[Previous] | [Session 71] | [Next]
J. Harder, S. Davis, J. Fontenla, G. Rottman, O. White (LASP, University of Colorado)
The Spectral Irradiance Monitor, SIM, is now providing the first continuous record of solar irradiance variations throughout the visible and near infrared. This instrument is aboard the Solar Radiation and Climate Experiment, SORCE, which was launched in January 2003. SIM is a prism spectrometer that makes precise measurements of the solar irradiance four times a day over the entire spectral range 200-2700 nm. The SIM data provide important new information on both the mechanisms of solar variability and on how the changing Sun influences our terrestrial environment. The SIM observations will be compared with concurrent computations of the solar spectral irradiance generated from the RISE (Radiative Inputs from the Sun to the Earth) synthesis code with decompositions of PSPT (Precision Solar Photometric Telescope) images. This irradiance synthesis directly accounts for the distribution and evolution of features on the Sun that contribute to irradiance variations. The RISE method uses seven solar atmospheric models (Fontenla, Avrett, and Loeser, ApJ, 406, 319, 1993) to represent sunspots, plage, network, and quiet atmosphere. The contributions of these seven atmospheric models are then weighted according to the decomposition of the solar images. Time series comparisons at visible wavelengths between the model and the SIM observations indicate good agreement. However, current models of IR spectral irradiance are inaccurate at long wavelengths; this behavior is due to the fact that, contrary to the current model assumptions, the presence of active regions on the solar disk increase the spectral irradiance at all wavelengths even near the opacity minimum at 1.6 microns in a manner similar to the observed TSI. Consequently, calculations of solar spectral irradiance at wavelengths near 1.6 microns need to be revised to match the observed solar irradiance.
[Previous] | [Session 71] | [Next]
Bulletin of the American Astronomical Society, 36 #2
© YEAR. The American Astronomical Soceity.