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

• Published in: The Journal of the Alabama Academy of Science Vol. 93; no. 2; pp. 87 - 110
• Main Author: Wilson, Robert M
• Format: Journal Article
• Language: English
• Published: Alabama Academy of Science 01.11.2022
• Subjects: Forecasts and trends; Solar cycle; United States
• ISSN: 0002-4112

This paper describes several simple methods for estimating the main features of an ongoing solar cycle (SC); in particular, its maximum amplitude (RM), ascent duration (ASC), and period (PER). The current ongoing SC25 had its minimum amplitude (Rm) in December 2019, measuring 1.8. At elapsed time t = 24 months (December 2021), smoothed monthly mean sunspot number R measured 55.7. Comparisons of R with the mean values of Fast-rising-Slow-rising and Short-PER-Long-PER cycles strongly suggest that SC25 is best described as being a Slow-rising-Long-PER SC (i.e., Slow-Long), inferring an ASC [greater than or equal to] 49 months (i.e., RM occurrence on or after January 2024) and PER [greater than or equal to] 131 months (i.e., Rm occurrence for SC26 on or after November 2030). Furthermore, RM >116.4 is expected for SC25 based on the inferred Even-Odd preferential relationship (i.e., during the modern era of sunspot observations SC12-SC24, the Odd-following SC in consecutive Even-Odd cycle pairs has usually had the larger RM, true for 5 of 6 Even-Odd cycle pairs). Slow-Long cycles (i.e., SCs 12, 14, 20, 23, and 24) have an average RM = 132.0 [+ or -] 30.6, ASC = 57 [+ or -] 7 months and PER = 138 [+ or -] 6 months. Based on the overlap of the geomagnetic minimums (i.e., Aam and Apm) in the vicinity of Rm, one estimates RM = 145.7 [+ or -] 17.1 for SC25, a value in stark contrast to the panel prediction of RM = 115 peaking in July 2025 [+ or -] 8 months. The greatest rate of growth (GRG) in R observed thus far for SC25 is only 5.6 occurring at t = 22 months (October 2021); which, if it holds up, would be the smallest GRG during the modern era (SC12-SC24) and would suggest an RM = 107.6 [+ or -] 33.4 and a mean rate of growth (MRG) = 1.7 [+ or -] 0.9 for SC25. For comparison, the smallest GRG during SC12-SC24 is 6.5 occurring at t = 39 months associated with SC14, a Slow-Long SC, having RM = 107.1, ASC = 49 months, MRG = 2.09, and PER = 138 months; SC24 had RM = 116.4, ASC = 64 months, GRG = 8.2 at t = 28 months, MRG = 1.78, and PER = 132 months.