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Mixing in continuously stratified flow over a topographic ridge

Yvan Dossmann (Laboratoire de Physique, ENS de Lyon)
Quand ? Le 24/02/2015,
de 10:45 à 12:00
Où ? Centre Blaise Pascal
Participants Yvan Dossmann
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The dynamics of turbulent mixing of a uniformly stratified fluid over a two-dimensional ridge is investigated in laboratory experiments. The roles of variables such as the upstream buoyancy frequency, flow speed and the ridge shape are examined. A light attenuation technique is used to obtain high-precision density measurements and perturbations to isopycnals, from which we quantify and the amount of irreversible turbulent mixing. Two main dynamical features are observed: a local, turbulent flow in the wake and slightly above the ridge, and the radiation of internal lee waves. The ratio, q, of these local and remote contributions to mixing is calculated and takes an average value q = 90 +/-  6%. This is three times larger than the canonical value q = 30 +/- 10% that is commonly assumed in parameterizations of internal wave-induced mixing in the ocean. This result may help to assess the importance of local non-linear processes for mixing the deep ocean.

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