The 10-rotation Periodicity in Sunspot Areas

TL;DR

This study identifies a 10-rotation periodicity in sunspot area fluctuations, mainly during high solar activity periods, using auto-correlation and wavelet analyses across 12 solar cycles, considering hemispheric asymmetries.

Contribution

It reveals the presence and activity-dependent nature of a 10-rotation periodicity in sunspot areas, with separate analysis of hemispheres and fluctuation polarities.

Findings

10-rotation period is prominent during high activity

Period exists during some low activity periods

Hemispheric asymmetry affects periodicity detection

Abstract

I study the sunspot area fluctuations over the epoch of 12 solar cycles (12-23). Lately, I found three significant quasi-periodicities at 10, 17 and 23 solar rotations, but two longer periods could be treated as subharmonics of the 10-rotation period. Thus, I search this period during the low- and the high-activity periods of each solar cycles. Because of the N-S asymmetry I consider each solar hemisphere separately. The skewness of each fluctuation probability distribution suggests that the positive and the negative fluctuations could be are examined separately. To avoid the problem when a few strong fluctuations could create an auto-correlation or a wavelet peak, I also analyse the transformations of fluctuations for which the amplitudes at the high- and the low-activity periods are almost the same. The auto-correlation and the wavelet analyses show that the 10-rotation period is mainly detected during the high-activity periods, but it also exists during a few low-activity periods.