Solar and geomagnetic activity during cycle 21 and implications for cycle 22

Abstract

Old Cycle 21 ended and new Cycle 22 began in September 1986. As measured by its sunspots, the new cycle of solar activity is rising more rapidly than any previous cycle in the records dating back to 1755 A.D. Progress of the new cycle—expected to last about 11 years—is of interest because terrestrial satellite missions and other technical systems are affected by various forms of solar activity; all forms of activity rise more or less in concert with the sunspots of the new cycle. In consequence, the solar output also varies. For example, the slowly varying background ultraviolet flux varies, affecting the density of the terrestrial thermosphere. In turn, satellite drag and radio propagation effects vary. Flares, energetic solar proton events, and geomagnetic storms occur in cycles that begin and end about the same time as the sunspot cycle but do not track it as well as t h e slowly varying radiation. The exceptionally rapid rise of the new cycle is the basis for prediction of a cycle of record amplitude with smoothed sunspot numbers ∼200 and smoothed 10.7‐cm solar radio flux ∼250, which would equal or exceed the largest cycles of the past. Cycle 19, the largest recorded, peaked in 1958 with a smoothed sunspot number of 201. Methods based on observation of antecedent phenomena in Cycle 21 predict that Cycle 22 will have a large maximum sunspot number well above average but not record equaling. At the present time, there is no consensus regarding which group of predictions is likely to be the more valid. Nonetheless, it appears increasingly likely that Cycle 22 will reach a peak sunspot number well above the average of all previous cycles. In another 6–12 months we expect to have a better idea of the maximum yet to come.