Variation of sunspot groups' polarity separation during their evolution

Abstract

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 during the decay phase. The aim of the present work is to study the separation distance variations during the active region evolution on a large statistical sample. Altogether more than 2000 individual sunspot groups were taken into account. The investigation is mainly based on data of the SoHO/MDI - Debrecen Sunspot Data (SDD) catalog which covers the time span 1996-2010, practically the whole solar cycle 23. For check of the possible cyclical variation the Debrecen Photoheliographic Data (DPD) is used which contains data for solar cycles 20-24. The separation distance is calculated between the leading and following centers of mass and 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 medium size groups, but continues its increase 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, i. e., the larger the sunspot group the greater its extent. Cycle and cycle phase dependencies as well as hemispheric connection can also be observed.