Size distributions of solar flares and solar energetic particle events

Abstract

We suggest that the flatter size distribution of solar energetic proton (SEP) events relative to that of flare soft X-ray (SXR) events is primarily due to the fact that SEP flares are an energetic subset of all flares. Flares associated with gradual SEP events are characteristically accompanied by fast (≥1000kms-1) coronal mass ejections (CMEs) that drive coronal/interplanetary shock waves. For the 1996-2005 interval, the slopes (α values) of power-law size distributions of the peak 1-8 Å fluxes of SXR flares associated with (a) >10MeV SEP events (with peak fluxes ≥1prcm-2s-1sr-1) and (b) fast CMEs were 1.3-1.4 compared to 1.2 for the peak proton fluxes of >10MeV SEP events and 2 for the peak 1-8 Å fluxes of all SXR flares. The difference of 0.15 between the slopes of the distributions of SEP events and SEP SXR flares is consistent with the observed variation of SEP event peak flux with SXR peak flux. © 2012 The American Astronomical Society. All rights reserved.