Solar Energetic Particles

Some observational aspects of solar energetic particles (SEPs) are briefly discussed. The shift from the flare paradigm of SEP origin through the two-class paradigm of impulsive and gradual SEP events to hybrid events is described. Comprehensive investigations of coronal mass ejections (CMEs) and solar energetic particles during the SOHO era have shown that there is a good correlation between the occurrence of large SEP events and fast and wide CMEs. Shocks driven by these CMEs in the solar corona and interplanetary space accelerate the solar wind suprathermal particles. Observations of ionic charge states and elemental composition of high-energy solar particles indicate that also flare material is present in the seed populations of large gradual SEP events. Whether this material is remnant from previous flares and accelerated by CME-driven shocks or is directly accelerated in the flare processes, is still under vigorous research. Significant progress is expected from future solar missions reaching close to the sun and leading to better understanding of the processes in the inner heliosphere.