Measurements of cosmogenic isotopes with different life times in lunar and meteoritic rocks allow one to make rough estimates of the SEP flux over different timescales. The directly space-borne-measured SEP flux for past decades is broadly consistent with estimates on longer timescales – up to millions of years.
Measurements of nitrates in polar ice make it possible to reconstruct strong SEP events for nearly the past five centuries.
An analysis of various kinds of data suggests that the distribution of the intensity of SEP events has taken a break, and the occurrence of extra-strong events (with the F30 fluence exceeding 1012) is unlikely.
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