N–S Asymmetry in the Solar Differential Rotation During 1957–1993

Abstract

The properties of the differential rotation of the Sun are investigated by using Hα filaments as tracers. Annual average angular velocities of 716 quiescent filaments are determined from Hα photoheliograms of the Abastumani Astrophysical Observatory film collection for the years 1957–1993. The existence of north-south (N–S) asymmetry in Hα filaments rotation is confirmed statistically. The connection of asymmetry with the solar activity cycles is established. It is found that the northern hemisphere rotates faster during the even cycles (20 and 22) while the rotation of southern hemisphere dominates in odd ones (cycles 19 and 21). The mechanism of the solar activity should be responsible for the N–S asymmetry of the solar differential rotation. A theoretical explanation for the N–S asymmetry in the Sun’s rotation is offered. It is suggested that the asymmetry in the rotation of the two hemispheres of the Sun is balanced by the dynamo mechanism, which acts in parallel to the mechanism offered here. It is concluded that the N–S asymmetry of the solar rotation should cause a difference in activity level between the northern and southern hemispheres.