The ion composition in solar energetic particle events observed in 1993-1995

Five large events of solar energetic particles (SEP) during three years fro m 1993 to 1995 have been observed by high energy particle (HEP) instruments onboard GEOTAIL spacecraft. The composition of energetic ions, their energ y spectra and time profiles of ion intensity were measured for the SEP even ts. Three SEP events observed on Feb. 15, 1993, Mar. 4, 1993 and Oct. 20, 1 994, are enriched in Fe ions (> 10 MeV/n). The enhancement of Fe ions was o bserved at the onset time of SEP events (Mar. 4, 1993 and Oct. 20, 1994). T he onset of the SEP events seems to have a feature with "impulsive" and "gr adual" characteristics. This indicates a mixture of different seed populati ons and acceleration processes operating in these events.