Significant solar proton events for five solar cycles (1954-2007)

Abstract

Using a solar proton database for the past five solar cycles (1954-2007) we have determined the total solar proton fluence above 10 MeV and the number of discrete events that occurred each cycle. We find: (1) The number of discrete events in cycles 19-22 were essentially the same; (2) Cycles 20 and 21, at the beginning of the space era, were relatively benign with respect to solar proton fluence; (3) Approximately 16% of the total number of discrete events each cycle are relativistic solar cosmic ray events (i.e. GLEs); (4) Cycle 23 has been the most active cycle since 1954. We also find that the number of GLEs can be associated with a relatively small number of solar active regions with each region producing several large events in a sequence of activity. Of the 70 GLEs between 1942 and 2006, 36 of these events were associated with only 15 active solar regions.