Prediction of the annual maximum sunspot number for Solar Cycles 22, 23, 24 and 25 via the geomagnetic activity indices aa and Ap

In this work, we calculate the upper limit of the annual number of sunspots in solar cycles 22, 23, 24 and 25 via the precursor method. The geomagnetic activity observed during the last four years of the closing phase of solar cycles has been used for forecasting the annual maximum number of sunspots during solar cycles. Using the indices aa* = 16.48 and Ap* = 8.45, we estimated the upper limits of the annual number of sunspots in solar cycle 25 to be 119.71 ± 43.29 and 115.92 ± 43.29, respectively. We have also verified this method by predicting the number of annual maximum sunspot numbers for the last three solar cycles (22, 23, and 24). The precursor technique has been proven to be valid for forecasting the peak annual number of sunspots during solar cycles. We have also discussed the prediction of the amplitude of the solar cycle 25 via different techniques such as the surface flux transport (SFT) model method, the Hurst exponent analysis method, the neural network method, and the Shannon entropy method. PACS No.: 95.85 Ry, 96.60 Qc.1.