Effects of tidal motion on the Mediterranean Sea General Circulation

The study of tides and their interactions with the complex dynamics of the Mediterranean Sea represents a crucial and important challenge in ocean modelling. In this work, the main semidiurnal and diurnal tides have been implemented in the NEMO model, with a horizontal resolution of 1/24◦, never achieved so far in this regional configuration. Both the equilibrium tide and the Atlantic tides contribute to tidal propagation in this semi-enclosed Sea. Consequently a Mediterranean Sea tidal configuration requires high resolution to solve the Strait of Gibraltar and a careful nesting on a global tidal model. On this purpose, a modelling chain is used in this work, to downscale tidal currents to the Med Sea model lateral open boundary. Tides are also very sensitive to both a reliable bathymetry and coastline, especially at the Strait of Gibraltar and to an appropriate calibration of the parameterization of the bottom friction. A barotropic- equivalent model is used to set up the configuration and to perform several sensitivity tests, then the tidal forcing is added to a complete and realistic baroclinic tidal model, which allows to study the interactions of tides with the complex dynamic of the basin. In general, modelled M2, S2, K1 and O1 waves result in good agreement with the observations. This study confirms that the interaction of the barotropic tide with the topography of the Strait of Gibraltar generates an internal tidal variability which produces an enhancement of vertical mixing at the entrance of the Mediterranean Sea. The strength of this Mediterranean tidal model is its capability to simulate from the synoptic scale to the mesoscale, an essential characteristic to understand properly the dynamics of the Mediterranean Sea and despite their moderate intensity, the important role that tides play.