This plot provides a look at the progression of the smoothed NWRA effective sunspot number (SSNe) for solar cycles 23 and 24. The heavy solid curve is the smoothed SSNe (centered 13-month average), the light solid curve is the monthly average SSNe, and the dashed curve is a sunspot number calculated from the smoothed F10.7 solar flux. The foF2 data used in the SSNe calculations were obtained from the National Centers for Environmental Information (NCEI), and the 10.7cm solar flux data were obtained from the Dominion Radio Astrophysical Observatory (DRAO).
The red curves extending beyond the current date are extrapolations based on the latest prediction for Cycle 25 provided by the NOAA SWPC. That prediction (as of 21 June 2020) gives an expected solar minimum in early 2020, a maximum occurring in July 2025 (+/- 8 months), and a sunspot range of 105 to 125. What is wanted here is a projection for SSNe that is consistent with the SWPC SSN prediction. The peak smoothed SSN (new scaling) for Cycle 24 was 115, and the smoothed SSNe was 90. Since the SWPC prediction for the Cycle 25 peak is SSN=115, we will used a maximum SSNe of 90. The central solid curve uses the July 2025 date and 90 maximum value. The upper dashed curve shown here uses the earliest date for maximum and the higher sunspot number of 100 and the lower dashed curve uses the latest maximum date and lower sunspot number of 80. All curves assume that the latest solar minimum occurred in January 2020. These curves represent a current best-estimate of the range of the 13-month smoothed effective sunspot number over the next three years.
Please note that the SSNe values plotted here were calculated in near real-time from a limited data set. If you are interested in post-analysis SSNe values calculated from a more representative data set, please contact NWRA.
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