Wind Effects on the Buoyancy-Driven General Circulation in a Closed Basin Using a Two-Level Model

Abstract

Wind effects on buoyancy-driven circulation in a two-level rectangular basin are studied. The ocean is driven by positive and negative buoyancy fluxes in the northern and southern portions as well as wind stress of constant curl. In a model with a flat and frictionless bottom, a barotropic component is determined only by wind forcing. A baroclinic component of the wind-driven circulation, associated with horizontal density gradient, is reduced by horizontal diffusion; i.e., the wind-driven circulation is more barotropic with stronger diffusion. Meridional overturn induced by buoyancy fluxes is modified by the wind-driven circulation, for example, the southward upper-level flow, produced by positive and negative buoyancy fluxes in the northern and southern portions, greatly shifts to the western (eastern) boundary by cyclonic (anticyclonic) wind-driven circulation with realistic intensity. Relative importance of the wind-driven circulation to the buoyancy-driven circulation for meridional density transport is dependent on total Sverdrup transport of the wind-driven circulation, but independent of the buoyancy flux intensifies: the wind-driven circulation is less important with weaker wind stress and in a smaller zonal-size basin. A variable wind stress is also given, to examine effects of seasonal variabilities in wind. The results are applied to the Baffin Bay/Labrador Sea system, and suggest that the circulation pattern is changed by wind stress cud of ±10?7 N m?3. With a steady wind stress, the meridional density transport is essentially determined by the buoyancy-driven overturn. However, with the variable wind stress, the density transport varies by more than ±50%, as the system tends to adjust to the wind stress.