Studies of modern and ancient solar energetic particles

Abstract

Modern solar energetic particles (SEPs) have been studied for about 50 years by satellites and groundbased observations. These measurements indicate much about the nature of SEPs but cover too short a period to quantify the probabilities of very large solar particle events. Many SEPs have high enough energies to make nuclides in material in which they interact. Radionuclides measured in lunar samples have been used to extend the record about SEPs back several million years. Some new measurements of modern SEPs during the last solar cycle and new results for nuclides made by SEPs in lunar samples are presented and their implications discussed. Both the modern and ancient records need to be improved, and methods to get a better understanding of solar energetic particles discussed. The fluxes of SEPs during the last million years show an increasing trend when averaged over shorter radionuclide half-lives.