Onset study of impulsive solar energetic particle events

Abstract

Impulsive solar energetic particle (SEP) events are associated with impulsive X-ray flares, energetic electrons, and enhanced heavy ion abundances. Using instruments on ACE, we have examined the composition and origin of twelve impulsive SEP events from November 1997 to June 2000. have enhanced ‘HerHe ratios compared with the solar wind values. All selected impulsive SEP events The range of ‘HetHe ratios varies from 0.01 to 7.8. By assuming scatter-free propagation at zero degree pitch-angle, we fitted the minimum particle path lengths (from 1.2 to 1.4 AU, as expected), and estimated the ion event release time back at the Sun to within better than 30 minutes in most cases. We found only four events in which the release times agree for both 38-50 keV electrons and ~1 MeVlnucleon ions. Five of our events have significant differences (>40 minutes) between the electron and ion onset times, all with ions injected later. Three impulsive ion events have no association with any impulsive electron event. Seven events have associated solar electromagnetic signatures (Type III radio bursts and/or X-ray flares).