Spectral Irradiance Observations and Projections for Solar Cycle 25

Abstract The Ozone Monitoring Instrument (OMI) on the Aura satellite makes near‐daily measurements of solar spectral irradiance (SSI) at wavelengths between 265 and 500 nm for instrument calibration purposes. The low degradation and exceptional stability of OMI's calibration during its lifetime facilitates the creation of a new 18‐year OMI Version 7 data set. This data set presented here, which extends our previous data set by more than six years, is constructed using an improved OMI degradation model, and enables discussion of SSI variability during the extended 2009 solar activity minimum and subsequent Solar Cycles 24 and 25. OMI observations of solar irradiance variability in the mid‐ultraviolet (265–300 nm), near‐ultraviolet (300–400 nm), and visible (400–500 nm) spectral regions, consistent with concurrent measurements from other satellite instruments, show that, contrary to initial predictions, Solar Cycle 25 is significantly more active than Solar Cycle 24. Solar activity indices created from OMI SSI observations agree with both satellite and ground‐based indices, and are similarly higher in Solar Cycle 25 than 24. We demonstrate good agreement between the OMI irradiance observations and the new observation‐based NOAA‐NASA‐LASP (NNLSSI1) model of solar irradiance variability, including during Solar Cycle 25. The agreement is even better when the model is revised using an improved facular index that is consistent with OMI activity indices. We use the revised NNLSSI1 rev 1 model reconstruction of solar irradiance in the past century to make a simple statistical projection of SSI variability during the remaining portion of Solar Cycle 25 and beyond.