Dynamique et stabilité de fronts : phénomènes agéostrophiques

Abstract : This thesis has to be seen within the general study of atmospheric and oceanic fronts and the origin of gravity waves in the atmosphere. In this context we focus on a front in a rotating two-layer miscible fluid under vertical shear. Both experimental and numerical study highlights ageostrophic phenomena going beyond the usual geostrophic equilibrated configuration of a baroclinic front. First, the classification of different instability regimes of a front in an annular configuration as a fonction of Rossby number and Burger number reveals an ageostrophic instability coupling equilibrated and divergent motions due to a resonance between a Rossby wave and a Kelvin wave. This Rossby-Kelvin instability is confirmed numerically by the structure of the perturbation velocity fields in each layer. Second, small-scale structures have also been observed experimentally. Caracteristics of the interface in function of Richardson number and density and velocity interface thicknesses suggests the presence of the Hölmböe shear instability. A direct numerical simulation with an axisymmetric configuration and with a Schmidt number 700 confirms this conjecture. Other smalle-scale perturbations compatible with inertia-gravity waves have been observed numerically superimposed on an unstable Rossby-Kelvin front and the wave generation mechanism is discussed. In addition, a numerical study of a stable front highlighted the presenec of internal Ekman layers with an additional interfacial structure in the case of high Schmidt number and small Rossby number. For fronts in in/outcropping, front dynamics is modified by interaction with Ekman boundary layer at the location of the intersection zero-thickness singular point. It depends on both vertical circulation and mixing on the nose of the front and the various possible instabilities associated to horizontal or vertical wave resonances.
Document type :
Complete list of metadatas

Contributor : Abes Star <>
Submitted on : Monday, March 9, 2015 - 11:04:43 AM
Last modification on : Tuesday, May 21, 2019 - 9:23:28 PM
Long-term archiving on : Wednesday, June 10, 2015 - 1:25:13 PM


Version validated by the jury (STAR)


  • HAL Id : tel-01128054, version 1




Hélène Scolan. Dynamique et stabilité de fronts : phénomènes agéostrophiques. Sciences de la Terre. Université Grenoble Alpes, 2011. Français. ⟨NNT : 2011GRENU039⟩. ⟨tel-01128054⟩



Record views


Files downloads