Modelling irradiance variations from the surface distribution of the solar magnetic field

Abstract

An important question in solar physics is to what extent solar surface magnetism affects the solar irradiance. Previous attempts to answer this question have employed proxies of the magnetic field to reconstruct the irradiance and compare it with observations. Here we present the first model calculations of solar irradiance variations based on variations of the surface distribution of the solar magnetic field. The irradiance reconstruction makes use of sunspot and facular contrasts calculated as a function of wavelength and limb angle on the Sun. The position and size of magnetic features on the solar disk are extracted from full-disk magnetograms obtained by the Michelson Doppler Interferometer (MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance variations are compared with total and spectral contrast measurements obtained by the VIRGO instrument onboard SOHO. Our reconstructions are able to reproduce variations on the time-scale of the solar rotation with much greater accuracy than previous models based on disk-integrated magnetic proxies.