Return of the Near 160 Day Periodicity in the Photospheric Magnetic Flux during Solar Cycle 23

Abstract

A periodicity between 152 and 158 days was discovered in the daily number of high-energy solar flares detected by the Solar Maximum Mission (SMM) and the Geosynchronous Operational Environmental Satellites (GOES) around the maximum of solar cycle 21. In a previous work we pointed out that this periodicity had been time-coincident with a periodic emergence of magnetic flux in the form of strong magnetic fields, which suggested a causal relationship between both periodicities. Using the Mount Wilson Sunspot Index, evidence is presented for the return of the periodicity in the strong photospheric magnetic flux during the current solar cycle. The periodicity has reappeared around the solar activity maximum with a frequency similar to that of solar cycle 21, but contrary to what happened during cycle 21, it is completely absent in energetic flares. A tentative explanation for this feature is that in the current solar cycle, part of the periodic emergence of magnetic flux has taken place away from already developed sunspot groups and so has not contributed to enhance their magnetic complexity, which has prevented the triggering of periodic energetic flares.