Solar cycle 23 prediction update

The smoothed sunspot number (SSN) and the planetary index (Ap) data for the period 1932 to 1998 are used to derive a relationship to compute future smoothed solar cycle maxima. We show that the amplitudes of the last six cycles (17 to 22) bear a linear correlation with the annual mean values of Ap one year into the new cycle. The observed correlation coefficient (cc) of 0.82 has a confidence level (ci) of > 95%. Based on an annual mean value of 8.5 for Ap in 1997, we predict a moderate cycle 23 with the smoothed SSN at the maximum of 131.5 + 33/-20, expected to occur late in 1999 or early in the year 2000. (C) 2000 COSPAR. Published by Elsevier Science Ltd.