High Energy Ionic Charge State Composition in the October/November 2003 and January 20, 2005 SEP Events

Abstract

The ionic charge states of solar energetic particles (SEPs) probe source-material temperatures and acceleration and transport conditions. The MAST instrument on SAMPEX measures SEP ionic charge states at energies greater than ~15 MeV/nuc and at iron energies up to ~90 MeV/nuc using the geomagnetic filter technique. Charge state measurements for large gradual SEP events by MAST and by other experiments suggest that event-to-event variations in the mean charge states of abundant elements are correlated with abundance ratios (e.g. Fe/O). We present charge state measurements for the October/November 2003 events that suggest different source material temperatures for those events. We also present charge state measurements for the January 20, 2005 event, which contrasts with the previously demonstrated Q(Fe) vs. Fe/O correlation. In this event solar and SEP data indicate that the first high-energy particles left the sun when the shock was ~1.5 solar radii above the solar surface. At this altitude charge-equilibration calculations and the observed mean charge states of +12 for Fe imply that <90 seconds were available to accelerate and release the particles. These observations therefore present a serious challenge to SEP acceleration models.

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