Solar proton and GLE event frequency: 1955-2000

The number of > 10 MeV solar proton events with peak flux exceeding 10 (cm2 -sec-ster)-1 during each solar cycle was remarkably constant for solar cycles 19-22 even though the total integrated fluence experienced at the earth per solar cycle varied by a factor of four. In addition the number of ground-level events each solar cycle has also remained relatively constant. Similarities between the first five years of this present solar cycle 23 and the first five years of solar cycle 20 are presented. If the proton event occurrence for these two cycles continues to be similar, we would expect the majority of solar proton events to occur during years 5-8 of the 23rd cycle (i.e. from 2000-2004) with perhaps a surge of activity during the waning years of the cycle.