Solar energetic particles and coronal mass ejections: A perspective

Energetic charged particles are ubiquitous in space, and are apparently present wherever the ambient gas density is low enough. Solar energetic particles were first observed in the 1940’s and have been the subject of intense study ever since. The essential similarity of their spectral slopes from event to event and with those observed in many different astrophysical sites places significant general constraints on the mechanisms for their acceleration and transport. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in broadband turbulence, can account naturally for the very similar specta. It is suggested that acceleration of solar energetic particles, both the CME-associated gradual events and the impulsive events are accelerated mostly by shocks. ³He-rich events may be the exception, although selection during the injection process may cause the enhancement of ³He.