Physical Synthesis of the Solar Radiance, a Tool for Understanding Spectral Irradiance

Authors: Juan Fontenla (1), O. R. White (2), E. H. Evrett (3), G. Rottman (1),

P. Fox (2), J. Harder (1), S. Davis (1)

Affiliations: 1) LASP, University of Colorado

2) HAO, NCAR

3) Center for Astrophysics, Harvard-Smithsonian Institution, Cambridge, MA

In this paper we summarize the current status of our physical modeling of the solar radiation and briefly describe the key improvements in the methods we use to compute synthetic solar spectrum.

We use 7 solar atmosphere models for summarizing the features observed on the solar disk, and we compute the emitted spectrum at 10 positions on the disk. These models and disk positions are intended to cover the significant features of quiet and active Sun that are linked with solar irradiance variations. The calculation is extremely detailed and each of the many thousands of spectral lines is fully resolved so that the spectra can be convolved with any instrument function and compared with observations at high or low spectral resolution.

Our Version 1 code and models provide very good agreement with observations of spectral irradiance between ~150 and ~1000 nm, but is not accurate outside that range. We describe the basic procedures used in Version 1 and the differences with the procedures that will be used in Version 2 for improving the synthesis accuracy over a more extended wavelength rage. We expect that Version 2 will be a major step in understanding the solar spectral irradiance and its variations beyond what is currently available from any solar irradiance models.