Abundances of Helium Isotopes at MeV Energies in the SEP Events of Solar Cycle 23

Details Abundances of Helium Isotopes at MeV Energies in the SEP Events of Solar Cycle 23 Abundances of Helium Isotopes at MeV Energies in the SEP Events of Solar Cycle 23

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh43b1516w&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH43B-1516

Other

2114 Energetic Particles (7514), 7514 Energetic Particles (2114), 7984 Space Radiation Environment

Scientific paper

The isotopic composition of the element helium is an important indicator of the origin of solar energetic particles (SEPs) observed in the interplanetary medium, with enhanced 3He/ 4He ratios indicating of the presence of flare-accelerated material. In large gradual events, where CME-driven shocks in the corona and interplanetary medium are predominantly responsible for the particle acceleration, a fraction of the seed material could come either from suprathermals energized in preceding flare events or possibly from the flare event associated with the CME. In impulsive events, which tend to be much less intense, the energetic particles may all be flare accelerated. Between these two extremes are numerous medium-sized events that have received relatively-little attention to date. Using the Solar Isotope Spectrometer (SIS) instrument on the Advanced Composition Explorer (ACE) spacecraft we have measured helium isotopes above 5 MeV/nucleon in hundreds of SEP events observed during the maximum of solar cycle 23. We present an extensive compilation of high energy helium isotope measurements covering the 9 years from the launch of ACE in 1997 through mid-2006 as a database that can aid in understanding the origin of the solar energetic particles observed during this time period. For those SEP events having intensities of heavy elements high enough to be measuremed with SIS, we also compare the helium results with other indicators of flare material such as the Fe/O ratio. This work was supported by NASA at Caltech (under grant NAG5-12929), JPL, and GSFC.

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