Solar proton events during the past three solar cycles

Abstract

More than 200 solar proton events with a flux of over 10 particles/sq cm sec sr above 10 MeV have been recorded at the earth since 1955; at least 15 percent of these events had protons with energies greater than 450 MeV. Although the majority of solar proton events occur in the years around sunspot maximum, these events, including those with relativistic protons, also occur during sunspot minimum. Detector technology has evolved during the last three solar cycles so that a uniform data base does not exist. A count of the number of solar proton events above a specific flux level does not indicate a recognizable trend over the three solar cycles. However, an analysis of the particle fluence in major events indicates that the 19th solar cycle was the most energetic. 63 refs.