UV solar irradiance in observations and the NRLSSI and SATIRE-S models

TL;DR

This paper reviews UV solar irradiance measurements and models, comparing NRLSSI and SATIRE-S, highlighting their differences, uncertainties, and recommending SATIRE-S for climate research due to its consistency with observations.

Contribution

It provides a comprehensive comparison of UV solar irradiance models and measurements, clarifying their reliability and guiding model selection for climate studies.

Findings

SATIRE-S aligns well with spectral irradiance observations

NRLSSI's solar cycle variability is affected by observational uncertainties

SATIRE-S is recommended for climate-related applications

Abstract

Total solar irradiance and UV spectral solar irradiance have been monitored since 1978 through a succession of space missions. This is accompanied by the development of models aimed at replicating solar irradiance by relating the variability to solar magnetic activity. The NRLSSI and SATIRE-S models provide the most comprehensive reconstructions of total and spectral solar irradiance over the period of satellite observation currently available. There is persistent controversy between the various measurements and models in terms of the wavelength dependence of the variation over the solar cycle, with repercussions on our understanding of the influence of UV solar irradiance variability on the stratosphere. We review the measurement and modelling of UV solar irradiance variability over the period of satellite observation. The SATIRE-S reconstruction is consistent with spectral solar irradiance observations where they are reliable. It is also supported by an independent, empirical reconstruction of UV spectral solar irradiance based on UARS/SUSIM measurements from an earlier study. The weaker solar cycle variability produced by NRLSSI between 300 and 400 nm is not evident in any available record. We show that although the method employed to construct NRLSSI is principally sound, reconstructed solar cycle variability is detrimentally affected by the uncertainty in the SSI observations it draws upon in the derivation. Based on our findings, we recommend, when choosing between the two models, the use of SATIRE-S for climate studies.