Ondes internes générées sur une dorsale océanique : du laboratoire à l'océan

Abstract : Internal tides are involved in the Meridional Overturning Circulation energy balance. The ongoing debate on the relative importance of the mechanical and thermodynamical energy sources emphasizes the need for quantitative energy transfers evaluations. A complementary approach relying on numerical and experimental tools is adopted to describe the generation of internal waves over a topography in various regimes of linearity and stratication, inspired by oceanic configurations. First, an energy-based experimental study of linear internal waves generation by the oscillation of a Gaussian ridge in a linearly stratied uid is performed. The mechanical energy evolution permits to highlight that near-critical bottom topographies are likelier to generate powerful internal waves. The dynamics of topographic internal solitary waves (ISW)generated in regions of important density gradients, such as the ocean pycnocline, is then studied. These waves are responsible for important energy transfers, as they initiate turbulent mixing while they propagate in the pycnocline. Simulations using the numerical model Symphonie-NH are performed to describe two generation processes observed in the ocean. I rst focus on the ISW primary generation, caused by the direct interaction between the barotropic tide with the ocean bottom topography,observed in strong pycnocline regimes in the ocean, such as in the Sulu sea. The structure of internal solitary waves is compared with simple analytical models such as the KdV scheme. By changing the ridge geometry, a strong topographic control, described by a simple nondimensional parameter, is observed in the ISW primary generation process. Afterwards, the secondary generation of internal solitary waves, induced by the interaction between internal wave rays emitted at a topography and a pycnocline of moderate strength, like in the Bay of Biscay, is treated. Direct numerical simulations are performed to study the dynamics of these internal solitary waves, and their damping due to a downward leaking of energy. The evolution of the normal modes structure with respect to the pycnocline strength, as well as the role played by the topography shape are described in order to provide new insights regarding the secondary generation process. Experiments are performed to study the primary and secondary generations of internal solitary waves in the large water tank of CNRM-GAME. An experimental configuration using a steep sinusoidal ridge oscillating in a two-layer uid is used. Measurements with ultrasonic probes and optical measurements permit to observe the dynamics and the 3D structure of these waves. ISW issued from the primary generation process appear more stable than in the secondary generation process, for which substantial transverse structures are observed.
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Submitted on : Wednesday, November 28, 2012 - 12:42:55 PM
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Yvan Dossmann. Ondes internes générées sur une dorsale océanique : du laboratoire à l'océan. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2012. Français. ⟨tel-00758207⟩

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