The solar cycle: predicting the peak of solar cycle 25

Abstract

Motivated by a successful prediction on the peak of solar cycle 24 (81.7, comparable to the observed 81.9, Du in Astrophys. Space Sci. 338:9, 2012), based on the logarithmic relationship between the maximum amplitude ($R_{ \mathrm{m}}$) of a solar cycle and the preceding minimum $aa$ geomagnetic index ($aa_{\mathrm{min}}$), we perform a prediction on the peak of the upcoming cycle 25 using the sunspot number of the new version instead. If the suggested error in $aa$ (3 nT) before 1957 is corrected, the correlation between $\ln R_{\mathrm{m}}$ and $\ln aa_{\mathrm{min}}$ ($r=0.92$) is stronger than that not corrected ($r=0.86$). Based on this relationship, the peak value of cycle 25 is predicted to be $R_{\mathrm{m}}(25)\simeq 151.1\pm 16.9$, about 30% stronger than cycle 24. Employing the ‘Waldmeier effect’ that the rise time of a cycle is well anti-correlated to its amplitude, we estimated the rise time, $T_{\mathrm{a}}(25)=4.3\pm 0.2\pm 0.6$, and the peak time of cycle 25, $2024.1 \pm 0.8$ (years), which is during April 2023 and November 2024.