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Home > News > Ph.D. Thesis > Ph.D. Thesis 2015

Jeudi 2 avril 2015, soutenance de thèse de Pïerre LABREUCHE - 13h30, Amphithéâtre K118, site Bergès ENSE3

Internal lee waves in the abyssal ocean: diapycnal mixing and interactions with inertial oscillations

Thesis supervisor

- M Julien Lesommer,
Research Officer, CNRS, Supervisor
- Mme Chantal Staquet,
Professor, UJF, Supervisor

Abstract

The Southern Ocean plays a key role in global ocean circulation by connecting the major ocean basins with the intense Antarctic Circumpolar Current and as a formation region for abyssal water masses of the global ocean. Understanding the diapycnal mixing processes that link these abyssal waters to the overlying layers is essential both for ocean modelling and for predicting future climate change.

In the Southern Ocean, deep reaching currents impinge on rough topography and create highly energetic internal lee waves. The dissipation of the energy of these internal lee waves is the main candidate for explaining the high mixing rates between waters of different densities observed at these latitudes. The purpose of this study is to understand the fate of the internal lee wav energy and how it affects the circulation and diapycnal mixing in the abyssal ocean.

We first study the impact of internal lee waves on deep mixing with the combination of field expertise, two-dimensional non hydrostatic numerical simulations and theoretical developments. Over the range of parameters studied, an enhanced bottom turbulent kinetic energy dissipation is observed in the bottom 1000 m, typically reaching ∼ 20 mW/m2. We further show that internal lee waves undergo non-dissipative wave-wave interactions that can be rationalized as resonant triad interactions between the bottom emitted internal lee waves, inertial oscillations and linear combinations of these two waves.

We then build a three-dimensional model configuration and specific diagnostic methods that pave the way for future investigations in three dimensions. Preliminary results with the threedimensional numerical configuration show that the meridional confinement of the topography notably reduces the emission of internal lee waves.

Keywords

Oceanography, internal lee waves, diapycnal mixing, dissipation of turbulent kinetic energy, wave-wave interactions, wave-mean flow interactions