HR: 1340h
AN: SH53A-0303    [Abstracts]
TI: Implications of Ground Based Photometric Images for Long Term Solar Irradiance Variations
AU: * Walton, S R
EM: stephen.walton@csun.edu
AF: San Fernando Observatory CSUN, 18111 Nordhoff St., Northridge, CA 91330-8268
AU: Preminger, D G
EM: dora.preminger@csun.edu
AF: San Fernando Observatory CSUN, 18111 Nordhoff St., Northridge, CA 91330-8268
AU: Chapman, G A
EM: gary.chapman@csun.edu
AF: San Fernando Observatory CSUN, 18111 Nordhoff St., Northridge, CA 91330-8268
AB: The San Fernando Observatory (SFO) has produced photometric full disk solar images at 5 arc second resolution since 1986, and 2.5 arc second resolution since 1989. We have previously shown that the best quantities for solar irradiance modeling are the {\em photometric sums} $\Sigma$, defined as the summed residual intensity on these photometric images. In particular, a linear regression of total solar irradiance $S$ to the time series of $\Sigma_r$ and $\Sigma_K$, the photometric sums in broadband red and Ca~II~K filters, respectively, does an excellent job of reproducing $S$ during cycle 22 (Preminger, Walton, and Chapman 2002, {\it JGR} {\bf 107}, Issue A11, SSH 6-1). We have also shown (Walton, Preminger and Chapman 2003, {\it Solar Phys.} {\bf 213}, 301) that variations in the chromospheric network appear to account for no more than 25% of the change in $S$ over the solar cycle. In this talk, we extend these results to cycle 23 and discuss their implication for long term changes in $S$. In particular, if $\Sigma_r = \igma_K = 0$ can be taken as representing the complete absence of solar activity, then one would conclude that the minimum level of $S$ is not much below those currently observed at solar minimum; quantitatively, about 0.3 W~m$^2$ below that level.
DE: 7536 Solar activity cycle (2162)
DE: 7538 Solar irradiance
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting