A sensitivity study of the general circulation of the Western Mediterranean Sea. Part I: The response to density forcing through the straits

In this paper, the influence of the density gradients at the straits of Gibraltar and Sicily on the large-scale circulation of the Western Mediterranean Sea is investigated through a 3D numerical model. The topography constraint is analyzed by comparing an experiment with a flat bottom with an experiment with a realistic bathymetry. The results show the ability of the density gradients at the straits to force a cyclonic surface circulation in the whole basin, particularly in the northern basin where the transport in the Liguro-Provençal current is about 40% of the observed one. These experiments point out the key role played by the strait of Sicily and its topography. There the eastward surface flow separates into two branches: one enters the Eastern Mediterranean Sea, while the other flows along the Italian coasts to feed the cyclonic circulation of the northern basin. In the Alboran Sea, which is a priori the region where the dynamics is the most strongly induced by the transport through the Strait of Gibraltar, the circulation is quite well reproduced. These experiments also reproduce the instability of the Algerian Current and confirm that the baroclinic instability seems to be the source of the meandering of the current.