A Model for Spectral and Compositional Variability at High Energies in Large, Gradual Solar Particle Events

Details A Model for Spectral and Compositional Variability at High Energies in Large, Gradual Solar Particle Events A Model for Spectral and Compositional Variability at High Energies in Large, Gradual Solar Particle Events

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh23c..05t&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH23C-05

Physics

2114 Energetic Particles (7514), 7513 Coronal Mass Ejections (2101), 7514 Energetic Particles (2114), 7519 Flares

Scientific paper

Shocks driven by fast coronal mass ejections (CMEs) are generally believed to be the dominant accelerators in large, gradual solar energetic particle (SEP) events. A key challenge for this notion has been the highly variable spectral and compositional characteristics of these events above a few tens of MeV per nucleon. We have recently proposed that this variability results from the interplay of two factors: evolution in the shock- normal angle as the shock moves outward from the Sun; and a compound seed population, typically comprising at least suprathermals from the corona (or solar wind) and suprathermals from flares. We present a simple analytical implementation of these ideas (Tylka &Lee, ApJ, 646, 1319, 2006). Our calculations semi-quantitatively reproduce key features of the observed variability, including spectral morphologies and energy dependence in Fe/O, 3He/4He, and mean ionic charges, in ways that are consistent with correlations in the data. The model makes a prediction for the average high-energy Fe/O enhancement that is borne out by thirty years of observations; the model also provides a quantitative explanation for the Breneman &Stone [1985] fractionation effect, a fundamental but previously-unexplained aspect of SEP phenomenology. Our calculations must be bolstered by future efforts incorporating realistic CME-shock simulations and a rigorous treatment of particle transport. Suprathermal densities in the corona and details of the injection process at shocks of arbitrary obliquity also require further investigation. Nevertheless, these first results suggest a comprehensive framework for understanding the complexity of high-energy variability in terms of shock physics for most, if not all, large SEP events. Supported by the Office of Naval Research and NASA's Living With a Star Targeted Research and Technology Program under DPR NNH05AB581.

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