The concept of degree of similarity ( \eta ) is proposed to quantitatively describe the similarity of a parameter ( e.g .
the maximum amplitude R _ { \mathrm { max } } ) 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 ( R _ { \mathrm { min } } ) and rising rate ( \beta _ { \mathrm { a } } ) , which can be directly measured a few months after the minimum , a synthesis degree of similarity ( \eta _ { s } ) is defined as the weighted-average of the \eta values around R _ { \mathrm { min } } and \beta _ { \mathrm { a } } with the weights given by the coefficients of determination of R _ { \mathrm { max } } with R _ { \mathrm { min } } and \beta _ { a } , 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 \eta _ { s } values .
Cycles 14 and 10 are found to be the two most similar cycles of Cycle 24 .
As an application , Cycle 24 is predicted to peak around January 2013 \pm 8 ( months ) with a size of about R _ { \mathrm { max } } = 84 \pm 17 and to end around September 2019 .