Solar spectral irradiance reconciliation of SORCE and TSIS1 SIM

The Solar Radiation and Climate Experiment (SORCE) recorded daily Solar Spectral Irradiance (SSI) measurements from 2003 to 2020, overlapping with the Total and Spectral Irradiance Sensor (TSIS1) for ∼2 years (Mar. 2018 - Feb. 2020). We use data from the Spectral Irradiance Monitors (SIM), spanning 704 days and 554 time-matched observations, to compare absolute irradiance calibrations in a truly unique space-based UV-IR spectroscopic overlap study. This 200–2400 nm comparison was conducted during the Solar Cycle 24 minimum, so observed differences are likely instrumental. We find peak-to-peak (maximum) absolute scale differences of 12% with a mean fractional difference of 0.7 ± 2.9%. A multiplicative scale correction factor (STICR) has been developed to reconcile the TSIS1 and SORCE SIM irradiance differences. Applying this correction to the SORCE-SIM V27 dataset, we provide a re-calibrated dataset known as the TSIS1-SIM Adjusted Values (TAV). We discuss the challenges in the creation of STICR and TAV, and lessons learned about using temporally overlapping space observatories to provide a continuous solar observation record.