Radiation belt formation during storm sudden commencements and loss during main phase

Simulation of the March 24, 1991 storm sudden commencement (SSC) has illuminated the rapid formation of new radiation belts on the particle drift time scale. While this event was the most dramatic in terms of radiation belt effects of the last solar maximum, comparable signatures of such events were seen in 1962 by Explorer 15 and in 1986 by DMSP. Several smaller MeV proton events with comparable particle morphology, but less radial transport and energization, were observed during the lifetime of the CRRES satellite (July 1990 – October 1991), which was well instrumented for both particle and field measurements inside geosynchronous orbit. Typically a solar proton event is accompanied by an SSC in the CRRES data set, while the converse is not always true. An SSC accompanied by solar protons produces a trapped population which remains on closed drift orbits until ring current buildup disrupts trapping, either by violation of the adiabatic trapping criterion or generation of waves whose frequency is comparable to periodic particle motion. Thus, new radiation belts formed around L = 4 by SSC injection are short-lived compared to the March 24, 1991 storm, wherein solar protons were transported radially inward to L = 2.5, with greater energization corresponding to first adiabatic invariant conservation than for the weaker events.