Version 2 of the TSIS-1 Hybrid Solar Reference Spectrum and Extension to the Full Spectrum

This work describes two achievements to a key data set. First, we present version 2 of the Total and Spectral Solar Irradiance Sensor-1 Hybrid Solar Reference Spectrum (TSIS-1 HSRS), which has recently been recognized as a new solar irradiance reference standard (). Second, we present a new "full spectrum extension" of the TSIS-1 HSRS. The TSIS-1 HSRS observational composite solar irradiance reference spectrum spans 0.202-2.730 mu m and encompasses more than 97% of the energy in the total solar irradiance (TSI). Version 2 is an incremental update that corrects the radiometric baseline between 0.202 and 0.210 mu m and updates the solar lines at wavelengths longward of 0.743 mu m to those listed in the most recent database. The full spectrum extension builds off version 2 of the TSIS-1 HSRS and supports applications that require a solar spectrum encompassing nearly 100% of the energy in the TSI. It spans 0.115-200 mu m and was developed by incorporating additional observations and theoretical knowledge where no direct observations currently exist. Plain Language Summary The Sun's irradiance spectrum is used in many applications such as constraining the solar forcing in climate models. Recently, the TSIS-1 Hybrid Solar Reference Spectrum (HSRS), a spectrum developed by adjusting high spectral resolution solar line data to the irradiance scale of the more accurate, but lower spectral resolution, Total and Spectral Solar Irradiance Sensor-1 (TSIS-1) Spectral Irradiance Monitor (SIM) and Compact SIM observations, was formally recognized as a new standard. In this work, we provide an incremental update to that reference spectrum. Furthermore, we extend it to the "full spectrum," beyond the wavelength range of direct observations of the Sun's irradiance spectrum. The HSRS Extension differs by less than 0.1% in its integral quantity to observations of the total solar irradiance. Above the range of the SIM observations, the solar line data are normalized to the irradiance scale of a theoretical spectrum and then adjusted in magnitude to match the SIM observations at their long wavelength cut-off. Below the range of the SIM observations, Solar Stellar Irradiance Comparison Experiment observations from the Solar Radiation and Climate Experiment mission are incorporated.