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Published 2012 | Published
Book Section - Chapter Open

The dependence of solar energetic particle fluences on suprathermal seed-particle densities

Abstract

Measurements during solar cycle 23 showed that most solar energetic particles (SEPs) are accelerated from a seed-population of suprathermal ions (e.g., >10 keV/nuc) rather than from the bulk solar wind. In this case the SEP fluence should depend on the pre-existing density of suprathermal ions. Lacking near-Sun measurements of suprathermal ion densities we have used ACE/ULEIS daily-average densities of suprathermal Fe at 1 AU during 1998-2005 as a proxy. We find that the maximum Fe daily-average SEP fluences measured by ACE/SIS are apparently limited by the pre-existing suprathermal number density. Similarly, large fluences of Fe in solar energetic particle events only occurred when there was a pre-existing high density of suprathermal Fe. We conclude that in situ suprathermal ion data can play a key role in estimating the probability of large SEP events, or in forecasting all-clear periods.

Additional Information

© 2012 American Institute of Physics. NASA funded this work under grants NNX08AI11G and NNX11A075G at Caltech, and NNX10AT75G at JHU/APL; and subcontracts SA2715-26309 and SA4889-26309 from UC Berkeley under NASA contract NAS5-03131. We are grateful for the availability of SWEPAM data from the ACE Science Center.

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