Modelling irradiance variations from the surface distribution of the solarmagnetic field

An important question in solar physics is to what extent solar surface magn etism affects the solar irradiance. Previous attempts to answer this questi on have employed proxies of the magnetic field to reconstruct the irradianc e and compare it with observations. Here we present the first model calcula tions of solar irradiance variations based on variations of the surface dis tribution 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 t he solar disk are extracted from full-disk magnetograms obtained by the Mic helson Doppler Interferometer (MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance variations are compared with total an d spectral contrast measurements obtained by the VIRGO instrument onboard S OHO. Our reconstructions are able to reproduce variations on the time-scale of the solar rotation with much greater accuracy than previous models base d on disk-integrated magnetic proxies.