Reconstruction of solar UV irradiance since 1974

TL;DR

This paper reconstructs solar UV irradiance from 1974 to 2007 using an empirical extension of SATIRE models, revealing significant variations that impact Earth's climate studies.

Contribution

It introduces a novel reconstruction method for solar UV irradiance over multiple solar cycles using magnetogram data and SATIRE models.

Findings

Reconstructed Ly-alpha irradiance matches observed data well.

UV irradiance variations are much stronger than visible light.

Variations increase at shorter wavelengths, especially in climate-sensitive regions.

Abstract

Variations of the solar UV irradiance are an important driver of chemical and physical processes in the Earth's upper atmosphere and may also influence global climate. Here we reconstruct solar UV irradiance in the range 115-400 nm over the period 1974-2007 by making use of the recently developed empirical extension of the SATIRE models employing SUSIM data. The evolution of the solar photospheric magnetic flux, which is a central input to the model, is described by the magnetograms and continuum images recorded at the Kitt Peak National Solar Observatory between 1974 and 2003 and by the MDI instrument on SoHO since 1996. The reconstruction extends the available observational record by 1.5 solar cycles. The reconstructed Ly-alpha irradiance agrees well with the composite time series by Woods et al (2000). The amplitude of the irradiance variations grows with decreasing wavelength and in the wavelength regions of special interest for studies of the Earth's climate (Ly-alpha and oxygen absorption continuum and bands between 130 and 350 nm) is one to two orders of magnitude stronger than in the visible or if integrated over all wavelengths (total solar irradiance).