Collaborative Research: Causes and Effects of Shelf-Edge Internal Tide Variability

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Internal tide generation and propagation near continental slopes will be studied using a four-dimensional numerical simulation and diagnosis approach. The purpose is to explain observed variability in internal tides and the nonlinear waves they spawn. The study will concentrate on long wavelength linear internal waves (internal tides) generated from sub-critical tidal flow (current speed less than wave speed), ubiquitous around the world. Three internal tide effects will be examined: variable generation, heterogeneous propagation, and conversion to nonlinear waveform. A set of simulations will be performed with the MIT Multidisciplinary Simulation, Estimation, and Assimilation System (MSEAS), mostly with the hydrostatic primitive equation model already tuned at mesoscales via comparison with data. Modeled configurations will range from idealized bathymetric, stratification, and flow conditions to realistic conditions obtained via data-driven modeling. Inter-comparisons of the collected results will divulge the physics of variable four-dimensional internal tide generation and propagation, with the intent of describing how the process occurs in the real ocean. The new MSEAS non-hydrostatic model will then be used to study nonlinear conversion processes. Applicability of the results to the real ocean will be verified via comparison to remote sensing and in situ data from a one-month long experiment.This work will lead to better understanding and accurate modeling of interactions of mesoscale and sub-mesoscale features, surface and internal tides, origins of nonlinear internal waves, and strong variability of these processes. Hydrostatic and non-hydrostatic primitive equation models using different numerical schemes will be evaluated for internal tide predictions. Internal tides and nonlinear internal waves, and their interactions with larger scales, impact a wide range of natural and man-made activities. These include life cycles and distributions of oxygen, nutrients, plankton, fish, and other predators, naval operations and surveillance, underwater acoustics, and patterns of diapycnal mixing and water mass development in the summer season of strong stratification. In addition, these waves are a major source of shear, strong bottom currents, and cycling of water between sunlight and darkness. They are energy sources for mixing processes which are important to benthic habitat, plankton and fish life cycles, and distributions of nutrients and contaminants. All results, including model outputs, will be disseminated to ocean researchers and communities. A coastal oceanography student will be educated and a post-doctoral fellow further instructed.