Wiedenbeck

Observations of ³He-Rich Solar Energetic Particle Events with the Solar Isotope Spectrometer on ACE

E. R. Christian¹, C. M. S. Cohen², A. C. Cummings², R. A. Leske², R. A. Mewaldt², P. L. Slocum³, E. C. Stone², T. T. von Rosenvinge¹, M. E. Wiedenbeck³

1 NASA / Goddard Space Flight Center, Greenbelt, MD 20771

2 California Institute of Technology, Pasadena, CA 91125

3 Jet Propulsion Laboratory, Pasadena, CA 91009

During the first 20 months of operation of the Advanced Composition Explorer (ACE), the Solar Isotope Spectrometer (SIS) measured significant enhancements of the ³He/⁴He ratio at 4-5 MeV/nucleon on more than 60 days. The ratio ranged from a maximum somewhat greater than unity down to an instrumental limit of a few percent at these energies. Using this data set we have undertaken a systematic survey of the characteristics of ³He-rich solar energetic particle events. We will discuss the SIS observations of ³He and ⁴He isotopic abundances, intensities, spectral hardness, timing characteristics, and heavy element content. Where possible, we will also examine correlations with data from other sources for the same events, including particle measurements made at lower energies and observations of electromagnetic radiations from the flare site.