Asymmetry and periodicity of solar active phenomena during cycle 23

In this paper the data of solar H-alpha flares and sunspots (Numbers and Areas) are analyzed to investigate the north-south (N-S) asymmetry and periodic variations during solar cycle 23.

The pattern of N-S distribution of these activity features shows a significant asymmetry whose dominance is changed from northern to southern hemisphere of the Sun after solar cycle maxima in 2000. The study reveals that the behaviour of N-S asymmetry for cycle 23 is quite different from cycle 22, but comparable to cycle 21.

Periodogram analysis of sunspot data (Numbers as well as areas) performed separately for northern and southern hemispheres of the Sun shows several significant Rieger-type periodicities during cycle 23. The periodic variations in the northern and southern hemishperes shows a kind of asymmetrical behaviour. On the other hand, in flare data the existence of Rieger type periodicities does not seem to be significant. The different periodic behavior of sunspot and flare activity can be understood in the light of hypothesis proposed by Ballester et al. (2002), which suggests that during cycle 23, the periodic emergence of magnetic flux partly takes place away from developed sunspot groups and hence may not necessarily increase the magnetic complexity of sunspot groups in same proportion that leads to the generation of flares.