General circulation and intergyre dynamics in the eastern North Atlantic from a regional primitive equation model

Abstract

The mean circulation of the eastern North Atlantic is investigated using a regional 0.8° x cos(latitude)-resolution configuration of the SPEM primitive equation sigma coordinate model, forced by seasonal and monthly surface fluxes. The computational domain is surrounded by three self-adapting open boundaries which evacuate the outgoing perturbations and laterally control the baroclinic modes in inflow regions, but let the model adjust the barotropic mode to a large extent. The final solution is stable and reproduces most features of the basin's mean circulation well: A realistic Azores Current, the observed paths and transports of subpolar currents, of the branches of the North Atlantic Current, of the intergyre zone modal and intermediate water masses down to about 2000 m. Some unrealistic circulation features, attributed to the modest resolution and to certain limitations of the sigma coordinates, are found below 2000 m. The buoyancy and vorticity balances are investigated in the intergyre zone. The Subpolar Mode Water (SPMW), subducted at a realistic rate, continues its southward journey toward the ocean's interior in accordance with the ventilated thermocline theory, with eddy diapycnal fluxes exerting a moderating effect. The poleward motion observed between 300 and 1000 m is well reproduced north of 45° N and governed by similar dynamics, but is absent south of 45° N within the upper Mediterranean Water. Copyright 2001 by the American Geophysical Union.