Abundance Variations of Energetic He+ at 1AU: ACE/SEPICA Observations

Details Abundance Variations of Energetic He+ at 1AU: ACE/SEPICA Observations Abundance Variations of Energetic He+ at 1AU: ACE/SEPICA Observations

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusmsh22c..08k&link_type=abstract

American Geophysical Union, Spring Meeting 2002, abstract #SH22C-08

Physics

2109 Discontinuities, 2118 Energetic Particles, Solar, 2139 Interplanetary Shocks, 2152 Pickup Ions, 2164 Solar Wind Plasma

Scientific paper

We have investigated Solar Energetic Particle (SEP) events with unusually high abundance in He+ that have been observed between 1998 and 2000 with ACE/SEPICA. The typical He+/He2+ abundance ratio in the solar wind/corona is of the order of 10e-4. During SEP events the He+/He2+ ratio can be closer to one. We have determined an average abundance ratio of the high energetic population over one year to be of the order of 0.1. Possible sources for this substantially enhanced He+ are interstellar pickup ions or solar ejecta (CMEs). We have investigated the temporal evolution and the energy spectra of these events in detail. Usually the increase of the He+/He2+ abundance ratio coincides with the arrival of the shock (either driven by a CME or associated with a CIR) or a discontinuity. This seems to suggest local acceleration of these ions. The investigations show that interstellar pickup ions are the source for the He+ enhancement because it does not seem to be associated with ejecta material. A comparison with SOHO/CELIAS/STOF observations shows that the He+/He2+ ratio appears to be consistently lower at higher energies, and the observed temporal variability decreases with increasing energy. We have identified the type of discontinuities which are associated with an increase of the He+/He2+ ratio, and we will discuss the implications for the acceleration of He+ pickup ions.

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