Energetic Particle Composition at 1 AU Between Large Gradual SEP Events
Abstract
Measurements of solar energetic particles (SEPs) from large gradual SEP events in Cycle 23 have suggested that there may be qualitative differences in processes which affect SEP fractionation over the course of the Cycle. It is not known whether there are similar variations in SEP fractionation between the large gradual events. Using data from the Solar Isotope Spectrometer on the Advanced Composition Explorer, we have examined the heavy element (Z>=6) composition of energetic particles at 1 AU during times with low--to--moderate solar activity between February 1998 and February 2002. These time periods have included groups of many consecutive days between the large gradual SEP events, as well as shorter time periods in which small SEP events occurred. We have measured the abundances of heavy elements over the range ~8--20~MeV/nucleon. As a comparison, we have investigated the heavy element content of an additional set of similar small SEP events from January 1994 through December 1995, using data in the energy ranges ~0.5--10 and ~10--40~MeV/nucleon data from the LICA and HILT instruments on the Solar Anomalous and Magnetospheric Particle Explorer. In each of these data sets, we have searched for compositional signatures which are similar to those found in large gradual SEP events occurring during the same time periods. We discuss the implications of these measurements for the nature of SEP events during the rising and declining phases of Solar Cycle 23. This research was supported by NASA at The Aerospace Corporation, the University of Maryland, Caltech, JPL, and GSFC.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSMSH42B..03S
- Keywords:
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- 7514 Energetic particles (2114);
- 7536 Solar activity cycle (2162);
- 2114 Energetic particles;
- heliospheric (7514);
- 2162 Solar cycle variations (7536)