Cornonal Mass Ejections and Their Role in Solar Energetic Particle Acceleration and Transport

Solar energetic particle (SEP) events have traditionally been classified as either gradual or impulsive. Particles in gradual events are accelerated by shocks driven by large, fast coronal mass ejections (CMEs) and can be observed over a broad range of heliographic longitudes and latitudes, while energetic particles from impulsive solar flares are only detected when the observer is magnetically connected to the flare site. Any CMEs observed in association with impulsive events are typically much smaller than those responsible for gradual events. Observations of SEPs indirectly probe the effects of the transit of CMEs through the inner heliosphere. Timing studies have shown that the highest energy SEPs are accelerated within a few solar radii of the Sun, while at lower energies CME-driven shocks accelerate particles at 1 AU and beyond. Recent studies have shown that a substantial fraction (~10%) of the CME kinetic energy goes into the acceleration of SEPs, making SEPs a significant part of the CME phenomenon. The geometry of the CME, both in terms of the solar longitude of its source and the orientation of its shock relative to the ambient field, plays a critical role in determining the time profiles and possibly the composition of the resulting SEPs. Transport of SEPs can be affected by CMEs, as occasionally an interplanetary CME magnetic loop rooted at the Sun may serve as a conduit for SEPs if a flare injects particles near its footpoint. Recent observational studies relating to SEP acceleration and transport and the role of CMEs in these processes are reviewed, and new observations that will be possible from STEREO and future missions are discussed. This work was supported by NASA under grant NNX08AI11G.