Mass transport generated by stratified internal wave boundary layers

Abstract

Internal waves, generated by tidal oscillations over rough bottom topography at the margins of shallow seas, are known to be important for the mixing budget of the ocean. One of the open questions in the dynamics of the ocean is related to mechanisms by which energy is transferred to smaller scales, where mixing takes place. Using small-amplitude expansions, we investigate the mass transport generated by monochromatic internal wave beams between two lateral boundaries in the laminar regime. We find that the peculiar 3D structure of the lateral viscous boundary layers results in effective Reynolds stresses near the lateral walls, which generates a horizontal circulation in the interior. This induced circulation increase linearly over time, and as such, it may lead to the onset of wave-mean flow interactions and to turbulent mixing. Surprisingly, even very thin boundary layers (∼ 1% of wall to wall distance) have a significant impact on the mass transport in the interior. The theory is verified by laboratory experiments on particle transport induced by quasi-2D internal wave beams.