Solar Cycle Pairing and Prediction of Cycle 25

Abstract

In addition to the Gnevyshev–Ohl rule (GOR), the relationship of an odd solar cycle with the subsequent even one in a 22-year Hale solar cycle was found. It is shown that three years before the 11-year minimum, the value of the relative sunspot number [SN] in an odd cycle is closely related to the value of the maximum in the next even cycle (the correlation coefficient $\rho =0.94$), and the same relation of an odd cycle with the previous even one is weaker. As in the GOR, cycles are linked in pairs, but when viewed in this way, the odd cycle is leading in the pair, opposite to the GOR. Based on this result, we propose to use the index of the third year before the minimum [$S\!N_{\mathrm{m}-3}$] on the descending phase of the previous odd cycle as a precursor of the subsequent even cycle. This method gives less reliable results for the prediction of an odd cycle or a prediction without consideration of parity (Brajša et al., Astron. Nachr. 343, e13960, 2022). To predict the amplitude of an odd cycle, we propose to use the seventh year before its maximum [$S\!N_{\mathrm{M}-7}$] on the descending phase of the previous even cycle. It turned out that, in this case, we can also predict years near the maximum with a high correlation coefficient ($\rho =0.90\,\mbox{--}\,0.94$). Thus, the proposed approaches allow us to predict cycles of different parity. According to our prediction, the current Solar Cycle 25 will reach a maximum at the turn of 2023 and 2024; the yearly mean SN in 2023 will be $132\pm 27$ and in 2024 SN$= 136\pm 25$. The maximum 13-month smoothed monthly mean SN will be $149\pm 28$.