LES Modelling of the Impact of the Topography on Large-scale Exchange Flow in the Strait of Gibraltar

The Mediterranean Sea is connected to the North Atlantic basin by the Strait of Gibraltar, a narrow and shallow passage. The entry of Atlantic water at the surface compensates the net evaporation over the whole Mediterranean Sea, as well as the evacuation of intermediate and deep Mediterranean waters through the Strait. The topography of the strait has a strong impact on the exchange flow: large-scale circulation and tidal currents induce indeed an hydraulic control leading to primary instabilities and large-amplitude internal waves in the wake of the many sills.

The complex sequence of topographycally-induced small-scale processes is explicitly simulated with a nested, LES, 50-m-resolution implementation of the non-hydrostatic, free-surface, CROCO model. Consequences of small-scale processes on large-scale flow are detailed and a special attention is paid to the space-time variability of internal jumps, primary instabilities, internal bores and internal solitary waves in order to prepare the Gibraltar 2020 in-situ campaign. The impact of the numerical schemes are carefully studied in this novel LES modelling.