Revisiting internal wave generation by tide‐topography interaction

Abstract

To clarify the physics responsible for tidal generation of internal waves over abyssal small‐scale bottom topography, we carry out a series of numerical experiments using a vertically two‐dimensional primitive equation model. It is found that the stratified fluid response can be categorized into four dynamical regimes in terms of two dimensionless parameters related to tidal advection effects and buoyancy effects. Under parameters corresponding to the real abyssal ocean, quasi‐steady internal waves are created over the bottom topography only during the limited time interval centered at the maximum of opposing tidal flow; since the created internal waves cannot maintain the quasi‐steady balance with the decreasing tidal flow, they then start propagating upstream. This “partial quasi‐steady response” in the abyssal ocean is found to be quite similar to the response actually observed in the shallow ocean, causing the widespread misinterpretation that strong tide‐topography interactions in the shallow ocean can generate quasi‐steady lee waves. In the present study, we clearly distinguish between the dynamical regimes corresponding to “quasi‐steady response” and partial quasi‐steady response to dispel this confusion about the interpretation of tide‐topography interactions, not only for the abyssal ocean but also for the shallow ocean.