Title: Solar Irradiance Variability at Short and Long Wavelengths
Author: Dora G. Preminger
Affil: San Fernando Observatory, Cal State Northridge
Email: dora@sfo.csun.edu
Authors: Stephen R. Walton, Gary A. Chapman, Angela M. Cookson
Abstract: We present recent results from the modeling of the total solar irradiance S
using photometric proxies from the San Fernando Observatory.
Our best fit to Cycle 22 comes from using the photometric
sum P, which is the sum over an entire image of each pixel's contribution to
the irradiance in that image.
P combines both bright and dark features;
since the sum is over the entire image, it will include low-contrast features
which cannot be identified using contrast criteria.
Specifically, we use 
and 
,
the photometric sums over broadband red
images and 10Å bandpass Ca II K images, respectively.
and represent the contribution to S of variability
in two wavelength bands placed on either side of the
intensity peak of the sun's spectrum.
Thus, they represent the long and short-wavelength contributions to variations
in S.
A linear combination of these two indices over cycle 22 from mid-1988 through
early 1996 models the observed composite S with a regression coefficient
.
In particular, there is no systematic difference in the residual at solar
maximum compared to solar minimum.
We also find that has no long-term
trend, but has approximately the same average value throughout the solar cycle.
, however, has a higher average value at maximum than at minimum.
Therefore, the entire long-term change in S in this model is accounted for
by the variability in the shorter wavelengths.