Change of rotation rates of sunspot groups during their lifetimes: Clues to the sites of origin of different flux tubes

Abstract

From 103 years of data of non-recurrent sunspot groups and for the two sets (area <100 millionths of hemisphere and >100 millionths of hemisphere), irrespective of their life span, we compute rotation rates and rate of change of rotation rates during their lifetime. It is found that variation of rotation rates of sunspot groups with respect to their lifetime is approximately similar to the radial variation of internal rotation inferred by helioseismology and it is confirmed that all the spot groups decelerate as they evolve into later phases of their lifetime.\ After classification according to different life spans, for the same two data sets, we compute initial rotation rates and rate of change of initial rotation rates of sunspot groups. For the two data sets, variation of initial rotation rates of sunspot groups with respect to their life spans is similar to the radial variation of internal rotation of solar plasma inferred from helioseismology. We also obtain the rate of change of initial rotation rates for two sets of spot groups and the results are as follows: (i) for the area <100, spot groups are accelerated for the life spans of 6-12 days and decelerated for the life spans of 3-6 days; (ii) for the area >100, acceleration for the life spans of 9-12 days and deceleration for the life spans of 3-9 days. Interpreting these results, an attempt is made to locate the sites of origin of spot groups of different sizes and life spans in the convection zone.