Variation in the polarity separation of sunspot groups throughout their evolution

During the emergence of sunspot groups, the footpoints of their leading and following parts move apart. This diverging motion results in the stretching of the active regions, which continues throughout the decay phase. The aim of the present work is to study the separation distance variations throughout the active region evolution on a large statistical sample. Altogether, we took more than 2000 individual sunspot groups into account. Our investigation is mainly based on data of the SoHO/MDI-Debrecen Sunspot Data (SDD) catalog, which covers the years 1996-2010, specifically, nearly the whole of solar cycle 23. For our check of the possible cyclical variation, we used Debrecen Photoheliographic Data (DPD), which contains data for solar cycles 20-24. The separation distance was calculated between the leading and following centers of mass, revealing that it starts to increase after the emergence and shows a plateau around the peak flux. The polarity separation reaches its maximum in the decay phase and then starts to decrease in the cases of the largest and midsize groups, but it does continue its rise in the case of the smallest groups. This decrease is caused by the eastward motion of the leading part, while the following part continues its backward motion. The separation distance is size-dependent, that is, the larger the sunspot group, the greater its extent. The cycles and cycle phase dependencies as well as related hemispheric connections have also been observed.