The Contribution of Faculae and Network to Long‐Term Changes in the Total Solar Irradiance

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Abstract

A new database of individual solar features has been compiled from the full-disk photometric Ca II K images taken at the San Fernando Observatory (SFO) during solar cycle 22. The distribution of facular region sizes differs at different phases of the solar cycle; the area coverage of large active regions is reduced by a factor of about 20 at solar minimum compared to solar maximum, while the smaller regions cover about half as much area at minimum as at maximum. The irradiance contribution of large features is about 10 times greater at maximum than at minimum, while that of small features is about twice as large. We have used this data set to model the fraction of variation in the total solar irradiance S that is due to solar features of various sizes. The data show that large-scale bright solar features, i.e., faculae, dominate the ~0.1% change in S between solar maximum and solar minimum. Using a variety of data sets, we conclude that large active regions produce about 80% of the total change.

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