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Accueil > Actualités > Séminaires > Séminaires 2014

Vendredi 14 novembre 2014 à 11h00 en salle A103

Benjamin Miquel, IRPHE, Marseille

Titre/Title :
Instabilities in a rotating and stratified fluid

Contact :
Nicolas Mordant

Résumé/Abstract :
Geosismic observations have revealed the stacking of horizontal layers of water
with different densities in the ocean, particularly above and beneath lens-shaped
eddies. We present a simplified model together with an experimental setup to re-
produce and identify the mechanism responsible for this layering phenomenon : we
consider the stably stratified flow around a rotating, solid ellipsoid. Experimentally,
a flat oblate rotating ellipsoid reproduces faithfully the boundary condition of an
oceanic eddy, whereas the case of a rotating sphere provides an analytically tractable
base flow, suitable for a numerical linear analysis. Two instabilities are witnessed
experimentally and numerically. The first instability is the classical, inviscid, strato-
inertial instability that tends to develop at the equator of the ellipsoid independently
of the value of the Schmidt number. The second instability is localised in the vicin-
ity of the poles and appears only if the Schmidt number differs from one. Hence,
this instability is reminiscent of the double-diffusive McIntyre instability, a valuable
candidate to explain layering in oceanic eddies.