The Impact of Surface Flux

The response of an ocean general circulation model to several distinct parameterizations of the surface heat and fresh water uxes, which di er primarily by their representation of the oceanatmosphere feedbacks, is investigated in a realistic con guration for the North Atlantic Ocean. First, the impact of explicitly introducing oceanic information (climatological sea surface temperature) into the computation of the heat ux through a Haney-type restoring boundary condition, as opposed to the case in which the ux is based on atmosphere-only climatologies and is computed with the full bulk formulation, is considered. The strong similarity between these two approaches is demonstrated, and the sources of possible di erences are discussed. When restoring boundary conditions are applied to the surface salinity, however, an unphysical feedback mechanism is being introduced. The model's response to this restoring is contrasted to the response to a ux boundary condition that prescribes the fresh water ux derived from evaporation, precipitation, and river runo climatologies (and therefore does not allow any feedback), as well as to the more realistic case in terms of the feedback parameterization, in which the dependence of evaporation on the model sea surface temperature is explicitly represented. Limited area models introduce a further complicating factor for the thermodynamic adjustment, namely the representation of the oceanic heat and fresh water uxes at the lateral boundaries. The degree to which the model solution is in uenced by such uxes, in combination with the di erent surface parameterizations, is also assessed. In all cases, the various components of the model's thermodynamic adjustment are considered, and the interdependence between the surface uxes and the simulated sea surface temperature and surface salinity, their combined e ect upon the ventilation of subsurface layers and production of di erent water masses, and their e ect upon the simulated meridional heat and fresh water transports are analyzed.