On the Decay of Sunspot Groups and Their Internal Parts in Detail

Abstract

Abstract The decay of sunspot groups is a relatively unknown field since most studies have focused mainly on the decay of sunspots or sunspot groups, but only on small samples. As an extension of the recent work of Muraközy (2020), which is based on a large verified sample, this study investigates not only the long-term behavior of the decay of sunspot groups but also the dynamics of their parts. The aim of the present work is to search for dependencies of the decay process in order to find physical conditions that modify or contribute to the decay. The investigations are based on the catalog of the SoHO Debrecen Sunspot Database (SDD) and the Greenwich Photoheliographic Results as well as the Debrecen Photoheliographic Data. Altogether more than 750 sunspot groups were considered. The decay rates have been calculated for the total, umbral, and penumbral area of the groups and in the case of the SDD’s groups they have been calculated for both the leading and the following parts. The decay rates depend linearly on the maximum areas and ranged from 30 to 50 millionths of the solar hemisphere (MSH) day−1 for the sunspot groups and penumbrae and 5–10 MSH day−1 for the umbrae throughout the cycle. The decay rates fall significantly during the Gnevyshev gap and show 4 + 4 Schwabe cyclical variations in the ascending/descending phases, but it is always higher in the northern hemisphere. There is a slight decrease in the decay rates in the activity range toward higher latitudes.