Internal‐Wave Dissipation Mechanisms and Vertical Structure in a High‐Resolution Regional Ocean Model.

Motivated by the importance of mixing arising from dissipating internal waves (IWs), vertical profiles of internal‐wave dissipation from a high‐resolution regional ocean model are compared with finestructure estimates made from observations. A horizontal viscosity scheme restricted to only act on horizontally rotational modes (such as eddies) is introduced and tested. At lower resolutions with horizontal grid spacings of 2 km, the modeled IW dissipation from numerical model agrees reasonably well with observations in some cases when the restricted form of horizontal viscosity is used. This suggests the possibility that if restricted forms of horizontal viscosity are adopted by global models with similar resolutions, they could be used to diagnose and map IW dissipation distributions. At higher resolutions with horizontal grid spacings of ∼250 m, the dissipation from vertical shear and horizontal viscosity act much more strongly resulting in dissipation overestimates; however, the vertical‐shear dissipation itself is found to agree well with observations. Plain Language Summary: Oceanic mixing impacts circulation, stratification (layering by density), and the uptake and transport of heat and nutrients. Over most of the ocean, mixing is caused by the breaking (turnover) of internal waves lying on the interfaces of density layers. Most ocean models do not contain a resolved internal wavefield, and therefore must parameterize internal wave (IW) mixing based upon external information. Recently developed high‐resolution ocean models with credible representations of internal waves may make it possible to map and understand global IW mixing without use of external information. Here we compare vertical profiles (profiles in depth) of IW dissipation in a regional model, which can be used to understand sensitivities to numerical schemes and grid spacings. With grid spacings that are attainable in global models, modeled dissipation profiles lie somewhat close to observed profiles, as long as certain choices are made within the numerical schemes. One numerical dissipation scheme is designed to realistically remove energy from eddy fields, which are the non‐wavelike motions in the ocean, and we have adapted this scheme to act less strongly on internal waves. Using this modified scheme, we find that high‐resolution global models may already be able to map IW dissipation. Key Points: Vertical profiles of internal wave (IW) dissipation in high‐resolution regional ocean simulations are compared with observed profilesProfiles in runs with a restricted form of horizontal viscosity and resolutions attainable in global models are close to observationsResults suggest high‐resolution global models can be used to map IW dissipation after numerical sensitivities are tested in regional models [ABSTRACT FROM AUTHOR]