The Sun’s irradiance varies with changes in solar magnetic activity, such as bright faculae and dark sunspots. The “contrast” of these magnetic features, relative to a specified baseline, is therefore a key element in modeling the time- and/or wavelength-dependent variability of the Sun’s irradiance. In theoretical solar and stellar atmosphere models, the contrasts are derived from the ratio of the feature atmosphere (i.e. faculae, sunspot, etc.) at some specified temperature to that of a baseline model atmosphere associated with a different temperature. Faculae and sunspot contrasts can also be derived from irradiance observations. For example, multiple linear regression of direct solar irradiance observations with proxies of faculae and sunspot activity gives wavelength-dependent coefficients that relate change in the proxies into equivalent irradiance change. Observationally-derived contrasts can be compared directly to the theoretical contrasts after applying a constant, wavelength-independent, offset factor.In this work, we use the high-fidelity solar spectral irradiance observations from the Total and Spectral Solar Irradiance Sensor (TSIS-1) Spectral Irradiance Monitor (SIM) instrument to derive faculae and sunspot contrasts. We compare the TSIS-1 SIM derived contrasts with those derived from the predecessor Solar Radiation and Climate Experiment (SORCE) mission and to the theoretical contrasts of solar and stellar atmosphere models. We conclude by discussing uncertainties in faculae and sunspot contrasts on modeled solar irradiance as, for example, by the Version 2 of the Naval Research Laboratory’s solar variability models that specify the operational NOAA Solar Irradiance Climate Data Record from the year 1610 to present day.
The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)