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S.R. Walton, D.G. Preminger, G.A. Chapman (San Fernando Observatory, Cal State Northridge)
A new database of individual solar features has been compiled from the full disk photometric images taken at the San Fernando Observatory (SFO) since 1989. 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. We have used this data set to model the fraction of variation in the total solar irradiance S which is due to solar features of various sizes. The data show that large-scale solar features dominate the ~0.1% change in S between solar maximum and solar minimum; the chromospheric network produces about 15% to 25% of the total change. We have also used new total irradiance models to evaluate the plausible level of S in the absence of all magnetic activity on the sun, and conclude that S would be reduced by about 0.3 W/m2 below the level presently observed at activity minimum.
This work was supported by NSF grant ATM-9912132 and NASA grants NAG5-7191 and NAG5-7778.
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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.