Separation of a Coastal Current at a Strait Level: Case of the Strait of Sicily

The separation of a coastal current into two branches when encountering a strait, one entering the strait and the other crossing the strait and continuing to flow along the coast, is examined. Analytical solution shows that the strait topography plays a major role in the separation. When the depth of the sill of the strait is shallower than the ocean, double Kelvin waves propagate along the sill discontinuity line and are able to transport energy across the strait. The shallower the sill, the smaller the transport of the surface current entering the strait at the upstream corner and the larger the transport of the current transmitted across the strait. Sensitivity experiments done with a high-resolution primitive equation model confirm this behavior. These considerations explain the separation of the Algerian current into two branches at the Strait of Sicily: one entering the Eastern Mediterranean Sea and the other flowing into the Tyrrhenian Sea.