Interaction of a coastal current with a gulf: Application to the shelf circulation of the Gulf of Lions in the Mediterranean Sea

The interaction of a coastal current with a shallow shelf is studied using analytical model and numerical simulations. First, the wave propagations along a steplike bottom topography in a two-layer fluid are investigated. The authors focus on the case in which the interface between the two layers is deeper than the shelf depth and show analytically that two waves propagate along the shelf break: one is represented by a barotropic/baroclinic double Kelvin wave, the other by a baroclinic wave trapped at the shelf break. The velocity of the latter is proportional to the difference between the depth of the shelf and the depth of the upper layer off the shelf. A primitive equation model was also used to study more realistic configurations 1) with an idealized shallow gulf and 2) with a realistic topography like that of the Gulf of Lions. It is shown that the steady component of the coastal current follows the shelf break. A transient cross-shelf transport can be induced by a gulf-scale gyre associated with the current variation. These results are also valid in the case of a buoyant current penetrating onto the shelf.