Simulations of radiation belt formation during storm sudden commencements

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Abstract
MHD fields from a global three‐dimensional simulation of the great March 24, 1991, storm sudden commencement (SSC) are used to follow the trajectories of particles in a guiding center test particle simulation of radiation belt formation during this event. Modeling of less intense events during the lifetime of the CRRES satellite, with similar morphology but less radial transport and energization, is also presented. In all cases analyzed, a solar proton event was followed by an SSC, leading to the formation of a new proton belt earthward of solar proton penetration. 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 magnetosphere are necessary conditions for the formation of a new proton belt. The outer boundary of the inner zone protons can be affected by an SSC and 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 and 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 southward case. The inner boundary and stability of the newly formed belt depends on the magnitude of radial transport at the time of formation and subsequent ring current perturbation of adiabatic trapping.