An unsteady wind-driven ocean circulation model

This model of a continuously stratified ocean, consisting of surface Ekman and thermal layers and a deep abyssal region, is driven by an unsteady surface wind stress. The model yields a nonlinear planetary wave equation for the surface temperature which is solved by the method of characteristics. Horizontal distributions of the surface temperature, the heat content and the potential energy are computed. For a model zonal wind stress relevant to the North Atlantic, a parameter sensitivity study is made.Long time scale observations of the heat content in the North Atlantic north of 45°N show that periods of heating and cooling of a few decades duration frequently occur. Using a zonal wind stress consisting of the superposition of a mean and two time harmonic components, secular variations in the surface temperature field manifest themselves as a beat period, provided the time harmonic frequencies are close together. Finally, to investigate the effects on the circulation produced by the changing intensity of the westerly winds, numerical results are presented for the case when the wind stress distribution oscillates in the north-south direction with time. Results from the study show that the heating and cooling periods of a few decades duration in the North Atlantic can be reproduced.