SOLAR DYNAMICS AND ITS IMPACT ON SOLAR IRRADIANCE AND THE TERRESTRIALCLIMATE

Among the various uncertainties present in climate modeling, the varia bility of total solar irradiance is not one of the least. For lack of any direct measure of the solar irradiance in the past, substitutes ar e needed. However, the difficulties are twofold: (1) the reliability o f the proxies and (2) the need for some physical mechanism relating th ese proxies to the solar luminosity. On the basis of a better understa nding of the solar machinery we can now propose a plausible scenario c onnecting the exchanges of energy between the various reservoirs: magn etic, thermal, gravitational, and kinetic. In the present paper we dis cuss the available proxies and suggest a way to reconstruct total sola r irradiance over the past four centuries. The response of the Laborat oire de Meteorologie Dynamique atmospheric general circulation model t o magnetoconvective solar forcing during the Maunder minimum is discus sed. The simulated cooling appears to be compatible with temperature d ata from the Little Ice Age; in addition, it is found that variations of globally homogeneous external forcing parameters, like incoming sol ar flux or greenhouse gas loading, yield climate responses with very s imilar geographical patterns.