The Near 160 Day Periodicity in the Photospheric Magnetic Flux

Abstract

A periodicity near 154 days was discovered in the number of high-energy solar Ñares detected by Solar Maximum Mission (SMM) and Geosynchronous Operational Environmental Satellites (GOES) during the time interval 1980È1984 (Rieger et al. ; Dennis). In this paper, we analyze the historical records of photo-spheric magnetic Ñux to show that during solar cycle 21 the periodicity appeared in the photospheric magnetic Ñux linked to strong magnetic Ðelds, while it was absent during solar cycle 22. We also show that there was a time and frequency coincidence between both periodicities during solar cycle 21, which suggests the existence of a causal link between them. Taking into account that high-energy Ñares are triggered in regions of enhanced magnetic complexity (Kurokawa ; Ishii et al.), we propose that the appearance of the periodicity in the magnetic Ñux materializes through the formation of new sunspots within already formed sunspot groups, setting up a suitable scenario for the occurrence of energetic Ñares. This scenario leads to the occurrence of periodic episodes of magnetic reconnection between old and new emergent magnetic Ñux, able to trigger the periodic occurrence of energetic Ñares recorded by SMM and GOES.