Ephemeral active regions during solar minimum

Abstract

Ephemeral active regions (ER) identified on Kitt Peak daily full-disk magnetograms from April through November 1975 were analyzed and compared with larger active regions during the same interval. The 1975 ER were also compared with ER data from 1970, 1973, 1976, and 1977. ER were found to vary approximately with the sunspot cycle. However, a minimum in the number of ER occurred at least one year prior to sunspot minimum. All evidence to date indicates that the early ER minimum was due to the rise of solar cycle 21 primarily in the form of ER. ER were statistically identified as belonging to both outgoing solar cycle 20 and incoming cycle 21 by maxima in their distribution in latitude and by their statistically dominant orientation as a function of latitude. From the identification of ER with specific solar cycles and the persistent presence of high latitude ER maxima since 1970, it is suggested that the outgoing and incoming solar cycles may co-exist on the sun longer than the 0–3 year period of overlap between successive cycles already known from the properties of large sunspot-producing active regions.