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Accueil > Actualités > Séminaires > Séminaires 2016

Mardi 14 juin 2016 à 11h00 en salle K118

Catherine.Vreugdenhil et Ross Griffiths, Research School of Earth Sciences, ANU College of Physical & Mathematical Sciences, Canberra, Australie

Titre/Title : Adding turbulent convection to a geostrophic circulation : rotating horizontal convection

Contact : Jan-Bert Flor (équipe MEIGE)

Résumé/Abstract : Large scale and quasi-horizontal components of ocean circulation are geostrophically balanced. However, the circulation is partially forced by convection due to surface buoyancy fluxes, and convection involves essential ageostrophic and vertical motion. The convection is at small scales in the surface convecting layer, at mesoscales in regions of high latitude deep convection, as well as at the global scale where it is manifest as a contribution to the Meridional Overturning Circulation and, likely, to the horizontal gyre circulations and Antarctic Circumpolar Current. The ocean is characterised by extremely large Rayleigh numbers at which convection is expected to be turbulent. Ocean models resolve only the geostrophic large- and (sometimes) meso-scales, and rely on sub-grid parameterisations to include convection, turbulence and Ekman layers. Here we examine an idealised model system, with circulation in a rotating rectangular basin forced by a gradient of surface buoyancy conditions (termed horizontal convection), using both laboratory experiments and Direct Numerical Simulations. We take the system to large Rayleigh numbers at which the thermal boundary layer is turbulent while having a geostrophic mean flow. The convection, turbulence and Ekman layers are fully resolved by the DNS. Although this limits us to Rayleigh numbers much smaller than for an ocean basin, much can be learned about dynamical regimes and the role of convection.