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Published 2012 | Published
Book Section - Chapter Open

Evolution of suprathermal seed particle and solar energetic particle abundances


We report on a survey of the composition of solar-wind suprathermal tails and solar energetic particles (SEPs) including data from 1998 to 2010, with a focus on 2007 to 2010. The start of solar cycle 24 included several SEP events that were unusually He-poor. We conclude that these He-poor events are more likely related to Q/M-dependent spectral variations than to seed-particle composition changes. We also find that the quiet-time suprathermal Fe/O ratio during the 2008-2009 solar-minimum was dramatically lower (Fe/O ≤ 0.01) than earlier due in part to very low solar activity, but also suggesting contributions from an oxygen-rich source of suprathermal ions of unknown origin.

Additional Information

© 2012 American Institute of Physics. NASA funded this work under grant NNX10AT75G at JHU/APL, and at Caltech under grants NNX08AI11G, NNX10AE45G, and subcontract SA2715-26309 from UC Berkeley under NASA contract NAS5-03131. We thank Eberhard Möbius and Nathan Schwadron for helpful discussions.

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