New observations of heavy‐ion‐rich solar particle events from ACE

Following launch of the Advanced Composition Explorer in August 1997, the Solar Isotope Spectrometer measured the composition of nine solar energetic particle events. We have used isotopic measurements of Ne to determine the degree of charge‐to‐mass‐dependent fractionation and infer the charge states of C‐Ni in the four most heavy‐ion‐rich of the nine events. The results indicate a source temperature of ∼4×10 6 K; this and the measured abundances suggest that these four events are more characteristic of impulsive events than gradual. Although the ³He/ 4 He ratios are not enhanced to the level commonly ascribed to impulsive events, there are sizable enhancements over typical solar wind values measured in three of the events.