Radial dependence of solar energetic particle events

Abstract

Solar energetic particle (SEP) events have been observed from Mercury's orbit to beyond Saturn's. With increasing radial distance, the number of particle events decreases, maximum fluxes decrease, time scales increase and profiles become more rounded. Relevant observations from Helios and Ulysses will be reviewed; focus is on anisotropies, time scales, streaming-limits and invariant spectra. Implications for the current paradigm of SEP events will be discussed and SEP history will be addressed: SEP events, in particular at larger distances, cannot be regarded as isolated events but are modified by previous SEP events and other aspects of solar activity.