A Solar Analog Model for Decrease in Far Ultraviolet Irradiance Under a Grand Minimum

Abstract Solar analog field stars having a range of magnetic activity can provide an estimate of solar spectral irradiance (SSI) variability relevant to understanding the Sun's influence on terrestrial climate. This approach is particularly useful for far ultraviolet (FUV) irradiance that cannot be observed from the Earth surface. The International Ultraviolet Explorer (IUE) made numerous observations of Sun‐like stars between 1978 and 1996. Using Gaia parallax data, we identified 53 stars observed by IUE as cool main sequence stars similar to the Sun and having measurements of magnetic activity ranging from very active to very inactive analogous to a grand minimum. From these observations we estimate the decrease in FUV SSI from a typical solar cycle minimum to a grand minimum analogous to the historical Maunder minimum, in eight spectral bands between 125 and 198 nm. While the shortest wavelength band has a large uncertainty in the estimate, we find that from a typical solar cycle minimum to a grand minimum the irradiance difference varies from 5.3% to 19.3% as wavelength decreases from 195 to 135 nm. Our corresponding IUE‐based estimate from a representative solar maximum to solar minimum is consistent with NASA Upper Atmosphere Research Satellite (UARS) Solar‐Stellar Irradiance Comparison Experiment (SOLSTICE) observations, for wavelengths longer than 135 nm. These results provide motivation for potential future surveys with more current space‐based instruments and can also help constrain climate data records.