The interaction of tidal currents with ocean bottom topography results in the radiation of internal gravity waves into the ocean interior. These waves are called internal tides and their dissipation due to nonlinear wave breaking could play an important role in the mixing of the abyssal ocean, and hence in controlling the large-scale ocean circulation.
We investigate internal waves generated
by oscillating obstacles of different idealized geometries as a model of ocean topography, and consider linear as well as nonlinear
wave effects of waves emitted by these obstacles and wave-wave interactions.
Wave focusing may be generated in geophysical flows due to particular topographic geometry. Focusing of internal waves in a linearly stratified fluid is investigated experimentally for waves generated by horizontal oscillation of a torus. Internal waves are measured via Particle Image Velocimetry in order to obtain the both vertical and horizontal velocity components. For symmetric waves, generated by the oscillation of the torus, it is shown that the wave amplitude is two times larger in the focal region than close to the surface of the torus, leading to local nonlinear wave amplification. Subsequent overturning is observed in the focal region for large oscillation amplitude of the torus. Second harmonic waves emanating from the intersection of the first-harmonic beams are obtained. These experiments show that the focusing of internal waves may lead to overturning even for low wave energy, and therefore can be an effective mechanism for the generation of abyssal mixing.