THE 77-DAY PERIODICITY IN THE FLARE RATE OF CYCLE-22

The occurrence times of major flares of solar cycle 22 are analyzed to detect periodicities. We find that a periodicity of 77 days was in operation in the 15 month interval from 1988 November to 1990 February for six cycles. During the rest of 1990 no periodicity was discernible; however, it seems that the 77 day periodicity has resumed in 1991. This 77 day period is interpreted as the third subharmonic of the fundamental period of approximately 25.d5. In this interpretation, the 154 day periodicity is the sixth subharmonic. We also find that when the 77 day periodicity or the 154 day periodicity is in operation the occurrence rate of major flares is much higher than is expected from the relative sunspot number.