Solar Irradiance Variability: Modeling the Measurements

Abstract

New models of the Sun's irradiance variability are developed from 15 years of direct observations made by the Solar Radiation and Climate Experiment (SORCE) spacecraft from 2003 to 2017 (inclusive). Multiple linear regression parameterizes the observations in terms of facular brightening and sunspot darkening, which are the primary sources of solar irradiance variability. The facular influence is specified as a combination of a linear and nonlinear solar ultraviolet (UV) index; the addition of the nonlinear term allows better reproduction of concurrent solar cycle and rotational variability. The sunspot darkening index is calculated using sunspot observations from both the Debrecen catalog and Air Force Solar Observing Optical Network (SOON) operational sites, the former providing superior model performance. The new model of total solar irradiance variability, NRLTSI3, with the Debrecen sunspot index reproduces the direct Total Irradiance Monitor (TIM) observations better than does the NRLTSI2 model that currently specifies irradiance for the NOAA Climate Data Record (CDR); the correlation of the model and observations increases from 0.956 to 0.971, and the standard deviation of the residuals decreases from 0.124 to 0.100 W m−2. The new model of solar spectral irradiance variability, NRLSSI3, which extends from 115 to 100,000 nm, reproduces rotational modulation in independent Ozone Monitoring Instrument (OMI) observations at near‐UV and visible wavelengths. The SATIRE model overestimates rotational modulation of near‐UV Fraunhofer spectral features because of excess facular brightness; the EMPIRE model overestimates rotational modulation at all near‐UV wavelengths.

An Improved Solar Spectral Irradiance Composite Record

“…As shown in Figure 12a, the SSI3 composite in the EUV and FUV ranges, averaged for all four solar cycles, are compared to the predictions from FISM2 (Chamberlin, Eparvier, et al., 2020) and NRLSSI3 (Lean, Coddington, et al., 2020). The SSI3 cycle variability and FISM2 variability agree best in the wavelength ranges of 0.5–35 nm and 115–160 nm.…”

Stephan Prantner’s Sunspot Observations during the Dalton Minimum

“…These data have identified several cyclicities, such as the regular ≈ 11-year Schwabe cycles (Hathaway, 2015). These data show fairly good correlations with other physical measurements such as sunspot area and solar-irradiance fluxes, and hence used for their cross-comparisons, reconstructions, and recalibrations (Hathaway, 2015;Tapping and Morgan, 2017;Criscuoli et al, 2018;Chatzistergos et al, 2019Chatzistergos et al, , 2020Clette, 2020;Lean et al, 2020). This is also the case with the proxy data like cosmogenic isotopes, such as 14 C in tree rings, 10 Be in ice cores, and 44 Ti in meteorites (Solanki et al, 2004;Beer et al, 2012;Usoskin, 2017;Asvestari et al, 2017).…”

Overview of the Solar Radiation and Climate Experiment (SORCE) Seventeen-Year Mission

“…The NOAA CDR for SSI is similar to the TSI CDR in being a proxy model, called the NRLSSI-2 model, which was developed with the SORCE solar-irradiance observations (Coddington et al, 2016). Lean et al (2020) have the updated model version called the NRLSSI-3. Another SSI model used for climate studies is the Spectral And Total Irradiance Reconstruction (SATIRE) model (Krivova, Solanki, and Unruh, 2011).…”

“…Lean et al. ( 2020 ) have the updated model version called the NRLSSI-3. Another SSI model used for climate studies is the Spectral And Total Irradiance Reconstruction (SATIRE) model (Krivova, Solanki, and Unruh, 2011 ).…”

“…( 2016 ) and Lean et al. ( 2020 ) have updated the NRLSSI model. Additionally, the degradation trends for the SORCE instruments have been refined, bringing measurements and models into better agreement.…”