The Relationship Between the Amplitude and Descending Time of a Solar Activity Cycle

The amplitude of a solar-activity cycle is found to be well correlated (r = -0.811) with the descending time three cycles earlier, in smoothed monthly-mean sunspot numbers for Cycles 8 - 23. The descending time therefore can be used as one of the indicators to predict the amplitudes. As a result, the amplitudes of Cycles 24 - 25 are estimated to be 114.8 c 17.4, 111.6 c 17.4, respectively, where the error bar equals c standard error.