The predicted size of cycle 23 based on the inferred three-cycle quasi-periodicity of the planetary index Ap

A review of the solar and the geophysical data for the last 6 decades indicates the existence of a three-solar-activity-cycle quasi-periodicity in them. It is also present in other data sets extending over several centuries. A new cycle may have started after 1996. If true, cycle 23 will be more modest (a la cycle 17) with an annual mean sunspot number count of 119.3 +/- 30 at the maximum. This inference is in contrast to the predictions of some of the solar astronomers who are predicting a very active cycle 23 (a la cycle 19).