Intermediate-term solar periodicities - 100-500 days

Abstract

Periodogram analyses of time series of ground-based solar observations during the past three solar cycles confirm that a periodicity near 155 days, originally detected in the occurrence rate of major solar flares, is also present in the sunspot blocking function, the 10.7 cm radio flux, and the sunspot number, but not in the plage index. This indicates that the 155 day solar periodicity is not simply a feature of flare activity alone and suggests that it is associated with those regions on the sun where magnetic fields are concentrated into small areas, such as in sunspots, but not where they are more dispersed, as in plages. The periodogram of the sunspot blocking function, 10.7 cm radio flux, sunspot number, and plage index daily data during the entire three-cycle time span each has a peak near 323 days, which supports previous suggestions that this, too, may be a real solar period. However, this period is a prominent feature only in solar cycle 21.