Revising a less-reliable prediction for the solar cycle based on the variation in correlation

The geomagnetic precursor method has been widely used to predict the maximum amplitude ( S_m ) of the sunspot cycle using the preceding minimum aa geomagnetic index ( aa_min ). The prediction error of this method was sometimes larger than expected. In the present study, a revision method is proposed to correct a less-reliable prediction in advance according to the variation in the correlation coefficient ( R ) between S_m and aa_min . For the last ten cycles n=15 –24, R was found to vary with n in a period of approximately 2 solar cycles, and most (90