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BIRS Workshop Lecture Videos

Energy Cascade in Internal Wave Attractors Dauxois, Thierry


Internal gravity waves play a primary role in geophysical fluids : they contribute significantly to mixing in the ocean and they redistribute energy and momentum in the middle atmosphere. In addition to their very interesting and very unusual theoretical properties, these waves are linked to one of the important questions in the dynamics of the oceans: the cascade of mechanical energy in the abyss and its contribution to mixing. I will discuss a setup that allows us to study experimentally the interaction of nonlinear internal waves in a stratified fluid confined in a trapezoidal tank. The set-up has been designed to produce internal wave turbulence from monochromatic and polychromatic forcing through three processes. The first is a linear transfer in wavelength obtained by wave reflection on inclined slopes, leading to an internal wave attractor which has a broad wavenumber spectrum. Second is the broad banded time-frequency spectrum of the trapezoidal geometry, as shown by the impulse response of the system. The third one is a nonlinear transfer in frequencies and wavevectors via triadic interactions, which results at large forcing amplitudes in a power law decay of the wavenumber power spectrum. This first experimental spectrum of internal wave turbulence displays a $k^{-3}$ behavior.

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