Spectral Irradiance Modeling and Long Term Trends

Juan Fontenla [juan.fontenla@lasp.colorado.edu] and Jerald Harder, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder.

    Using observations from the Photometric Precision Telescope at Hawaii (PSPT) and the Solar Radiation Physical Modeling (SRPM), we have modeled spectral irradiance variations due to the solar activity features observed on the solar disk. This modeling is based on published spectra at mid spatial-resolution and a large number of other published observations. The current models clearly explain the observed quiet-Sun spectral irradiance in the visible and infrared but improvements are still needed in the ultraviolet. When we compare the spectral irradiance variations model results with those observed thus far by SIM, we find that including a penumbrae model is critical to improving the agreement. While many variations are fully understood, others are not yet accounted for by the well known sunspot umbrae and penumbrae, faculae and plage, and active and quiet network. We will discuss improvements to the solar image observations and the modeling that could solve some of these discrepancies.

            We will examine the observed total solar irradiance (TSI) solar cycle variation in the context of the integral of the spectral irradiance and the role of plage and faculae. In addition, we will explore potential sources for the discrepancies between the modeling estimates and the observations and their implications regarding the causes of possible long term trends in the TSI and spectral irradiance variations.