An Improved Model for Daily Solar Spectral EUV Irradiance Highlighting Temperature-Based Active Region Variations

Abstract:

EUV and XUV radiation from the Sun is absorbed by and ionizes the atmosphere, creating both the ionosphere and thermosphere. Temporal changes in irradiance energy and spectral distribution can have profound impacts on the ionosphere, impacting technologies such as satellite drag and radio communication. Because of this, it is necessary to estimate and predict changes in Solar EUV spectral irradiance. Ideally, this would be done by direct measurement but this is technically challenging due to the necessity for space-based measurements and difficulties including on-orbit degradation. Scientists must use data-driven models to predict the solar spectral irradiance to fill temporal and wavelength gaps in our knowledge of the solar spectral irradiance. In this study, we further develop the Synthetic Reference Spectral Irradiance Model (SynRef). The SynRef model, which uses broadband EUV irradiance data from the Extreme Ultraviolet Monitor onboard the MAVEN probe at Mars, was created to mirror the Level 4 spectral irradiance model produced by the X-ray Photometer System instruments onboard the SORCE and TIMED satellites. Both models combine weighted contributions of static theoretical Active Region (AR) and Quiet Sun spectra generated by CHIANTI to match daily measured irradiance data, and output a modeled solar EUV spectrum for that day. The advancement presented here enables the use of dynamic AR spectra by estimating AR temperature and then selecting an appropriate AR spectrum from a library of temperature-based AR reference spectra. Allowing for temperature-based AR variation at shorter wavelengths of the spectrum increases the output spectrum’s accuracy at wavelengths critical to atmospheric ionization.