Speaker
Description
Space-based measurements of solar irradiance since 1978 have revealed variability across all observable timescales. However, this record is too short to assess the Sun’s role in climate variability, making long-term irradiance reconstructions essential. From days to millennia, irradiance variability is dominated by changes in surface magnetism through the competing effects of sunspot darkening and facular brightening. Consequently, reconstructions of past irradiance variations rely on suitable proxies of solar magnetic activity.
The longest direct record of solar magnetic activity is provided by the sunspot numbers (SN), while information on facular evolution must be inferred indirectly. The SATIRE-T (Spectral and Total Irradiance Reconstructions for the Telescopic era) model reconstructs solar irradiance using the SN record as input. A recently revised version of the model is constrained by modern data, enabling an observation-based link between sunspot activity and the emergence of small-scale magnetic features such as faculae and network fields. Irradiance reconstructions based on telescopic SN show excellent agreement with direct measurements, reproducing about 90% of the observed variability.
To extend irradiance reconstructions into the pre-telescopic era, indirect proxies of solar activity are required. Concentrations of cosmogenic isotopes (14C and 10Be) preserved in terrestrial archives provide such information, but until recently these records were mostly available at decadal resolution. Recent advances in the treatment of cosmogenic isotope data have yielded annually resolved records over the past three millennia, enabling reconstructions of annual SN from them. Using these SN as input to SATIRE-T, we present the first physics- based reconstruction of total solar irradiance at annual resolution over this period.