Variation in solar energetic particle elemental composition observed by ACE and Wind

We have used ACE and Wind data to study C/O and Fe/O ratios at ∼2.6-15 MeV/nuc in nine large solar energetic particle (SEP) events between November 1997 and November 1998. Six events have event-integrated Fe/O ratios that are larger than the nominal coronal value by a factor of two or more. However, the energetic storm particle event of 25 August 1998 single-handedly restores the fluence-weighted Fe/O average to nearly the coronal value. We suggest that this balancing indicates a common acceleration mechanism in all of these events. We also compare SEP results to a recent ∼300-day survey of slow solar wind by Ulysses. The average solar-wind C/O ratio is significantly larger (by ∼40%) than in SEPs and in the photosphere. The origin of this difference in C/O is not understood. Finally, we also use 1-hour and 2-hour averaged data to examine intra-event correlations of SEP Fe/O vs. C/O