The Ion Composition In Solar Energetic Particle Events Observed In 1993-1995

Five large events of solar energetic particles (SEP) during three years from 1993 to 1995 have been observed by high energy particle (HEP) instruments onboard GEOTAIL spacecraft. The composition of energetic ions, their energy spectra and time profiles of ion intensity were measured for the SEP events. Three SEP events observed on Feb. 15, 1993, Mar. 4, 1993 and Oct. 20, 1994, are enriched in Fe ions (> 10 MeV/n). The enhancement of Fe ions was observed at the onset time of SEP events (Mar. 4, 1993 and Oct. 20, 1994). The onset of the SEP events seems to have a feature with "impulsive" and "gradual" characteristics. This indicates a mixture of different seed populations and acceleration processes operating in these events.