Reconstruction of total and spectral solar irradiance from 1974 to 2013 based on KPVT, SoHO/MDI, and SDO/HMI observations

Abstract

Context. Total and spectral solar irradiance are key parameters in the assessment of solar influence on changes in the Earth's climate. Aims. We present a reconstruction of daily solar irradiance obtained using the SATIRE-S model spanning 1974 to 2013 based on full-disc observations from the KPVT, SoHO/MDI, and SDO/HMI. Methods. SATIRE-S ascribes variation in solar irradiance on timescales greater than a day to photospheric magnetism. The solar spectrum is reconstructed from the apparent surface coverage of bright magnetic features and sunspots in the daily data using the modelled intensity spectra of these magnetic structures. We cross-calibrated the various data sets, harmonizing the model input so as to yield a single consistent time series as the output. Results. The model replicates 92% (R 2 = 0.916) of the variability in the PMOD TSI composite including the secular decline between the 1996 and 2008 solar cycle minima. The model also reproduces most of the variability in observed Lyman-α irradiance and the Mg II index. The ultraviolet solar irradiance measurements from the UARS and SORCE missions are mutually consistent up to about 180 nm before they start to exhibit discrepant rotational and cyclical variability, indicative of unresolved instrumental effects. As a result, the agreement between model and measurement, while relatively good below 180 nm, starts to deteriorate above this wavelength. As with earlier similar investigations, the reconstruction cannot reproduce the overall trends in SORCE/SIM SSI. We argue, from the lack of clear solar cycle modulation in the SIM record and the inconsistency between the total flux recorded by the instrument and TSI, that unaccounted instrumental trends are present. Conclusions. The daily solar irradiance time series is consistent with observations from multiple sources, demonstrating its validity and utility for climate models. It also provides further evidence that photospheric magnetism is the prime driver of variation in solar irradiance on timescales greater than a day.

Solar forcing for CMIP6 (v3.2)

“…On decadal to centennial timescales, SATIRE reproduces observations such as the composite of the Lyman-α line at 121.6 nm (since 1947, Woods et al, 2000), the measured solar photospheric magnetic flux (since 1967), the empirically reconstructed solar open magnetic flux (since 1845, Lockwood et al, 2014), and the 44 Ti activity in stony meteorites (Krivova et al, 2010;Vieira et al, 2011;Yeo et al, 2014). SATIRE and NRLSSI2 are internally consistent, in the sense that the integral of the modeled spectral irradiances equals the TSI.…”

“…The implementation of SATIRE employing solar images in visible light and solar magnetograms (magnetic field intensity and polarity) is termed SATIRE-S (Wenzler et al, 2005;Ball et al, 2012;Yeo et al, 2014), and that based on the sunspot number (SSN) is SATIRE-T (Krivova et al, 2010). Individual records are accessible at http://www2.mps.mpg.…”

“…In this context, and for the time being, the most reasonable approach (in a maximum-likelihood sense) consists of averaging their reconstructions, weighted by their uncertainty. Since, in addition, we are lacking uncertainties that can be meaningfully compared, our current recommendation is to simply take the arithmetic mean of the two model datasets: (i) the empirical model NRLTSI2 and NRLSSI2 (Coddington et al, 2016) and (ii) the semi-empirical model SATIRE (Yeo et al, 2014;Krivova et al, 2010). Note that multimodel averaging is a widely used practice in climate modeling (e.g., Smith et al, 2013).…”

“…All climate model intercomparison studies relied so far on the NRLSSI1 dataset (Lean, 2000). However, it is becoming increasingly evident that its solar-cycle variability in the UV part of the spectrum may be too low compared to updated and more recent SSI reconstructions by models such as NRLSSI2 (Coddington et al, 2016) and SATIRE (Yeo et al, 2014). Recent studies have emphasized the sensitivity to UV forcing changes due to top-down effects (Ermolli et al, 2013;Langematz et al, 2013;Thieblemont et al, 2015;Maycock et al, 2015;Ball et al, 2016), thereby stressing the need for a state-of-the-art representation of the SSI, and in particular the UV band, in the CMIP6 solar forcing recommendation.…”

SOLAR/SOLSPEC mission on ISS: In-flight performance for SSI measurements in the UV

“…The uncertainty for the radiometric scale of SORCE is calculated to lie between 1.2% and 6% in the UV range 6 . The same exercise was performed for the SATIRE model (Yeo et al 2014) which defined a mean SATIRE quiet Sun UV spectrum, where we selected the WHI 2008 spectrum. ATLAS 3 is associated with a certain level of solar activity, characterized by a SBUV MgII index of 0.26747.…”