On the prediction of maximum amplitude for solar cycles using geomagnetic precursors

Precursor methods for the prediction of maximum amplitude of the solar cycle have previously been found to provide the most reliable indication for the size of the following cycle, years in advance. In this paper, we evaluate several of the previously used geomagnetic precursor methods and some new ones, both as single-variate and multivariate regressions. The newer precursor methods are based on the size of the geomagnetic index maximum, which, since cycle 12, has always occurred during the declining portion of the solar cycle, usually several years before subsequent cycle minimum. These various precursor techniques are then applied to cycle 23, yielding the prediction that its maximum amplitude should be about 168 +/- 15 (r.m.s.), peaking sometime in 1999-2000.