Solar-Cycle Variability Results from the Solar Radiation and Climate Experiment (SORCE) Mission

Abstract

The Solar Radiation and Climate Experiment (SORCE) was a NASA mission that operated from 2003 to 2020 to provide key climate-monitoring measurements of total solar irradiance (TSI) and solar spectral irradiance (SSI). This 17-year mission made TSI and SSI observations during the declining phase of Solar Cycle 23, during all of Solar Cycle 24, and at the very beginning of Solar Cycle 25. The SORCE solar-variability results include comparisons of the solar irradiance observed during Solar Cycles 23 and 24 and the solar-cycle minima levels in 2008 – 2009 and 2019 – 2020. The differences between these two minima are very small and are not significantly above the estimate of instrument stability over the 11-year period. There are differences in the SSI variability for Solar Cycles 23 and 24, notably for wavelengths longer than 250 nm. Consistency comparisons with SORCE variability on solar-rotation timescales and solar-irradiance model predictions suggest that the SORCE Solar Cycle 24 SSI results might be more accurate than the SORCE Solar Cycle 23 results. The SORCE solar-variability results have been useful for many Sun–climate studies and will continue to serve as a reference for comparisons with future missions studying solar variability.

Cooling and Contraction of the Mesosphere and Lower Thermosphere From 2002 to 2021

“…Woods et al. ( 2022 ), their Figure 14, show a statistically significant reduction of solar irradiance in the SRB measured by SORCE of as much as 6% from 2008 to 2009 to 2019–2020. This will reduce the heating rate in the lower thermosphere SRB by as much as 6%.…”

“…The lower thermosphere above 100 km is strongly heated through the absorption of solar ultraviolet radiation by molecular oxygen in the Schumann-Runge continuum (SRC) from 130 to 175 nm and in the Schumann-Runge Bands (SRB) from 175 to 200 nm. This critical spectral region is measured by the SEE instrument on the TIMED satellite (Woods et al, 2005) and by the SORCE satellite (Woods et al, 2022). We considered whether the solar irradiance was significantly lower during 2019-2020 than during the prior minimum from 2008 to 2009 as a possible mechanism to account for the colder SABER temperatures observed at 10 −4 hPa in 2019 than -2009.…”

“…This critical spectral region is measured by the SEE instrument on the TIMED satellite (Woods et al, 2005) and by the SORCE satellite (Woods et al, 2022). We considered whether the solar irradiance was significantly lower during 2019-2020 than during the prior minimum from 2008 to 2009 as a possible mechanism to account for the colder SABER temperatures observed at 10 −4 hPa in 2019 than -2009. Woods et al (2022, their Figure 14, show a statistically significant reduction of solar irradiance in the SRB measured by SORCE of as much as 6% from 2008 to 2009 to 2019-2020.…”

Rome Precision Solar Photometric Telescope: precision solar full-disk photometry during solar cycles 23–25

“…We recall that the TSI is the solar radiative energy flux per unit area integrated over the entire spectrum, measured at normal incidence at the top of the Earth's atmosphere and at a mean Sun-Earth distance of one astronomical unit, given in units of W m −2 , while the SSI is the analogous quantity but spectrally resolved, given in units of W m −2 nm −1 . All existing measurements show a clear TSI change by ≈ 0.1% in phase with the 11-year solar activity cycle and TSI fluctuations by up to 0.2-0.3% on timescales shorter than a few days (e.g., Fröhlich, 2013;Kopp, 2016Kopp, , 2021Montillet et al, 2022); SSI changes in the UV in phase with the solar cycle are also well established and assessed to reach several tens of percent for the radiation below 200 nm (e.g., Deland and Cebula, 2008;Woods et al, 2018;Marchenko et al, 2019;Woods et al, 2022), while there is still an uncertainty in both the phase and variability of the SSI changes in the visible and infrared ranges (Ermolli et al, 2013;Coddington et al, 2019;Dudok de Wit, 2022). Still debated is also the TSI trend on the timescales longer than the solar cycle (e.g., Kopp, 2021;Schmutz, 2021).…”

“…Fröhlich, 2013;Kopp, 2016Kopp, , 2021Montillet et al, 2022); SSI changes in the UV in phase with the solar cycle are also well established and assessed to reach several tens of percent for the radiation below 200 nm (e.g. Deland and Cebula, 2008;Woods et al, 2018;Marchenko et al, 2019;Woods et al, 2022), while there is still an uncertainty in both the phase and variability of the SSI changes in the visible and infrared ranges (Ermolli et al, 2013;Coddington et al, 2019;Dudok de Wit, 2022). Still debated is also the TSI trend on the timescales longer than the solar cycle (e.g.…”