Importance of Magnetically Complex Active Regions on Solar Flare Occurence

Daily numbers of solar H® flares from 1955 to 1997 and daily numbers of magnetically classified active regions for the time span 1964 1997 are studied applying wavelet power spectra. The occurrence of dominant periods in the range of ~24 days (synodic) is investigated considering the northern and southern hemisphere separately. From the flare events it is revealed that the 24-day period occurs in each of the four solar cycles investigated (no. 19 22). The 24-day period can be established also in the occurrence rate of subflares but occurs more prominently in major flares (importance classes >1). Magnetically complex active regions, i.e. including a gamma and/or delta configuration, show the 24-day period closely related to those found for major H alpha flares, whereas it cannot be established for non-complex alpha, beta groups.