Geosciences Dept. Colloquium: Inertial waves and deep ocean mixing

Abstract:

For the existing pattern of global oceanic circulation to exist there should be sufficiently strong turbulent mixing in the deep ocean. It is commonly believed that it is breaking of inertia-gravity internal waves which provides the required mixing. However this belief is not supported by understanding of why internal waves should break so intensely in the deep ocean, where they are much less energetic than in the upper ocean. The specific physical mechanisms causing the breaking have not been identified and investigated. 

The work discusses a very plausible mechanism leading to intense breaking of near inertial waves near the bottom of the ocean. The simultaneous account of both the horizontal component of the Earth rotation and its latitude dependence  (the beta-effect) reveals the existence for near inertial waves of wide waveguides attached to the bottom. These waveguides are narrowing in the poleward direction. Near inertial waves propagating poleward get trapped in these waveguides; in the process the waves are focussing more and more in the vertical direction, while simultaneously their group velocity tends to zero and wave induced vertical shear significantly increases. This results in developing of shear instability, and, hence, to wave breaking and local intensification of turbulent mixing in the deep ocean. It is showed that similarly to wind wave breaking on a beach the abyssal ocean always represents a “surf zone” for near inertial waves.

Seminar Organizer: Prof. Eyal Haifetz