Predicting the Size and Timing of the Next Solar Cycle: Paper II, Based on Geomagnetic Values

  • Robert Wilson


This is the second paper in a two-part study of predicting the size and timing of the next sunspot cycle (SC)25. Paper I examined the behavior of sunspot number (R) as a predictor, based on specific markers as gleaned from SC24. This paper (Paper II) examines the Aa and Ap geomagnetic indices, as well as the number of disturbed days (NDD), to effect the prediction for the size and timing of SC25. Presently (as of September 2019), SC24 is in the midst of what appears to be an extended solar minimum, with R, Aa, Ap, and NDD all of extremely low value and the nonoccurrence of any new cycle high latitude sunspots. Paper II describes methods for estimating the size of an SC and sets upper limits to the size of SC25. A definitive prediction cannot be made at this time but can be made when the minimum values of Aa, Ap, and NDD actually become available—probably in 2020 or more likely 2021.