Johns Hopkins University Applied Physics Laboratory
Coronal holes, jets, and the origin of 3He-rich solar particle events
Solar energetic particle events with enormous (up to 104) enhancements of the rare isotope 3He were discovered in the 1970s and have remained a puzzle for many years. These are small events, many with no obvious source on the sun. Those that have been associated with other solar activity occur in conjunction with short duration (impulsive) electron events, type III radio emission, and small x-ray flares. A few have been associated with the narrow Coronal Mass Ejections (CMEs). A number of theories have been developed to explain the 3He enrichment by means of preferential heating by resonant plasma waves, but the observations have not allowed any further narrowing of the possibilities. With powerful new instruments on the ACE, SOHO, and Wind spacecraft, together with ground based observations, many new features of these events have been recently discovered. In a recent study (Wang, Pick, and Mason, Astrophys. J., 639, 495-509, March 2006), solar source regions have been identified in a group of 25 3He-rich events, which are typically small flaring active regions lying next to coronal holes containing Earth-directed open field lines. In these regions, emerging magnetic bipoles may be reconnecting with open field lines; since small bipoles emerge continually inside coronal holes, this activity can take place even when no flaring activity is observed. These observations may give evidence of the role of magnetic reconnection both the impulsive and nearly steady state acceleration of ions up to energies of several hundred keV per nucleon.