North-south asymmetry of some solar indices

The smoothed values of the N-S asymmetry of the particular solar parameter LA (longitudinal asymmetry of vectorial sunspot area) were shown by Vernova et al. (Solar Phys. 205 (2002) 371-382) to have an average pattern about the zero epoch, wherein the oscillation starts by a northern dominance (N-S positive) of LA value in the ascending phase of the solar cycle which lasts for about 2-3 years, followed by a southern dominance (N-S negative) 1.2-1.7 years later. The southern dominance (N-S negative) lasts for about 1.6 years and ends slightly before the end of the magnetic reversal (zero epoch). In the present communication, these patterns were studied for two other solar indices, namely, solar flare index (SFI) and solar group area (SGA), for solar cycles 21 and 22. It was noticed that (a) the patterns for SFI and SGA were very similar to each other (correlation +0.92), (b) the large northern dominance (N-S positive) 2-3 years before the zero epoch in the average pattern was seen in SFI using the same zero epochs (1981.8 for cycle 21 and 1991.8 for cycle 22) as Vernova et al. (2002), (c) the large southern dominance (N-S negative) ∼1 year before the zero epoch in the average pattern was seen in SFI in cycle 21, but in cycle 22, the N-S trough was at or after the zero epoch (not one year earlier), (d) after the zero epoch, the average pattern was supposed to be rather quiet. However, in cycle 21, SFI had large N-S troughs (southern dominance) after the zero epoch, while in cycle 22, SFI had a broad N-S trough near the zero epoch, (e) in cycles 21 and 22, SFI had fluctuations with peak spacings of 15-20 months before the zero epoch.