Periodical patterns in major flare occurrence and their relation to magnetically complex active regions

Abstract A periodical occurrence rate of major solar flares (observed in hard X-rays) of ∼24 days (synodic) was first reported by Bai (1987) [Bai, T. Distribution of flares on the sun – superactive regions and active zones of 1980–1985. ApJ 314, 795–807, 1987] for the years 1980–1985. Here, we report a significant relation between the appearance of the 24-day period in major Hα flares and magnetically complex sunspot groups (i.e., including a γ and/or δ configuration). From synoptic maps of magnetograms (NSO/KP) patterns in the magnetic flux evolution are traced which might be the cause of the 24-day period observed in flare activity.