On the prospect of using butterfly diagrams to predict cycle minimum

On the basis of butterfly diagrams for the period 1874-present (covering late cycle 11 through late cycle 21), features are identified that may be useful for predicting the beginning and the length of a solar cycle, as well as the discernment of turning points in the period-growth dichotomy. For example, the first occurrence of high latitude new cycle spots during the decline of an old cycle usually occurs in the northern hemisphere, regardless of bimodal class, about 1.4 yr before new cycle minimum or about 5.4 yr after old cycle maximum, being true for 7 out of the 10 data-available cycles. Also, the last occurrence of high latitude old cycle spots tends to occur in the southern hemisphere when the old cycle is of long period (4 out of 4 cycles) and to occur in the northern hemisphere when the old cycle is of short period (4 out of 5 cycles). Application of these sorting features to the butterfly diagram for late cycle 21 yields candidate dates for the last occurrence of high latitude old cycle spots which in every case predict that cycle 21 will be a long-period cycle, ending after July 1987. Taking April 1985 to be the first occurrence of high latitude new cycle (cycle 22) spots during the decline of cycle 21 (the old cycle), one deduces that the last occurrence of high latitude old cycle spots was September 1983 (occurring in the southern hemisphere) and predicts that minimum for cycle 22 will be about 1986.7 ± 1.1 yr, or that it should occur before the end of 1987.