THE PREDICTIVE POWER OF OHL'S PRECURSOR METHOD

Using linear regression techniques and correlation analysis, the predictive power of Ohl's method is shown to satisfy one of the following relationships. Either a successful prediction of cycle amplitude can be obtained if the correlation between the minimum aa geomagnetic index in the declining phase of a solar cycle and the sunspot maximum of the succeeding cycle becomes stronger, or the prediction error exceeds the expected prediction error if the correlation becomes weaker. The correlation coefficient has a declining secular variation, which leads to a weakening trend in predictive power, as well as a 44 year periodicity that may explain why the prediction method did not work well for solar cycle 23. As this finding only emerged twice in the ∼100 year period studied, this 44 year periodicity may occur with a degree of uncertainty and may therefore need to be checked in the future. Two quantities, namely a prediction parameter and the prediction index, are proposed to analyze predictive power. Using the above properties, the success probability of a prediction result can be analyzed in advance.