The Internal Wave Spectrum and Boundary Mixing in the Sub-Tropical South Atlantic

PI: Polzin, Kurt (Woods Hole Oceanographic Institution)
Start Year: 2022 | Duration: 3 years
Partners: University of Delaware, University of Maryland, Georgia Institute of Technology, and National Research Laboratory

Project Abstract:

This proposal represents an intersection between the expanding capability of global scale Ocean Circulation Models (OCMs) to represent internal gravity waves, their dynamics and mixing with characterizing the oceanic internal wavefield at regional scales through a targeted field campaign and numerical investigations. Such characterization will be obtained using observationally based metrics of ocean mixing and theoretical treatments of nonlinear wave-wave interactions. The wavefield will be linked to the structure of the ocean’s bottom boundary layer and their coupling resolved. A moored array will be deployed in the Brazil Basin to quantify near boundary flow distortions due to finite amplitude topography, near boundary internal wave breaking, and momentum and buoyancy fluxes in both turbulent and internal wavebands (i.e. drag and mixing). Extant data obtained as part of a Tracer Release Experiment in the same domain and data from the Global Drifter Program will be used to create a regional statistical characterization of the oceanic internal wavefield in the Sub-Tropical South Atlantic. This characterization will be compared to a hierarchy of five models: an operational forecast model (HYCOM), O(1-3) km horizontal resolution ROMS-CROCO, nonhydrostatic ROMS-CROCO ’mountain scale’ simulations with 50 m resolution and 1:1 grid aspect ratio, realistic Large Eddy Simulations (LES), and a quasi-analytic spectral representation of the internal wave energy spectrum. The proposed work I synergistic: the field characterization represents ground truth, the quasi-analytic model is constrained by those highly resolved data and can be modified to critique how a numerical model’s truncation of topographic variability impacts the mid-water column internal wavefield, the global models assist assessment of non-local generation and propagation not represented in the quasi-analytic model, quantification of nonlinear wave-wave interactions in the ’mountain scale’ simulations provides insight into theoretical treatments. Observed data and LES permit investigation of interactions between boundary layer dynamics, wave generation and the forward cascade to turbulence.