CONFIRMATION OF THE 25.5-DAY FUNDAMENTAL PERIOD OF THE SUN USING THE NORTH-SOUTH ASYMMETRY OF THE FLARE INDEX

Short-term periodicities of solar activity were studied. To perform th e study, a north-south asymmetry time series was constructed by using the northern and the southern hemisphere flare index values for solar cycle 22. The statistical significance of this time series was calcula ted. It indicates that in most of cases the asymmetry is highly signif icant during cycle 22. Power spectral analysis of this time series rev eals a periodicity around 25.5 days, which was announced before as a f undamental period of solar activity (Bai and Sturrock, 1991). To inves tigate the time agreement between the two hemispheres, the phase distr ibution was studied and a phase shift of about 0.5 was found. An activ ity trend from the north to the south was found.