The Near 160 Day Periodicity in the Photospheric Magnetic Flux

A periodicity near 154 days was discovered in the number of high-energy solar flares detected by Solar Maximum Mission (SMM) and Geosynchronous Operational Environmental Satellites (GOES) during the time interval 1980-1984 (Rieger et al.; Dennis). In this paper, we analyze the historical records of photospheric magnetic flux to show that during solar cycle 21 the periodicity appeared in the photospheric magnetic flux linked to strong magnetic fields, 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 flares are triggered in regions of enhanced magnetic complexity (Kurokawa Ishii et al.), we propose that the appearance of the periodicity in the magnetic flux materializes through the formation of new sunspots within already formed sunspot groups, setting up a suitable scenario for the occurrence of energetic flares. This scenario leads to the occurrence of periodic episodes of magnetic reconnection between old and new emergent magnetic flux, able to trigger the periodic occurrence of energetic flares recorded by SMM and GOES.