Topographically generated internal waves in the open ocean

Abstract

The generation of internal waves by the interaction of deep ocean flows with bottom topography is considered. The interaction of quasi-steady currents with the bottom topography is found to produce an internal wave drag and associated momentum flux of roughly ½ dyn/cm2, which is comparable to the average wind stress on the ocean surface. The waves are probably dissipated by critical layer phenomena in the lowest kilometer or so of the ocean, the result being a wave-induced vertical mixing coefficient of order 10 cm2/s in that portion of the water column. The interaction of the barotropic tide with the bottom topography is found to result in a flux of energy of order 1 erg/cm2 s into the internal tide, which may represent a nonnegligible sink of the tidal energy. This mechanism appears to be capable of supplying a significant portion of the observed internal wave energy in the ocean. The internal tide is probably dissipated by inherently nonlinear phenomena: spectral transport by weak interactions and, in the upper oceans, strong interactions manifested by localized instabilities resulting in isolated patches of turbulence.