The Rotation Rate of the Active Longitude and Sunspot Groups on It and Other Characteristics of Sunspot Groups at the End of the Descending Branch of Solar Cycle 24

Abstract

The longitudinal distribution and characteristic features of sunspot groups during the end of the descending branch of Solar Cycle 24 are analyzed. The main activity turned out to be concentrated in the 60° longitude band, whose position coincided in the northern and southern hemispheres. We obtained a synodic rotation period of the activity zone of 26.6 days, which is shorter than during the corresponding phase of the previous cycles and is probably related to the variation not only in latitude but also in the depth of the active longitude source localization. The groups of sunspots observed in the active longitude zone are characterized by a more compact latitudinal distribution and an increased number of not only large sunspots but also small ones with areas smaller than 50 Msh. Furthermore, the lifetime of small sunspots in this area is longer in contrast to similar sunspots found elsewhere on the solar surface. This indicates a common source of sunspot generation in the active longitude zone. The analysis of the rotation rate of individual sunspot groups with areas larger than 150 Msh in the active longitude zone by the solar disk showed that only a portion of them rotate at a rate close to that of the active longitude zone itself, while another portion rotate at the Carrington rate characteristic of sunspot groups outside the active longitude zone. We assume that this can be due to the different depths of the bases of the different sunspot groups and to the difference in the localization of the sunspot bases and the active longitude source. As a result, only a portion of the groups can consistently receive magnetic flux from a faster rotating source, which leads to an acceleration of their rotation.