Spatial distribution of the N-S asymmetry of solar activity and its time variations

Abstract

The 1943–2001 data on the brightness of the coronal green λ530.3 nm line are used to investigate the surface distribution of the north-south (N-S) asymmetry index A. Synoptic maps of the asymmetry index in 784 successive Carrington rotations have been constructed. The results are presented in the form of a movie that visualizes the time variation in the spatial distribution of the asymmetry. Examination of a series of synoptic maps shows that the time variation in the general distribution of the A index over the solar surface has a number of peculiar features. In particular, the latitude-longitude regions with the dominance of the green line brightness in one of the hemispheres are replaced by similar (in shape) regions with its dominance in the other hemisphere after 14–18 rotations-in other words, the map, as it were, turns into its negative. This may be a manifestation of the quasi-biennial oscillations in the N-S asymmetry. The synodic rotation period of the asymmetry “structures” has been determined. It has turned out to be equal to the period of the fast coronal rotation mode found previously from the large-scale brightness distribution of the coronal green line, i.e., this is 27 days on the equator and slightly more than 28 days at high latitudes. The N-S asymmetry and its characteristics should be taken into account when considering the dynamo mechanism.