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Causes and Effects of Shelf-edge Internal Tide Variability (NSF-Shelf-IT)

Internal tide generation and propagation near continental slopes are being 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 concentrates on long wavelength linear internal waves (internal tides) generated from subcritical tidal flow (current speed less than wave speed), ubiquitous around the world. Three internal tide effects are being examined: variable generation, heterogeneous propagation (i.e. focusing), and conversion to nonlinear waveform. The first two effects, largely unexplored thus far, will create wave energy density structure, and may give spatial/temporal structure to the nonlinear conversion process. A set of simulations are being performed with 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. The main application region is the Middle-Atlantic Bight because large constraining data sets and available tuned model, but Asian Seas areas, also with existing models and data sets, will be briefly explored to examine inter-regional differences.