3He-Rich Solar Energetic Particle Events

Abstract

He-rich solar energetic particle (SEP) events show huge enrichments of 3 He and association with kilovolt electrons and Type-III radio bursts. Observations from a new gener- ation of high resolution instruments launched on the Wind, ACE, Yohkoh, SOHO, TRACE, and RHESSI spacecraft have revealed many new properties of these events: the particle en- ergy spectra are found to be either power-law or curved in shape, with the 3 He spectrum often being distinctly different from other species. Ultra-heavy nuclei up to >200 amu are found to be routinely present at average enrichments of >200 times solar-system abun- dances. The high ionization states previously observed near ∼ 1M eV /nucleon have been found to decrease towards normal solar coronal values in these events. The source regions have been identified for many events, and are associated with X-ray jets and EUV flares that are associated with magnetic reconnection sites near active regions. This paper reviews the current experimental picture and theoretical models, with emphasis on the new insights found in the last few years.