ROLE OF THE OCEANIC HEAT-TRANSPORT IN CLIMATE DYNAMICS - A SENSITIVITY STUDY WITH AN ATMOSPHERIC GENERAL-CIRCULATION MODEL

Estimating meridional ocean heat transport from the present generation of atmospheric general circulation models, assuming energetic equilib rium, leads to a large variety of results, depending on the model. The current uncertainty on such an important process may cause significan t errors in coupled atmosphere/ocean models. To determine the possible nature of these errors, investigate how the prescription of the ocean ic heat transport can affect the results of a coupled surface ocean/at mosphere model where the ocean is limited to thermodynamics and turbul ent fluxes but sea-ice is included. In particular, we study the respon se of the surface fluxes and atmospheric transport to a reduction of t he ocean transport. We focus on the initial phase, where these feedbac k effects begin to develop while the model is still realistic. The mod el response is strongly dependent on a combination of features: change s in the Hadley cell circulation, the atmospheric heat transport, the radiative and turbulent fluxes at the surface, changes of the radiativ e fluxes at the top of the atmosphere. In this study, we examine the p artitioning between these different effects. It is shown that the atmo sphere partly takes up the missing ocean transport, but that this lead s to a change in the cloud/radiative equilibrium of the ITCZ region.