Solar irradiance models and measurements: a comparison in the 220 nm to 240 nm wavelength band

TL;DR

This paper compares modeled and measured solar irradiance in the 220-240 nm band, revealing good short-term agreement but significant discrepancies in long-term trends, especially in the SORCE data.

Contribution

It provides a detailed comparison between SATIRE-S model predictions and satellite measurements for spectral solar irradiance in the UV range.

Findings

Good agreement on rotational time scales.

Significant differences in long-term trend predictions.

SORCE instruments show steeper decline than models and other measurements.

Abstract

Solar irradiance models that assume solar irradiance variations to be due to changes in the solar surface magnetic flux have been successfully used to reconstruct total solar irradiance on rotational as well as cyclical and secular time scales. Modelling spectral solar irradiance is not yet as advanced, and also suffers from a lack of comparison data, in particular on solar-cycle time scales. Here we compare solar irradiance in the 220 nm to 240 nm band as modelled with SATIRE-S and measured by different instruments on the UARS and SORCE satellites. We find good agreement between the model and measurements on rotational time scales. The long-term trends, however, show significant differences. Both SORCE instruments, in particular, show a much steeper gradient over the decaying part of cycle 23 than the modelled irradiance or that measured by UARS/SUSIM.