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

Abstract

A new database of individual solar features has been compiled fromthe full-disk photometric Ca II K images taken at the San FernandoObservatory (SFO) during solar cycle 22. The distribution of facularregion sizes differs at different phases of the solar cycle; thearea coverage of large active regions is reduced by a factor of about20 at solar minimum compared to solar maximum, while the smallerregions cover about half as much area at minimum as at maximum. Theirradiance contribution of large features is about 10 times greaterat maximum than at minimum, while that of small features is abouttwice as large. We have used this data set to model the fractionof variation in the total solar irradiance S that is due to solarfeatures of various sizes. The data show that large-scale brightsolar features, i.e., faculae, dominate the similar to0.1% changein S between solar maximum and solar minimum. Using a variety ofdata sets, we conclude that large active regions produce about 80%of the total change.