Studies of internal tide generation at a slope with nonlinear and linearized simulations: Dynamics and implications for ocean acoustics

Abstract

Under the framework of a project to model submesoscale processes in support of underwater acoustic predictions, flow fields within an across-shelf section of continental shelf and slope have been modeled with the Regional Ocean Modeling System (ROMS). The model has been run with several versions of ocean dynamics in order to deduce the effects of various dynamical processes. The findings are that momentum advection causes nonlinear effects to occur in the formation of internal tides (internal waves) from barotropic surface tides, not unexpectedly. The nonlinear nature of the process is quantified. This study differs from many prior computational studies of internal tide generation at sloping bathymetry by having a very high resolution, by having very low background eddy viscosity and diffusivity, and by admitting the majority of mixing through a turbulent mixing closure scheme. The initial new results shown here appear in the nonlinear simulations. Zones of nonlinear wave-wave interactions are mapped with bispectrum and bicoherence analysis. The net result of the nonlinearity and weak background eddy mixing is a broadband internal wave spectrum. Technical aspects of using information from internal tide generation models such as this to initialize coastal internal wave models for use with acoustic propagation models are discussed.

Integrated Modeling and Analysis of Physical Oceanographic and Acoustic Processes

“…Here, barotropic tidal flows force internal tides at the continental shelf edge, with the slope where the internal waves are generated being steep with respect to internal wave characteristics (supercritical slope) and the barotropic currents being slow with respect to internal wave speed (subcritical Froude number). The work is described in a conference paper (Duda, Zhang and Lin, 2012), and a recently accepted journal article . The modeling is fully nonlinear, using the Boussinesq-approximation based primitive equations, although the pressure is approximated as hydrostatic (NHP physics not allowed).…”