Modeling solar extreme ultraviolet irradiance variability using emission measure distributions

Abstract

We introduce a new model of solar irradiance variability at extreme ultraviolet (EUV) wavelengths. The model combines a spectral emission line database, solar emission measure distributions, and estimates from ground‐based solar images of the fraction of the Sun covered by the various types of activity to synthesize the irradiance. Using Call K‐line images, the model can be used to estimate the irradiance from EUV line emission formed in the upper chromosphere and lower transition region. Comparisons of this new model with existing empirical models reveal both similarities and disagreements in the absolute magnitude, the amplitude of the rotational modulation, and the intermediate‐term solar cycle variability of the predicted fluxes.