The 152-day periodicity of the solar flare occurrence rate

Abstract

The occurrence rate of solar flares exhibits a periodicity of about 152 days. This periodicity was discovered from analyses of flares observed with the Solar Maximum Mission (SMM), and confirmed by analysis of flares observed by other observatories. This periodicity was also discovered from the flare rate of solar cycle 20 (1965–75). The cause of the 152-day periodicity still remains a mystery. But answers to the following questions will enhance our understanding of it. (1) Is the periodicity a local or a global phenomenon? (2) Is the periodicity due to the interaction of 'hotspots' rotating at different rates such that they align with one another once every 152-day period? (3) Is the periodicity due to the interaction of rotating features originating from g-mode oscillations? Here we report our analysis of 'major flares' observed with the Hard X-ray Burst Spectrometer (HXRBS) aboard SMM and we conclude that the 152-day periodicity is a global phenomenon, and that the answers to questions (2) and (3) are negative.