CONVECTIVE FLOW PATTERNS IN AN 8-BOX CUBE DRIVEN BY COMBINED WIND STRESS, THERMAL, AND SALINE FORCING

An eight-box cube model ocean, simulating the subpolar gyre in the North Atlantic, is formulated in order to understand how the wind-induced horizontal gyre affects the thermohaline circulation and its catastrophe. The model is forced from above by thermal conduction and freshwater flux. The structure of the thermohaline circulation and its catastrophe during the process of gradually increasing or reducing the evaporation/precipitation are examined. The results indicate that, although adding the third dimension and a wind-driven horizontal gyre of medium strength splits the catastrophe into several separate ones, only some of these catastrophes remain of significant amplitude. With choice of parameters appropriate for the North Atlantic, the model predicts a single stable state, circulating in the thermal sense (sinking at the pole). This can be driven smoothly to a reversed saline sense (sinking at the equator), without catastrophe, by increasing the precipitation/evaporation rate beyond 3 times the present-day value.