SIMPLE METHODS FOR PREDICTING THE SIZE AND TIMING OF SUNSPOT CYCLE 25

ADDITIONAL REMARKS

Abstract

A simple method based on the number of continuous months bounding sunspot minimum occurrence with smoothed monthly mean sunspot number R <20 (i.e., N(R<20)) is found to be useful for predicting the size and timing of a sunspot cycle (SC). In particular, an SC having N(R<20) <19 months tends to have a larger sunspot minimum (Rm) and maximum (RM) amplitude and a shorter ascent (ASC) and period (PER), while an SC having N(R<20)  ≥19 months tends to have a smaller Rm and RM and a longer ASC and PER. SC25, the present ongoing cycle, had N(R<20) = 43 months, suggesting Rm = 5.6 ± 4.6, RM = 144.2 ± 43.5, ASC = 59 ± 14 months and PER = 132 ± 14 months. Instead, based on inferred regression equations and using N(R<20) = 43 months, SC25 is expected to have Rm = 3.6 ± 2.8, RM = 130.9 ± 39.7, ASC = 62 ± 11 months and PER = 137 ± 14 months. For SC25, Rm = 1.8 occurred in December 2019 and R exceeded 116.4 (SC24’s RM) in February 2023. Therefore, SC25’s RM will be larger than that observed for SC24 and not smaller. For SC25, RM = 148.5 ± 21.1 is the projected value based on the average of several techniques for estimating RM. Such a value means the 2-cycle moving average for SC24 will be 140.4, some 32 units of sunspot number below that observed for SC23, further suggesting that SC24, indeed, marks the beginning of another three to five cycles of extended intervals of low sunspot number minimum- and maximum-amplitude cycles.