A Revised Classification Scheme for Solar Energetic Particle Events
AIR FORCE RESEARCH LAB HANSCOM AFB MA SPACE VEHICLES DIRECTORATE
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We propose a revision of the standard impulsivegradual classification scheme for solar energetic particle SEP events. In the new scheme, SEP events are divided into two basic classes Flare and Shock. The flare class corresponds to the old impulsive class, or more specifically, the 3He-rich subset of that class. The shock class, which replaces the gradual class, consists of two subclasses based on shock geometry and seed particle population, either quasi-perpendicular operating on flare particle seeds or quasi-parallel coronal or solar wind suprathermals. Our revision was motivated by recent observations of large and presumably gradual events that had impulsive event composition and charge states at high energies. The new classification scheme is based on the Tylka et al. 2005 study linking shock geometry and seed populations to FeO variation in large SEP events. We show that flare time scale, the organizing parameter in the current two-class picture, can be incorporated naturally into the revised SEP classification scheme, and we review recent evidence that supports the proposed framework.