Abstract The concept of degree of similarity (η), is proposed to quantitatively describe the similarity of a parameter (e.g. the maximum amplitude Rmax) of a solar cycle relative to a referenced one, and the prediction method of similar cycles is further developed. For two parameters, the solar minimum (Rmin) and rising rate (βa), which can be directly measured a few months after the minimum, a synthesis degree of similarity (ηs) is defined as the weighted-average of the η values around Rmin and βa, with the weights given by the coefficients of determination of Rmax with Rmin and βa , respectively. The monthly values of the whole referenced cycle can be predicted by averaging the corresponding values in the most similar cycles with the weights given by the ηs values. As an application, Cycle 24 is predicted to peak around January 2013 ±8 (month) with a size of about Rmax = 84 ± 17 and to end around September 2019.

Keywords Sun: activity — Sun: general — sunspots

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