Shock Acceleration and Heavy ion Spectral Variability in Large SEP Events

Details Shock Acceleration and Heavy ion Spectral Variability in Large SEP Events Shock Acceleration and Heavy ion Spectral Variability in Large SEP Events

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh41a0298s&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SH41A-0298

Physics

7513 Coronal Mass Ejections (2101), 7514 Energetic Particles (2114), 7845 Particle Acceleration, 7851 Shock Waves (4455)

Scientific paper

Solar energetic particle (SEP) events can roughly be divided into gradual and impulsive events, when considering measurements in the energy range of a few MeV / nucleon. The gradual events typically have much larger particle intensities and coronal elemental abundances, while impulsive events typically show higher mean ionic charges, enhanced 3He/4He ratio and enhanced heavy ion abundances. However, above energies of a few tens of MeVs / nucleon, large gradual SEP events are highly variable in their heavy ion characteristics and some of the differences between gradual and impulsive events become somewhat blurred. For instance, some gradual events show enhanced Fe/O and 3He/4He ratios and elevated mean Fe charge states -- characteristics which are typically associated with impulsive events. It has been proposed that this variability results from a compound seed population, consisting of suprathermal ions from the solar corona and suprathermal ions from flares, and the evolution of the shock oblique angle, as a coronal mass ejection-driven shock moves outwards from the Sun. We present results from test-particle simulations which confirm that diffusive shock acceleration can produce most of the observed features if the seed population contains ions pre-accelerated at flares. We also discuss the features of the produced energy spectra and phenomena which affect them.

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