I apply spectral and auto-correlation analyses to the monthly Wolf number fluctuations for 22 solar cycles and to the group sunspot number fluctuations for 18 solar cycles and find the existence of an 11-month quasi-periodicity in these data. Its strength correlates very well (ρ ≈ 0.8) with the variance of fluctuations. Moreover, for both Wolf and group sunspot indexes I divide a stationary version of fluctuation time series into two parts: those from periods of low and high solar activity. I find statistically significant quasi-periodicity (9 months) in both high-and low-activity data sets. I also find the quasi-period of about 15 months in the time series of high-activity periods.

A new method for the evaluation of strong positive monthly Wolf number fluctuations is presented. The only input it requires is the periodic or quasi-cyclical time series. To evaluate very strong activity complexes within different phases of the 11-year cycle a percentage index of participation of an activity complex in the monthly Wolf number is introduced. I find fair agreement between strong positive Wolf number fluctuations and development curves of large activity complexes.

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.

Sunspot-area fluctuations over an epoch of 12 solar cycles (12 -23) are investigated in detail using wavelets. Getko (Universal Heliophysical Processes, IAU Symp. 257, 169, 2009) found three significant quasi-periodicities at 10, 17, and 23 solar rotations, but two longer periods could be treated as subharmonics of the ten-rotation quasi-periodicity. Therefore we focused the analysis on the occurrence of this quasi-periodicity during the low-and high-activity periods of each solar cycle. Because of the N -S asymmetry, each solar hemisphere was considered separately. The skewness of each fluctuation-probability distribution suggests that the positive and negative fluctuations could be examined separately. To avoid the problem that occurs when a few strong fluctuations create a wavelet peak, we applied fluctuation transformations for which the amplitudes at the high-and the low-activity periods are almost the same. The wavelet analyses show that the ten-rotation quasi-periodicity is mainly detected during the high-activity periods, but it also exists during a few low-activity periods. The division of each solar hemisphere into 30• -wide longitude bins and the wavelet calculations for the areas of sunspot clusters belonging to these 30• bins enable one to detect longitude zones in which the ten-rotation quasi-periodicity exists. These zones are present during the whole high-activity periods and dominate the integrated spectra.

The Zubrzycki method is utilized to find all sunspot groups which are close to each other during each Carrington rotation. The sunspot group areas and their positions for the years 1874-2008 are used. The descending, the ascending and the maximum phases of solar cycles for each solar hemisphere are considered separately. To establish the size of the region D where the clusters are searched, the correlation function dependent on the distance between two groups is applied. The method estimates the weighted area of each cluster. The weights dependent on the correlation function of distances between sunspot groups created each cluster. For each cluster the weighted position is also evaluated. The weights dependent on the areas of sunspot groups created a given cluster. The number distribution of the sunspot groups created each cluster and the cluster statistics within different phases of the 11-year cycle and within all considered solar cycles are also presented.