Solar Flare Cycles

We present a review of different solar flare periodicity intervals. Our analysis includes a statistical investigation of flare occurrence and N-S hemispheric distribution over the last three 11-yr solar cycles (SCs 21-23, corresponding to the period 1976-2001). Moreover, we try to estimate if there is any connection between the flare activity and the strength of solar cycles. For that purpose, we studied not only the number of flares occurring monthly and annually, but we also used two indices that estimate the energy emitted by flares registered in the optical Hα line, as well as in the soft X-ray 1-8 Å band. The strange behaviour of SC 22 descending phase, with short but intense increments in flare activity, having a high degree of N-S asymmetry, could be the cause of the "abnormal" appearance of SC 23. The new magnetic dipole begins to lose part of its energy even during the descending phase of SC 22, so that the activity of SC 23 proves to be below the predicted values.