Effects of tidally driven mixing on the general circulation in the ocean model MPIOM.

A mixing parameterization, which produces spatial variations of diapycnal diffusivity depending on the locations of tidal energy dissipation over rough topography, is implemented in the MPI-Ocean Model. A simulation with this mixing parameterization is compared with two control experiments using the standard configuration, each one with different spatially constant background diffusivity. The diffusivity in the first experiment is strong above rough topography and weak over smooth regions. The experiment with tidal mixing reduces density bias and improves representation of the water masses. The deep enhanced mixing due to tides increases the deep and bottom circulation in the Pacific Ocean, and produces stronger western boundary currents. The Atlantic circulation is sensitive to tidal mixing, and the differences with the control runs are significant, but not dramatic. Tidal mixing induces stronger horizontal gradients of the deep and bottom water properties which, in turn, are responsible for the increase of the mass transport through the Drake ∗Corresponding author. Address: Bundestrasse 53, 20146 Hamburg, Germany. Tel.:+49 40 411 73 181 Email address: eleftheria.exarchou@zmaw.de (E. Exarchou) Preprint submitted to Ocean Modelling June 2, 2010 Passage. Regional effects of tidal mixing are also investigated. Significant changes are observed in the Nordic Seas: the tidal run produces 0.3-0.7 Sv larger overflows than the two control runs. The results of the stronger overflows in the Nordic Seas and the stronger circulation in the Pacific Ocean are more comparable with the observations, and underline the importance of using a spatially variable diapycnal mixing for more realistic and physically based simulations.

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