The impact of solar forcing on the variability in a coupled climate model

The impact of variations in solar irradiance on the variability of climate is still a topic of debate. Herein we assess the response of a coupled General Circulation Model (GCM) of intermediate complexity to an estimate of the solar variability since 1700 and to a series of idealized sinusoidal solar forcings. On the continental to global scale and averaged over periods longer than 30 years, the solar-induced variability dominates internal variability in the annual global mean surface air temperature. Locally and on the regional scale, the internal variability dominates. The dominant patterns of natural variability and explained variance are not affected by a variable solar forcing, the spectra however are sensitive. The control run shows a preferred decadal time scale of 18 year in a sea surface temperature mode associated with the North Atlantic Oscillation. The preferred decadal time scale disappears for a variable solar forcing. This is caused by small changes in oceanic circulation resulting in subsurface oceanic modes with modified structure and time scale.