Energetic particle production in flares

Abstract

Bursts of energetic ions and electrons are frequently seen in interplanetary space and it is beyond doubt that the majority originate at or near the Sun. Many events are correlated with major solar flares and it is customary to associate such flares with energetic particle production. Possible acceleration mechanisms are presented, and we argue that the particle production occurs following magnetic reconnection relatively high in the corona; the bulk of the energy goes into the ionic, rather than the electronic, component. The principal characteristics of energetic solar particle events are reviewed briefly. In small events only a modest amount of energy is deposited below the transition zone, thereby producing a minimal Hα response. In large events, as the bulk of the energy is carried by protons of less than 1 MeV, only during the impulsive phase is a significant amount of energy deposited below the transition zone. Later in the event, chromospheric ablation enhances the coronal density, inhibiting further energy deposition in the chromosphere. A model is outlined whereby acceleration of the electrons responsible for the impulsive hard X-ray burst occurs in the chromosphere as a result of the interaction of the primary ions. Observations supporting this hypothesis are discussed.