http://arxiv.org/abs/2109.09987
We analyzed the combined 142 years sunspot-group data from Greenwich Photoheliograpic Results (GPR) and Debrecen Photoheliographic Data (DPD) and determined the yearly mean residual rotation rate and the meridional velocity of sunspot groups in different 5-degree latitude intervals. The residual rotation rate is found to be -120 m/s to 80 m/s. In a large number of solar cycles the rotation is to some extent weaker during maxima than that of during minima. There exist alternate bands of equatorward and poleward merdional motions. The equatorward motion is dominant mostly around the maxima of solar cycles with velocity 8-12 m/s, whereas the poleward motion is dominant mostly around the minima but with a relatively weak velocity, only 4-6 m/s. This analysis suggests the existence of equatorward migrating alternate bands of slower and faster than average rotation within the activity belt and no clear equatorward or poleward migrating bands of meridional motions. A statistically significant anticorrelation exists between the meridional motion and residual rotation. The corresponding linear-least-squares best-fit is found to be reasonably good (slope, -0.028 + or – 0.008, is about 3.5 times larger than its standard deviation). The significant negative value of the slope indicates the existence of a strong angular momentum transport toward equator. The slope leads sunspot number (SN) by about 4 and 9 years. The Morlet wavelet spectrum of the slope suggests the existence of approximate 11-year periodicity in the slope almost throughout the data window, but it was very weak during 1920-1940.Overall the results suggest there exits a strong relationship between the slope and amount of activity during a solar cycle. However, no relationship is found between the slope and strength of activity on a long-time scale (longer than 11-year period).
J. Javaraiah
Wed, 22 Sep 21
12/57
Comments: 20 pages, 9 figures, 2 tables, to be published in Solar Physics
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