Mev and Sub-MeV Ion Flux Distributions at 1 AU

MeV and sub-MeV ions (mainly protons) belong to the most variable populations in the inner heliosphere. Distinct events can not be easily defined for low-flux periods, when ‘backgrounds’ of various origin may cover genuine fluctuations. Effects of instrumental noise and particle misidentification and of Poissonian statistics may distort the low-flux side. The fluence distribution of high-flux 'events' appears to be reasonably well approximated by a log-normal model, at least at relatively high energies, while the probability of high daily and hourly mean fluxes decreases faster than predicted by that model. Mainly IMP-8 data are used for the characterization of flux distributions at low and high solar activity periods of the last three solar cycles.