Spectral irradiance variations: Comparison between observations and the SATIRE model on solar rotation time scales

TL;DR

This study compares observed and modeled spectral irradiance variations over three solar rotations in 2004, validating the SATIRE model's accuracy across UV to NIR wavelengths and identifying its limitations.

Contribution

It provides a detailed comparison of spectral irradiance variability between observations and the SATIRE model, highlighting areas of agreement and discrepancy on solar rotation time scales.

Findings

Good agreement between observations and model from 400 to 1300 nm.

Model captures the shift from faculae to spot dominance around 400 nm.

Discrepancies exist below 220 nm and in some NUV lines.

Abstract

Aims: We test the reliability of the observed and calculated spectral irradiance variations between 200 and 1600 nm over a time span of three solar rotations in 2004. Methods: We compare our model calculations to spectral irradiance observations taken with SORCE/SIM, SoHO/VIRGO and UARS/SUSIM. The calculations assume LTE and are based on the SATIRE (Spectral And Total Irradiance REconstruction) model. We analyse the variability as a function of wavelength and present time series in a number of selected wavelength regions covering the UV to the NIR. We also show the facular and spot contributions to the total calculated variability. Results: In most wavelength regions, the variability agrees well between all sets of observations and the model calculations. The model does particularly well between 400 and 1300 nm, but fails below 220 nm as well as for some of the strong NUV lines. Our calculations clearly show the shift from faculae-dominated variability in the NUV to spot-dominated variability above approximately 400 nm. We also discuss some of the remaining problems, such as the low sensitivity of SUSIM and SORCE for wavelengths between approximately 310 and 350 nm, where currently the model calculations still provide the best estimates of solar variability.