NONLINEAR ROSSBY WAVES IN A THERMODYNAMIC REDUCED GRAVITY OCEAN

A single active layer thermodynamic reduced gravity upper ocean circulation model is presented. The model is forced by prescribed surface heat flux (via the air temperature distribution) and wind stress and describes motions on the season to inter-annual time scale, with horizontal length scales of the order of 1000 km. The model is applied to a domain typical of the North Atlantic between 25 -N to 45 -N. Steady solutions are calculated and are used to initialise the time dependent model. The latter is used to calculate the upper ocean response to either (a) a reduction of the zonal wind stress magnitude by 50% over several days, (b) meridional oscillations of a zonal wind stress, (c) annual and inter-annual fluctuations of the net heat flux through the sea surface and (d) temperature fluctuations along the ocean-edge of the Gulf Stream associated with seasonal variability of the transport of the current. Rossby wave propagation is identified in cases (a) to (c) and the waves play a major role in the upper ocean variability. In case (d) the model develops and sheds a warm eddy into the ocean interior. © 1990, Taylor & Francis Group, LLC. All rights reserved.