The Occurrence Rate of 3He-rich Solar Energetic Particle Events at Solar Minimum

Details The Occurrence Rate of 3He-rich Solar Energetic Particle Events at Solar Minimum The Occurrence Rate of 3He-rich Solar Energetic Particle Events at Solar Minimum

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh14a..05w&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH14A-05

Astronomy and Astrophysics

Astrophysics

[2114] Interplanetary Physics / Energetic Particles, [7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7536] Solar Physics, Astrophysics, And Astronomy / Solar Activity Cycle

Scientific paper

Flare-associated solar energetic particle (SEP) events, recognized by their characteristic enhancement of 3He/4He, are very common at solar maximum. Reames (1999) reported the occurrence rate as ~100/year as seen by a single spacecraft at 1 AU, and inferred a rate ~1000/yr over the visible disk of the Sun after correcting for the finite longitudinal spread of these events. At solar minimum the rate is distinctly lower, but lack of adequate coverage by instruments capable of measuring these events has prevented an accurate determination of the solar minimum rate. The two STEREO spacecraft, launched in late 2006, have accumulated nearly 3 years of data during the quietest solar minimum since the beginning of the space age. Low Energy Telescopes (LETs) measure He isotopes above ~2 MeV/nuc from the two STEREO locations with large geometrical factor (4 cm2sr) and nearly 100% data coverage. We have surveyed the STEREO/LET data set to derive the occurrence rate of 3He-rich SEP events at solar minimum. We have also extended our previous ACE study of the fraction of time that 3He is present near 1 AU (Wiedenbeck et al. 2003, 2005) so that it now covers 1997-2009 and clearly shows the magnitude of the change between solar maximum and solar minimum. We will report results from both of these studies and compare with the limited information that is available from previous solar minima. This work was supported by NASA at JPL, Caltech, GSFC, and APL.

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