Centennial Total Solar Irradiance Variation

Total Solar Irradiance (TSI) quantifies the solar energy received by the Earth and therefore is of direct relevance for a possible solar influence on climate change on Earth. We analyse the TSI space measurements from 1991 to 2021, and we derive a regression model that reproduces the measured daily TSI variations with a Root Mean Square Error (RMSE) of 0.17 W/m(2). The daily TSI regression model uses the MgII core to wing ratio as a facular brightening proxy and the Photometric Sunspot Index (PSI) as a measure of sunspot darkening. We reconstruct the annual mean TSI backwards to 1700 based on the Sunspot Number (SN), calibrated on the space measurements with an RMSE of 0.086 W/m(2). The analysis of the 11 year running mean TSI reconstruction confirms the existence of a 105 year Gleissberg cycle. The TSI level of the current grand minimum is only about 0.15 W/m(2) higher than the TSI level of the grand minimum in the beginning of the 18th century.

Automated summary

This study analyzed the space measurements of Total Solar Irradiance (TSI) and derived a regression model to reproduce the daily variations of TSI. The reconstruction of TSI based on the Sunspot Number confirmed the existence of a 105-year Gleissberg cycle, with the TSI level of the current grand minimum only slightly higher than that of the 18th century.