Approximation of periodicity in sunspot formation of and prediction of the 25th cycle

The empirical parameters of functions approximating solar activity cycles 8–23 are used. These parameters show the position of the cycle on the time axis (the start time) and its shape, which is characterized by the extension along the time axes and activity index. A statistical connections was found between two shape parameters of the cycle (the so-called Waldmeier effect) and between the extension of the cycle growth branch and the start time of the following cycle. A connection between the parameters of the given and future cycles has been obtained for a function approximating the “secular” variations in the cycle amplitude. The aforementioned empirical relationships can be stated in the form of three equations that contain the parameters of the current and future cycles. Solving this system, we obtain estimates for three parameters of the function approximating the next cycle. For the 25th cycle, it was found that the maximum of the smoothed Wolf number 116 is expected in March/April 2026; the duration of the activity growth branch is 4.16 years.