN COMMENCEMENTS

MHD fields from a global three-dimensional simulation of the great Mar ch 24, 1991, storm sudden commencement (SSC) are used to follow the tr ajectories of particles in a guiding center test particle simulation o f radiation belt formation during this event. Modeling of less intense events during the Lifetime of the CRRES satellite, with similar morph ology but less radial transport and energization, is also presented. I n all cases analyzed, a solar proton event was followed by an SSC, lea ding to the formation of a new proton belt earthward of solar proton p enetration. The effect on particle energization of varying solar wind and model pulse parameters is investigated. Both a seed population of solar protons and the SSC shock-induced compression of the magnetosphe re are necessary conditions for the formation of a new proton belt. Th e outer boundary of the inner zone protons can be affected by an SSC a nd a newly formed belt can be affected by the ensuing or a subsequent storm, which may occur in rapid succession, as was the case in June an d July 1991. The acceleration process is effective for both northward and southward IMF, with more energization and inward radial transport for the southward case for otherwise comparable solar wind parameters, because of the initially more compressed magnetopause in the southwar d case. The inner boundary and stability of the newly formed belt depe nds on the magnitude of radial transport at the time of formation;and subsequent ring current perturbation of adiabatic trapping.