Generation of harmonics and sub-harmonics from an internal tide in a uniformly stratified fluid: numerical and laboratory experiments

This paper focuses on the internal tide emitted from a continental slope in a uniformly stratified fluid. Results from numerical simulations using the MITgcm and from laboratory experiments performed on the Coriolis platform in Grenoble are compared. Due to their peculiar dispersion relation, internal gravity waves organize into localized beams of energy. We show that the beam structure is well-predicted by the viscous theory of (Hurley and Keady, 1997), assuming that the internal gravity wave field is emitted by a horizontally oscillating cylinder whose radius is the radius of curvature of the topography at the beam emission. The wave beam can bear a sub-harmonic parametric instability whose vertical scale is recovered from resonant interaction theory. Reflection of the wave beam on the bottom leads to the generation of harmonic beams, consisting of free and trapped waves.