Acceleration and storage of energetic particles in the solar corona

Abstract

Observations of solar energetic particles (SEP) in interplanetary space have considerably advanced our understanding of particle acceleration near the Sun in recent years. Based on particle abundances, ionisation states, time evolution and longitude distributions, two distinct classes of SEP events have been identified. They are usually described as “impulsive” and “gradual”, with reference to the time scale of the accompanying soft x-ray flare. It is now widely accepted that these classes carry the signature of different acceleration processes: impulsive heating in the flare process and shock acceleration, respectively. It is argued that coronal particle transport in large events (gradual events) can be understood in terms of shock propagation and acceleration eliminating the ad hoc concept of coronal diffusion. Finally, new results of solar flare gamma-ray emission at high energies are discussed which shed new light on particle storage and acceleration in the solar corona.