Thompson, R.J. Sol Phys (1993) 148: 383. doi:10.1007/BF00645097
Predictions of the amplitude of the last three solar cycles have demonstrated the value and accuracy of the group of prediction methods known as the ‘precursor’ techniques. These are based on a correlation between cycle amplitude and phenomena observed on the Sun, or originating from the Sun, during the declining phase of the cycle or at solar minimum. In many cases, precursor predictions make use of the long record of geomagnetic disturbance indices, assuming that these indices are indicative of solar phenomena such as the occurrence of coronal holes.
This paper describes a precursor technique for predicting the amplitude of the solar cycle using geomagnetic indices. The technique is accurate — it would have predicted each of the last 11 cycles with a typical error of less than 20 in sunspot number. It has also advantage that a prediction of the lower limit of the amplitude can be made throughout the declining phase, this limit building to a final value at the onset of the new cycle.