Dense overflow over a continental slope in a rotating environment

(thesis S. Décamp)

Dense overflows are of particular interest as they play an important role in the global thermohaline circulation. Both experimental and numerical modelisations of dense gravity currents on a slopping bottom under the influence of the Coriolis force are studied, in either homogeneous or uniformly stratified environment. In the Atlantic ocean, this configuration resemble for example the descent of cold water coming from polar oceans, or high salimity flows from the mediterranean sea.
Experiments are performed on the Coriolis turntable. The large dimension of the experiment allows good similarity with the oceanic scale. High resolution measurements of velocity are obtained by PIV (Particle Image Velocimetry) on fields of 1.8m x 1.8m.
Numerical simulations are made using MICOM (Miami Isopycnic Coordinate Model).

Dense fluid is injected through an horizontal channel, flows down the slope under the influence of gravity, with intense turbulent mixing occuring at the interface. The rotation deflects the current and the flow is stabilized into a geostrophically balanced jet along the slope.

Picture of the experiment (click to enlarge):

The aim is to determine experimentaly the depth of stabilization of the main current, its width and thickness, to measure the turbulent mixing and to observe the instabilities created (like eddies formation) from density profiles and velocity fields. Experimental results are compared with numerical simulations, and are used to test the ability of an isopycnal model to simulate dense water overflows on a slope. The turbulent parameterization, the influence of mixing and diapycnal entrainment still have to be tested.