Prediction of Solar Cycle 25: Maximum in the N- and S-Hemispheres

Abstract

Solar activity changes with about 11-year periodicity, two 11-year cycles form a complete 22-year magnetic cycle of the Sun. Solar cycle 25 has recently begun, and it is important to know in advance what and when it will be at its maximum. The paper predicts the maximal sunspot (Wolf) number in solar cycle 25 separately in the northern and southern hemispheres. The absolute value of the polar magnetic field near the cycle minimum was used as a precursor of the cycle maximum. The values of solar polar magnetic field measured at the Wilcox Solar Observatory of Stanford University since 1976 and sunspot numbers in the N- and S-hemispheres in 1975–2020 (in solar cycles 21–24) are analyzed. For the time interval 1992–2020, sunspot numbers in the N- and S-hemispheres were used according to SILSO ( http://sidc.oma.be/SISLO , Version 2.0), and for the time interval 1975–1992, sunspot numbers were taken from the paper (Temmer et al., 2006, Astron. Astrophys. 2006, 447, 735) and reduced to the modern SILSO scale. Sunspot numbers in minima and maxima as well as corresponding times in solar cycles 21–24 in the N- and S-hemispheres were found. The correlation coefficient at different time lags between the smoothed monthly sunspot number and the modulus of the Sun’s polar magnetic field in the northern and southern hemispheres has been calculated. It was found that maximal correlation coefficients between these parameters are 0.587 at a time lag of 4.76 years in the N-hemisphere and 0.680 at a time lag of 5.45 years in the S-hemisphere. A qualitative forecast of maximal sunspot numbers in solar cycle 25 in the N- and S-hemisphere was obtained when the graphs of the polar fields were shifted forward in time relative to the sunspot numbers graphs by 4.76 and 5.45 years, respectively. This indicates that solar cycle 25 will be slightly stronger than the previous cycle. Using the absolute values of the mean polar magnetic fields during the 2 years interval just before the cycle minimum in the N- and S-hemispheres as precursors we found that predicted maximal sunspot numbers in the N- and S-hemisphere are 66 ± 17 and 83 ± 21, respectively. This quantitatively confirms that solar cycle 25 will be slightly (4–10%) more active than the previous one.