Historical solar variability derived from sunspot areas using a FIR model

Abstract

We present new historical reconstructions since 1875 of several parameters of solar variability of interest for climate modeling, including spectral solar irradiance at ultraviolet wavelengths and average magnetic field. The reconstructions are based on our Finite Impulse Response (FIR) model, presented in previous work, which establishes the detailed relationship between observed solar variability and sunspots. This model predicts very little long‐term secular trend in the level of solar minimum for any of the reconstructed solar parameters. Cycle‐averaged spectral solar irradiance at ultraviolet and extreme ultraviolet wavelengths increases by about 3% and 20%, respectively, during the first half of the twentieth century. The corresponding cycle‐averaged change in the average magnetic field is about 50%. We estimate that from the Maunder Minimum to the present, the cycle‐averaged increase is about 4% for the irradiance at 200 nm, 30% for the irradiance at 121.6 nm and 100% for the average magnetic field.