Evolution of the solar irradiance during the Holocene

Abstract

Context. Long-term records of solar radiative output are vital for understanding solar variability and past climate change. Measurements of solar irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models. Aims. We present a physically consistent reconstruction of the total solar irradiance for the Holocene. Methods. We extend the SATIRE (Spectral And Total Irradiance REconstruction) models to estimate the evolution of the total (and partly spectral) solar irradiance over the Holocene. The basic assumption is that the variations of the solar irradiance are due to the evolution of the dark and bright magnetic features on the solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total solar irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. In order to evaluate the uncertainties due to the evolution of the Earth's magnetic dipole moment, we employ four reconstructions of the open flux which are based on conceptually different paleomagnetic models. Results. Reconstructions of the TSI over the Holocene, each valid for a different paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth's magnetic dipole moment. The analysis of the distribution functions of the reconstructed irradiance for the last 3000 years, which is the period that the reconstructions overlap, indicates that the estimates based on the virtual axial dipole moment are significantly lower at earlier times than the reconstructions based on the virtual dipole moment. We also present a combined reconstruction, which represents our best estimate of total solar irradiance for any given time during the Holocene. Conclusions. We present the first physics-based reconstruction of the total solar irradiance over the Holocene, which will be of interest for studies of climate change over the last 11 500 years. The reconstruction indicates that the decadally averaged total solar irradiance ranges over approximately 1.5 W/m 2 from grand maxima to grand minima.

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.…”

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

“…These follow the protocol of the Paleoclimate Modeling Intercomparison Project, Phase 3 (PMIP3) (Schmidt et al 2011;Braconnot et al 2012). Prescribed external forcing factors are: variations in volcanic aerosols (Crowley and Unterman 2012), in total solar irradiance (TSI) (Vieira et al 2011) and in the atmospheric concentration of the most important well-mixed greenhouse gases and anthropogenic aerosols (Schmidt et al 2011); changes in global land-cover and agricultural areas (Pongratz et al 2008); and annual values of the orbital parameters, that is, eccentricity, obliquity, and perihelion. In addition, we use an 1156-year-long control simulation under constant preindustrial (1850) boundary conditions (hereafter PiControl) as a reference for the forced experiments.…”

“…Horizontal solid lines are the discrete levels extracted following the algorithm described in Little et al (2011). b Annual globally averaged values of the reconstructed TSI (black line, in W/m 2 ) (Vieira et al 2011) and the simulated volcanic forcing, shown as net adiative flux anomalies, long plus short waves (LW + SW, in W/m 2 ), at the top of the atmosphere with respect to the climatological mean. The volcanic forcing is for Past1000-R3.…”

Confronting a solar irradiance reconstruction with solar and stellar data

“…This unavoidable fact is at the heart of all reconstructions, even those that build in intermediate physical models (e.g. Wang et al 2005;Vieira et al 2011). Noting that "a proxy for the long-term activity of the quiet Sun does not yet exist", S2011 hypothesized that centennial time-scale QS brightness changes vary linearly with large-scale variations associated with the heliospheric solar magnetic field.…”