The Ten-Rotation Quasi-periodicity in Sunspot Areas

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.

The solar magnetic activity band interaction and instabilities that shape quasi-periodic variability

“…The slight offset between peaks in the low- (28 days) and high-latitude (30 days) period is consistent with observed solar differential rotation 24 . The broad peak centred around 330 days is common to the timeseries, although the southern hemisphere seems to be shifted further and is consistent with the analysis of Getko 25 26 . This appears to be the primary (quasi-)periodicity of the magnetic surges that shape the heliosphere and drive the host of energetic phenomena observed as described above.…”

“…Figure 7 permits a phenomenological explanation of the quasi-periodicities (of order 150 days) that have been observed in a large number of heliospheric quantities by Rieger and others 9 10 11 25 26 27 28 29 35 . Those are ‘hybrid' periodicities—a consequence of the phase relationship between the short-term variability in each solar hemisphere.…”

Quasiperiodic Variations of Coronal Mass Ejections with Different Angular Widths

“…Getko (2008) found that the sunspot area fluctuations in the northern and the southern hemispheres show quasiperiodicity over 9 months. Moreover, the result of Getko (2014) reported that this period is mainly detected during the high-activity periods, which is the same as our results for the local wavelet spectra. It may reveal the special characteristics of partial-halo CMEs compared to other angular widths.…”