Predicting the Amplitude of Solar Cycle 25 Using the Value 39 Months Before the Solar Minimum

Abstract

Yoshida and Yamagishi (Ann. Geophys. 28, 417, 2010) found that the rate of decrease in the smoothed monthly mean sunspot number [$R_{\mathrm{I}}$] over the final three years of a solar cycle or $R_{\mathrm{I}}$ itself at three years before the solar minimum [$R_{ \mathrm{min}}$] can be used as a precursor for the ensuing maximum amplitude [$R_{\mathrm{m}}$] if the time of $R_{\mathrm{min}}$ can be predicted in advance. The $R_{\mathrm{I}}$ series of the new version is employed to carefully analyze the decrease rate [$\beta$] at different months [$m$] before $R_{\mathrm{min}}$ and over different time intervals [$\Delta m$] in this study. It is found that $R_{\mathrm{m}}(n)$ of Solar Cycle $n$ is best correlated ($r=0.831$) with the preceding $\beta (n-1, m, \Delta m)$ over the final $\Delta m=m=39$ months. In addition, $R_{\mathrm{m}}$ is found to be best correlated ($r=0.834$) with the $R_{\mathrm{I}}$ value 39 months before the preceding minimum. For the even- (odd-)numbered cycles, $R_{\mathrm{m}}$ is best correlated, $r=0.956$ (0.747), with the rate of decrease over $\Delta m= 38 (43)$ months interval from $m=39(47)$ months before the solar minimum, and $R_{\mathrm{m}}$ is best correlated, $r=0.964(0.739)$, with the $R_{\mathrm{I}}$-value 39 (46) months before the solar minimum. Based on this method and the inferred end time of Solar Cycle 24, the amplitude of Solar Cycle 25 is predicted to be $R_{\mathrm{m}}=130.0\pm 31.9$, occurring around October 2024 $\pm 13$ (months).