What Photometric Images Have (and Haven't) Taught Us about TSI
Stephen Walton [stephen.walton@csun.edu], San Fernando Observatory, California State University, Northridge

The San Fernando Observatory (SFO) has taken daily full disk photometric images of the sun at two resolutions and in several wavelengths since 1989. Photometric quantities derived from these images have been used with great success to model the total solar irradiance (Preminger, Walton and Chapman 2002, JGR 107, Issue A11, SSH6-1), and to infer the contribution of various solar features to TSI changes (Walton, Preminger and Chapman 2003, ApJ 590, 1088). These studies were mainly based on data for cycle 22, and we are now extending them to cycle 23. Our three main research goals are: (1) computing the statistics of solar active regions and their possible variation during the solar cycle; (2) modeling of the total solar irradiance using the photometry of both individual features and the entire disk; and (3) understanding the relative contribution of various bright features to increases in total solar irradiance. We will review the evidence supporting our main conclusions to date, which are, respectively: solar active regions change in ways which affect their use in total irradiance modeling; the solar cycle change in total irradiance is dominated by changes in the line blanketing; and that large faculae dominate the solar cycle in irradiance. We are continuing to study other data sets, such as those of the HAO Precision Solar Photometric Telescope and the Solar Bolometric Imager in an effort to clarify the issues involved with all these conclusions.