HR: 08:45h
AN: U41B-04 INVITED     [Abstracts]
TI: Solar Irradiance Variation on Centennial to Millennial Time Scales
AU: * Foukal, P
EM: pfoukal@world.std.com
AF: Heliophysics, Inc., 192 Willow Rd.,, Nahant, MA 01908 United States
AB: Solar irradiance variation observed over the 11 yr sunspot cycle is caused by the changing areas of dark and bright magnetic structures (sunspots, faculae)on the solar disc, but its barely 0.1 % amplitude is insufficient to drive existing climate models. Irradiance reconstructions incorporating an additional slowly varying component of sufficient amplitude to drive such models have been widely used in recent climate studies. But these reconstructions were based on results from photometry of Sun like stars which have now been largely retracted. This changed evidence challenges our understanding how solar luminosity variation could drive climate. Variation of UV flux may play a role, but its correlation with global temperature seems low, at least in the 20th century. The Sun's enormous thermal inertia restricts sources of luminosity variation on centennial to millennial time scales, to relatively superficial layers. This constraint diminishes the likelihood that deeper lying structural changes associated with e.g. the solar dynamo play a significant role. Still, some newly discovered aspects of solar magnetic behavior suggest how luminosity variation on these time scales might conceivably occur with the sign and amplitude implied by the correlations between solar activity and climate. More accurate solar and stellar observations and modeling will be required to investigate such mechanisms at the frontier of our understanding of the Sun.
DE: 7538 Solar irradiance
SC: Union [U]
MN: 2004 AGU Fall Meeting