Solar Spectral Irradiance Variability in the Ultraviolet during Cycle 24: Comparison of SOLAR/SOLSPEC and SOLSTICE/SORCE Data

Accurate measurements of solar spectral irradiance (SSI) and their temporal variations are of primary interest to better understand solar mechanisms and the links between solar variability and Earth's atmosphere and climate. We present recent ultraviolet SSI observations of the SOLAR/SOLSPEC spectrometer on board the International Space Station and covering the essential of the solar cycle 24, from April 5, 2008 to February 15, 2017. SOLAR/SOLSPEC data have a large wavelength coverage from the middle ultraviolet to the infrared (165 to 3000 nm). Variability is assessed, first, by a careful evaluation of the absolute reference solar spectrum observed during the 2008 solar minimum, SOLAR-ISS, which has a resolution better than 0.1 nm below 1000 nm and 1 nm in the 1000—3000 nm wavelength range, and that was recently revised in version 2 (SOLAR-ISS2), improving calibrations in UV (165-180 nm and in Herzberg 200-242nm continuum), Fraunhofer lines discontinuities corrections, and reference model in the 2400-3000nm infrared band. SOLAR/SOLSPEC variability in the UV is, then, evaluated and compared with other measurements (SORCE/SOLSTICE, SORCE/SIM) and models (SATIRE-S, NRLSSI2). Importance of results justify new measurements and missions that we shortly indicate (DEVINS detectors on UVSQ-SAT, SOLSIM SSI UV measurements on SoSWEET-SOUP, etc.).