Simultaneous velocity and density measurements for an energy-based approach to internal waves generated over a ridge
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We present experimental results of internal wave generation by the oscillation of a two-dimensional topography in a linearly stratified fluid. Simultaneous synthetic schlieren and particle image velocimetry high-resolution measurements are made in a series of experiments with different forcing frequencies, all other parameters being kept constant. This setup allows us to obtain the potential and kinetic components of the mechanical energy transported by the internal wave beam for different relative values of the maximum topographic slope to the slope of internal wave phase lines, in a quasi-linear regime. Measurements are carefully validated and a combined wavelet and principal component analysis are carried out to extract the most energetic physical processes associated with the internal waves. The duration of the transient regime is evaluated in order to consider only results during the steady regime. We discuss the evolution of the radiated mechanical energy with respect to the forcing frequency, and we show that it reaches a maximum in the near-critical regime, in good agreement with recent numerical and theoretical works. New insights are provided about the role played by the relative values of the maximum topographic slope and the internal wave beam slope in the efficiency of energy transfers from barotropic tide to radiated internal waves. This study is a step toward a better quantification of the energy transported away by internal waves and available for mixing the ocean.
This work has been supported by LEFE-IDAO Program “ondes et marées interne dans l’océan” (LEFE-IDAO-07/29) and ANR “TOPOGI-3D” contract (ANR-05-BLAN-0176). We thank B. Beaudoin, A. Belleudy, J.-C. Boulay, B. Bourdelles, J.-C. Canonici, S. Lassus-Pigat, F. Murguet, M. Morera, and H. Schaffner of the CNRM-GAME (URA1357, METEO-FRANCE and CNRS) fluid mechanics laboratory, as well as J. Gil for their kind support during the experiments. We also wish to thank F. Pétrélis for helpful discussions as well as R. Montroty.
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