Energy dependence of cumulative suprathermal and energetic particle fluence plots

Abstract

Suprathermal and energetic particle flux variability can be statistically characterized in a number of ways. As time histories of flux integrals (cumulative fluences) are relevant both for practical reasons (radiation effects) and for a better understanding of the production and propagation processes, simple quantitative methods are of some interest. Previous studies (e.g. Mewaldt et al., 2001)[1] showed that the character of cumulative fluence plots changed substantially with energy. While at several MeV/nuc a few solar particle events predominate, at much lower energies similar contributions from many separate events of various origins were found. We shall now use a simple parametric method for comparisons, and mention some other possibilities. As in the Kolmogorov hypothesis test, the maximum vertical distance of normalized cumulative plots from the straight line valid for a constant flux will be shown to be useful. Small values of that parameter (called K here for Kolmogorov) indicate variation in many small steps, while large K-values correspond to the dominance of a small number of large events. Below a few MeV/nuc K-parameters will be shown to decrease with decreasing energies. Extrapolations to small energies will be mainly discussed.