Diagnosing and validating nonlinear internal wave processes in idealized, regional, and global ocean simulations

PI: Maarten Buijsmann, University of Southern Mississippi
Start Year: 2025 | Duration: 3  years
Partners: University of Michigan, University of Minnesota, Naval Research Laboratory

Project Abstract: 

This proposal aims to quantify the decay of primary-frequency internal tides into super-tidal internal waves due to wave-wave and wave-mean flow interactions using global, regional, and idealized model simulations, and validate those simulations with in-situ and satellite observations. Key observational data include full-depth moorings, CPIES, satellite altimetry (SWOT), and synthetic aperture radar (NISAR).  While previous studies have focused on Parametric Subharmonic Instabilities (PSI), this work emphasizes the “superharmonic cascade,” where primary-frequency internal tides interact to generate higher harmonic (supertidal) waves. This process, particularly pronounced in the tropics, leads to solitary wave-train formation that impact Navy operations and underwater acoustics. Internal tides also decay via wave-mean-flow interactions and scattering in eddy-rich regions. It is unclear how accurately any of these nonlinear processes are represented in the regional and global ocean models that provide operational forecasts for the US Navy. Here, we propose to quantify the impacts and accuracy of nonlinear processes in existing and newly proposed global and regional model simulations. To accomplish these goals, we propose to (1) conduct high-resolution measurements of nonlinear processes in internal-tide beams radiating from strong generation sites in tropical regions with and without strong mesoscale eddy activity and (2) perform high-resolution idealized, regional, and global simulations in synergy with these observations. The proposal comprises three collaborative efforts: 1. USM-led: High-resolution modeling of internal-tide decay mechanisms in idealized, regional, and global simulations. 2. SIO-led: In-situ data collection and analysis using moorings and CPIES in regions of strong nonlinear internal wave activity. 3. FSU-led: Evaluation and improvement of internal wave representation in the Navy’s data-assimilative forecast system using SWOT observations.  Together, these efforts will improve understanding, modeling accuracy, and forecasting of nonlinear internal wave processes in Navy operational models.