Modeling Solar Spectral Irradiance from Iron Lines Using the CODET Model Version 1.1

Abstract The COronal DEnsity and Temperature (CODET) model is a physics-based model. This model uses the relationship between the magnetic field, density, temperature, and extreme ultraviolet (EUV) emission. This model provides mean daily solar spectral irradiance (SSI) time series in EUV wavelengths in long timescales from days to solar cycles. The current manuscript presents the updated/new CODET model version 1.1. It uses observational data sets from the Solar Dynamics Observatory EUV Variability Experiment (SDO/EVE) MEGS-A at 28.4 and 21.1 nm wavelengths to obtain the goodness of fit between them and the modeled SSI from 2010 April 30 to 2014 May 26. The model described well observational data during that period, with less than 20% error in both wavelengths. Additionally, SSI predictions are provided using the new model parameters from 1996 July to 2024 October, where the Michelson Doppler Imager (MDI) and the Helioseismic and Magnetic Imager (HMI) photospheric magnetic field data are available. These predictions were compared with GOES/EUVS at 28.4 nm and mean daily values of the SDO Atmospheric Imaging Assembly at 21.1 nm data, with errors of ∼26% and 42% for 28.4 and 21.1 nm, respectively. The error analysis for model fitting and predictions shows how accurate the model predictions are. Thus, the CODET model provides a reliable estimate of the SSI time series in EUV wavelengths where no observational data are available, e.g., after the SDO/EVE MEGS-A era.