Confirmation of a 152 day periodicity in the occurrence of solar flares inferred from microwave data

Abstract

Evidence for a periodicity of about 155 ± 5 days in the production of energetic solar flares ws reported in 1984 by Reiger et al. and Kiplinger et al. The data on which these analyses were based are restricted to the years 1980 through early 1984. To see whther this periodicity is a persistent phenomenon, we have examined the occurrences of flares inferred from microwave data, which are available for most of the present and previous solar cycles. We find strong confirmation of a 152 day periodicty in the time interval previously studied, demonstrating that thee flares are a useful indicator for the observed periodicity. We find evidence for persistence of the periodicity in the previous cycle (cycle 20). In cycle 20 the periodic modulation of the flare occurrence rate was weaker than in cycle 21, but the phase has apparently remained coherent through both cycles.