The 51-day periodicity in cycle 22

On the basis of analysis of the occurrence rate of major flares (X-ray class greater than or equal to M3.0), we present evidence that the 51-day periodicity was in operation during the interval from May 4, 1991 to November 15, 1992. This periodicity is noted to be two times 25.5 days, which has been proposed as the fundamental period of the Sun.