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Abstract

An ocean basin of uniform depth is considered. It is bounded laterally by two meridians. Temperature and wind stress are specified as functions of latitude at the upper surface. The physical model is similar to that used in previous models of the oceanic thermocline, except that the momentum equations of the horizontal velocity components are retained in nearly complete form. Solutions are obtained by the direct numerical integration of a corresponding initial value problem using an electronic computer. Dimensional analysis indicates that the system depends on 5 basic parameters. The geophysically significant range of these parameters is investigated in 8 numerical experiments.

Computations with and without wind stress show the interaction of the thermohaline and the wind-driven components of the large scale circulation. Without wind a single large anticyclonic gyre extends over the entire surface of the basin. There is a shallow western boundary current, extending to high latitudes, and a vertically uniform southward drift in the interior from the surface down to the base of the thermocline. A sluggish cyclonic gyre exists below the thermocline. The addition of a wind stress pattern corresponding to a maximum in the westerlies at 45°N leads to the formation of an additional cyclonic gyre in subarctic latitudes. In spite of the simplified boundary conditions the solutions with wind stress reproduce many details of the observed density structure in the North Atlantic, particularly in the subtropical gyre.

A more quantitative comparison with North Atlantic data indicates that a choice of the vertical diffusion coefficient, ℵ, to be 1 cm2/s gives an approximate fit to the thermocline depth and estimates of the total poleward transport of heat. The corresponding renewal time for deep water, however, is considerably less than that indicated by C14 data.