Simulation Results for Heavy Ion Spectral Variability in Large Gradual Solar Energetic Particle Events

Abstract

Large gradual solar energetic particle (SEP) events have been found to be highly variable in their heavy ion characteristics at high energies, where these events start to show signatures typically associated with impulsive events. The signatures include enhancements in heavy ion abundances, elevated charge states of Fe at high energies, and enhanced 3He/ 4He ratios. We present results from test-particle simulations, considering the behavior of Fe and O ions in a semirealistic model for the solar corona, that diffusive shock acceleration can produce most of the observed features if the seed ions consist of suprathermals from the corona and flares. We also compare our results to a recently developed SEP model of Tylka & Lee (2006) and find that the critical assumptions of the model are qualitatively correct and that, despite its simplicity, it may provide a realistic description of the compositional and spectral variability of heavy ions in SEP events.