The mid-term periodicities in sunspot areas
Abstract The sunspot area fluctuations for the northern and the southern hemispheres of the Sun over the epoch of 12 cycles (12–23) are investigated. Because of the asymmetry of their probability distributions, the positive and the negative fluctuations are considered separately. The auto-correlation analysis of them shows three quasi-periodicities at 10, 17 and 23 solar rotations. The wavelets gives the 10-rotation quasi-periodicity. For the original and the negative fluctuations the correlation coefficient between the wavelet and the auto-correlation results is about 0.9 for 90% of the auto-correlation peaks. For the positive fluctuations it is also 0.9 for 70% of the peaks. For 90% of cycles in both hemispheres the auto-correlation analysis of negative fluctuations shows that two longer periods can be represented as the multiple of the shortest period. For positive fluctuations such dependences are found for more than 50% of cases.