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

TL;DR

This study analyzes the decay behavior of over 750 sunspot groups and their parts, revealing linear dependencies on maximum areas, cyclical variations, hemispheric differences, and latitudinal trends, based on extensive observational data.

Contribution

It provides a detailed analysis of sunspot group decay rates, including internal parts and hemispheric differences, using large datasets, which advances understanding of sunspot decay dynamics.

Findings

Decay rates depend linearly on maximum areas.

Decay rates vary with the solar cycle, especially during the Gnevyshev gap.

Higher decay rates are observed in the northern hemisphere.

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 \citet{2020ApJ...892..107M} 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 SoHO Debrecen Sunspot Database (SDD ) and the Greenwich Photoheliographic Results (GPR) as well as the Debrecen Photoheliographic Data (DPD). 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 30-50 MSH/day for the sunspot groups and penumbrae and 5-10 MSH/day 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 of the decay rates in the activity range toward higher latitudes.