Use of Kp index of geomagnetic activity in the forecast of solar activity

It is well established that geomagnetic activity in the declining phase of a solar cycle is a useful precursor of the amplitude of the solar activity in the next cycle. In the present analysis, we show that the frequency of occurrence of Kp index with values (0–1) representing geomagnetic calm and with values between 4 and 7 representing moderate geomagnetic disturbances in the declining phase of a solar cycle is linearly related to the sunspot maximum of the next cycle. Highest correlations are obtained when the frequencies are averaged over three years preceding the solar minimum epochs. We also show that the frequency of occurrence of consecutive 4 or 6 intervals of Kp with the same magnitude (0–1 or 4–5) is also equally reliable as a predictor of the ensuing solar maximum. The rate of increase of sunspot number to the solar maximum and its subsequent rate of decline to the next minimum can also be predicted reliably with these frequencies. Based on the observations for 1993–1996, we expect the coming solar maximum to be associated with an annual mean sunspot number of about 140, with a rate of ascent of 35/year and a decline rate of about 25/year.