On the Wind-Driven Circulation of the Uncoupled and Coupled NCAR Climate System Ocean Model

Abstract

The time-mean wind-driven circulation of the uncoupled and coupled National Center for Atmospheric Research Climate System Model ocean model is investigated. Although the coupled surface wind stress and wind stress curl magnitudes are, in general, larger than the uncoupled distributions, the coupled wind stresses are realistic, given the substantial uncertainties in the observational estimates. The Sverdrup balance, which represents a simple dynamical relation, can indeed describe the model depth-integrated transports to a large degree and shows that the increase in the coupled ocean barotropic transports is mainly due to the larger wind stress curl of the coupled system. Another simple dynamical tool, the Ekman transport analysis, shows that the coupled ocean upwelling and downwelling velocities are, in general, larger than in uncoupled ocean, consistent with the larger wind stress curl. Both models have similar upper-ocean upwelling magnitudes in the equatorial Atlantic. In the equatorial Pacific, the coupled ocean upwelling is much larger. The coupled ocean surface currents, similarly stronger than in uncoupled ocean, differ from the uncoupled currents especially in the Nordic Seas. The Ekman transport contribution to the northward heat transport is significant in the tropical regions and in the Southern Hemisphere midlatitudes, and this transport is larger in coupled ocean than in uncoupled ocean.