Assessment of a planetary model to predict Rieger periodicity in sunspots and flares

Abstract

This paper develops a planetary model to predict the occurrence of intermediate range periodicity in solar activity, in particular the ~155 day Rieger periodicity in flare activity. It is shown that periodicity at half integer multiples of the period of Mercury occurs consistently in indices of solar activity. For this reason the planetary model is based on the triggering of sunspot emergence when planetary tides peak at times of conjunction of Mercury with Venus, Earth and/or Jupiter. The periodicity of components in the planetary model match reasonably well the observed intermediate periodicity in sunspot and flare activity with the strongest model component occurring at 155 day period. A comparison of filtered versions of the model and the N.O.A.A. flare index at 155 day periodicity demonstrates the potential for both short term, (within a solar cycle), and longer term, (over several solar cycles), predictive capability of the model. However, this assessment finds that prediction of 155 day periodicity in flare activity is effective only when the north and south hemispheric components of flare activity are in-phase.