Titre/Title :
Evolution of near-inertial waves in the ocean
Contact :
Chantal Staquet (Equipe Eres)
Résumé/Abstract :
For the existing pattern of global oceanic circulation to exist there should be sufficiently strong turbulent mixing in the abyssal ocean. It is commonly believed that it is breaking of inertia-gravity internal waves which somehow provides the required mixing. However this belief is not supported by understanding of why internal waves should break intensively in the abyssal ocean. The specific physical mechanisms causing the breaking have not been identified and investigated.
We discuss a very plausible mechanism leading to intense breaking of near inertial waves near the bottom of the ocean. Mathematically the challenging problem of inertia-gravity wave evolution in the arbitrary density stratified ocean on the sphere is considered analytically. The simultaneous account of both the horizontal component of the Earth rotation and its latitude dependence (the beta-effect) reveals the existence of several waveguides for near inertial waves, with the widest waveguide attached to the bottom of the ocean. These waveguides are narrowing in the poleward direction. Near inertial waves propagating poleward are trapped in these waveguides; become more and more focussed in the vertical direction in the process, while their group velocity tends to zero. Correspondingly the wave induced vertical shear significantly increases. This results in developing of shear instability, and, hence, to wave breaking and intensification of turbulent mixing in the abyssal ocean. It is shown that similarly to wind wave breaking on a beach the abyssal ocean always represents a surf zone for near inertial waves.