Samuel Viboud

Quantitative laboratory observations of internal wave reflection on ascending slopes

Internal waves propagate obliquely through a stratified fluid with an angle that is fixed with respect to gravity. Upon reflection on a sloping bed, striking phenomena are expected to occur close to the slope. We present here laboratory observations at moderately large Reynolds number. A particle image velocimetry technique is used to provide time-resolved velocity fields in large volumes. Generation of the second and third harmonic frequencies is clearly demonstrated in the impact zone. The mechanism for nonlinear wavelength selection is also discussed. Evanescent waves with frequency larger than the Brunt-Vaisala frequency are detected and experimental results agree very well with theoretical predictions. The amplitude of the different harmonics after reflection is also obtained.

A laboratory study of low-mode internal tide scattering by finite-amplitude topography

We present the first laboratory experimental results concerning the scattering of a low-mode internal tide by finite-amplitude Gaussian topography. Experiments performed at the Coriolis Platform in Grenoble used a recently conceived internal wave generator as a means of producing a high-quality mode-1 wave field. The evolution of the wave field in the absence and presence of a Gaussian was studied by performing spatiotemporal modal decompositions of velocity field data obtained using particle image velocimetry. The results support the belief that finite-amplitude topography produces significant reflection of the internal tide and transfer of energy from low to high modes.