Linking topographic internal wave radiation to near-field processes, dissipation and mixing

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Intellectual Merit: The project addresses the dynamics of tidal flows over isolated topographic features, focusing in particular on the regime in parameter space where nonlinearity leads to significant local mixing and dissipation in comparison to the rate of wave radiation in the overall energy balance. This flow regime occurs both in the deep ocean and also near tall isolated features such as the Hawaiian Ridge. The relative importance of near-field dissipation and mixing on the one hand, and radiation to the far-field on the other, varies between sites and depends on factors that are not presently well understood. The primary objective is to understand the dynamics linking nonlinear local flow phenomena to the intensity and character of wave radiation to the far field and to relate the rates of mixing, dissipation and radiation at various frequencies to parameters characterizing the flow and the topography. The project will utilize an experimental approach using high-resolution, three-dimensional numerical simulations run on parallel supercomputers. The simulations will resolve phenomena such as boundary layer separation and shear instabilities and about a decade of the inertial sub-range. The numerical model was designed specifically for process-oriented studies such as these and combines high-accuracy numerical methods with efficient implementation on distributed memory computing facilities. Broader Impacts: Stratified flow over topography is a fundamental aspect of oceanic motion characterized by a wide range of phenomenology. The processes that produce internal waves that radiate to the far field can coexist and be dynamically coupled to near-field phenomena such as high-drag states, internal hydraulic jumps, dissipation and mixing. Understanding the physics linking these local and global responses is an important precursor to the successful parameterization of energy conversion and therefore internal wave driven mixing. The project will directly support the education and training of one Ph.D. student in Physical Oceanography. Aspects of this work will be incorporated into graduate classes taught by the investigators in Environmental Fluid Dynamics and Turbulence in Environmental Flows to students in Physical Oceanography, Climate Sciences and Mechanical and Aerospace Engineering. The investigators will also maintain a project web page disseminating numerical tools with the objective of making all of the numerical results: reproducible by other groups; useful as a starting point for related or extended studies; and suitable as educational examples of computational fluid mechanics. Results will also be integrated into public lectures given through the San Diego Flight Standards District Office on wave flights and the hazards of down slope flows.