Numerical Study of the Mediterranean Outflow with a Simplified Topography

Abstract

A 3D numerical model is used to setup a simplified scenario on the Atlantic side of the Strait of Gibraltar. This scenario simulates the surface and a Mediterranean Outflow Water (MOW) escaping to the Atlantic near the sea bottom. The MOW has two different main paths: northwards, along the Iberian slope, reaching as far as the Scandinavian Peninsula, thereby influencing the formation of North Atlantic Deep Water (NADW), and southwestwards propagating into the Atlantic Ocean. In this simplified scenario we want to study the way a gravity current, like the MOW, behaves for different outflow conditions. The emphasis is on understanding how distinct outflow conditions lead to different propagating depths and mixing that may affect NADW formation under predicted global change future scenarios. The ROMS model domain is centered in the area of the Gulf of Cadis. The northern and southern boundaries are delimitated by the Iberian Peninsula and the Moroccan coast, while the eastern boundary is at 6ºW, near the Camarinal Sill, and the western boundary is open, reaching as far as Cape San Vicente. The imposed boundary conditions consist in two layers of different density, the upper one simulating the AW and the lower simulating the MOW. The grid has 96 X 64 grid points with a resolution of about 3 km and 36 sigma levels. The complex topography of the area is simplified through a slope with two different zonal dependences: the initial (1/3 of the domain) decay of the bathymetry at the east is adjusted by a hyperbolic tangent function, followed by a constant slope. Initial conditions are setup as follows. The western part of the basin is filled with AW, and the eastern part of the domain is filled with AW from the surface to 150 m and with MOW from 150 m to the sea bottom. The open boundary conditions for temperature, salinity and velocity are specified using climatological vertical profiles. In particular, the velocity profiles have been adjusted and calculated with a positive velocity for the inflow and negative one for the outflow, such that mass is conserved within the model domain. Forcing conditions are setup with winds and atmospheric pressure fields