LAUSR

In most of the solar cycles, activity in the northern and southern hemispheres peaks at different times. One hemisphere peaks well before the other and at least one of the hemispheric maxima frequently does not coincide with the whole sphere maximum. Prediction for the maximum of a hemisphere and the corresponding north–south asymmetry of a solar cycle may help to understand the mechanism of the solar cycle, the solar-terrestrial relationship, and solar-activity influences on space weather. Here we analysed the sunspot-group data from the Greenwich Photoheliographic Results (GPR) during 1874 – 1976 and Debrecen Photoheliographic Data (DPD) during 1977 – 2017 and studied the cycle-to-cycle variations in the values of 13-month smoothed monthly mean sunspot-group area in the whole sphere (WSGA), northern hemisphere (NSGA), and southern hemisphere (SSGA) at the epochs of maxima of Sunspot Cycles 12 – 24 and at the epochs of maxima of WSGA, NSGA, and SSGA Cycles 12 – 24 (note that solar-cycle variation of a parameter is expressed as a cycle of that parameter). The cosine fits to the values of WSGA, NSGA, and SSGA at the maxima of sunspot, WSGA, NSGA, and SSGA Cycles 12 – 24, and to the values of the corresponding north–south asymmetry, suggest the existence of a ≈132-year periodicity in the activity of the northern hemisphere, a 54 – 66year periodicity in the activity of the southern hemisphere, and a 50 – 66 year periodicity in the north–south asymmetry in activity at all the aforementioned epochs. By extrapolating the best-fit cosine curves we predicted the amplitudes and the corresponding north–south asymmetry of the 25th WSGA, NSGA, and SSGA cycles. We find that on average Solar Cycle 25 in sunspot-group area would be to some extent smaller than Solar Cycle 24 in sunspot-group area. However, by inputting the predicted amplitudes of the 25th WSGA, NSGA, and SSGA cycles in the linear relationship between sunspot-group area and sunspot number we find that the amplitude (130 ± 12) of Sunspot Cycle 25 would be Bikasipura, Bengaluru-560 111, India Formerly worked at Indian Institute of Astrophysics, Bengaluru-560 034, India. corref, email: [email protected]; email:jdotjavaraiah@gmail. com; email: [email protected] SOLA: pasym-corrected.tex; 1 March 2022; 2:32; p. 1