Talk Abstract:
Oceanic lee waves are generated when quasi-steady flows interact with rough topography at the bottom of the ocean. These internal waves provide an important sink of energy and momentum from the mean flow, especially in the Southern Ocean where they are a leading order mechanism for diapycnal mixing. Linear theory with a spectral representation of abyssal hill topography is generally used to estimate lee wave generation for use in parameterisations, and has been verified against idealised simulations. Here, we use a realistic wave resolving simulation of the Drake Passage to investigate the utility of such parameterisations for areas of complex large scale topography. The flow is often blocked and split by large amplitude topographic features, calling into question the spectral representation of small scale topography for lee wave generation. We show that the nature of lee waves in such regions can be misrepresented by a spectral approach to topographic representation, leading to an overestimate of wave energy flux and an underestimate of wave nonlinearity.