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Mardi 6 décembre - Laminar and weakly turbulent oceanic gravity currents performing inertial oscillations

Par semsou — Dernière modification 28/11/2011 10:23
Quand ? Le 06/12/2011,
de 11:00 à 12:30
Où ? Salle Jules Vernes
Participants Achim Wirth, LEGI
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Achim Wirth, LEGI

Laminar and weakly turbulent oceanic gravity currents performing inertial oscillations

 

 

Abstract :

The small scale dynamics of a weakly turbulent oceanic gravity current is determined.

The gravity current considered is initially at rest and adjusts by performing inertial oscillations to a geostrophic mean flow.

The dynamics is explored with a hierarchy of mathematical models.

The most involved are the fully 3D Navier-Stokes equations subject to the Boussinesq approximation.

A 1D and 0D model of the same gravity current dynamics are systematically derived.

Using this hierarchy and the associated solutions of the numerical models,

the turbulent dynamics at the bottom and the interface

is explored and their interaction investigated.

Three different regimes of the small scale dynamics of the gravity current are identified,

they are characterised by laminar flow, coherent roll vortices and turbulent dynamics

with coherent streaks and bursts.

 

The problem of the rectification of the turbulent fluxes, that is how to average out the variations

and calculate their average influence on the flow is considered.

It is shown that two different regimes of friction are superposed,

an Ekman friction applies to the average geostrophic flow and a linear friction,

not influenced by rotation, to the inertial oscillations.

The combination of the two makes the bulk friction non-local in time for the 0D model.

 

The implications of the results for parametrisations of the

Ekman dynamics and the small scale turbulent fluxes in the

planetary boundary layer are discussed.

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