Simplex Projection Predictions of the Remainder of Solar Cycle 25 and the Next Solar Cycle 26 Based on the Monthly Mean Sunspot Numbers

Solar activity and related space weather have a significant impact on the Solar System and Earth. Therefore, reliable prediction of solar activity is becoming increasingly important. To predict the remainder of Solar Cycle 25 and the amplitude and timing of the maximum of Solar Cycle 26, we applied the Simplex Projection method to the monthly mean sunspot number (SSN). While most prediction studies rely on 13-month smoothed SSN, we deliberately used unsmoothed monthly mean SSN for long-term solar cycle postcasts and obtained quite successful single and double cycle predictions for Solar Cycles 20 – 24. We defined the “split point” between the library and prediction sets as an important setting parameter; when this parameter was optimized, prediction ability improved significantly. We predicted that Solar Cycle 26 will be slightly weaker than Solar Cycle 25 and stronger than Solar Cycle 24. Its cycle profile is expected to show either a well-defined double peak or a slightly fluctuating flat peak, both resembling Solar Cycle 20. We predicted that the Solar Cycle 25 minimum will occur in the mid-2030. For Solar Cycle 26, the maximum is predicted for June 2035 with 150.6 – 181.5 monthly mean SSN (13-month smoothed 137.4 – 146.2), and the minimum for late 2040. The similarity between Solar Cycles 20 and 26 may reflect Gleissberg Cycle modulation.