The Ten-Rotation Quasi-periodicity in Sunspot Areas |
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| Authors: | R Getko |
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| Institution: | 1. Astronomical Institute, University of Wroc?aw, Kopernika 11, 51-622, Wroc?aw, Poland
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| Abstract: | 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. |
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