Mass transport and shear-flow dispersion due to nonlinear internal gravity waves [electronic resource]

Internal gravity waves are a ubiquitous physical phenomenon throughout the world's oceans. In the coastal ocean, internal wave-induced drift has been shown to be an important mechanism for mass transport with implications for the advection and dispersion of biology, contaminants, sediment and other particulate matter as well as the integrity of marine structures. We conduct numerical simulations of internal waves and particle clouds to learn more about the fundamentals of the wave-induced mass transport. We consider linear periodic and nonlinear internal solitary waves (of depression), including internal solitary wave trains that emerge from the internal tide. Nonlinear internal solitary waves are generated by solving the nonlinear Drubeil-Jacotin-Long (DJL) equation and the particle drift is computed with a Lagrangian particle tracking code. By introducing a vertical diffusivity with a random walk, we compute the shear-flow dispersion for DJL waves with and without trapped cores for several types of stratification and wave amplitudes. Our results show that internal waves have the potential to transport mass over large distances in a matter of hours. The vertical profile of the wave-induced transport varies with depth and is fundamentally different for linear periodic waves and internal solitary waves. In the former case, the drift is positive above and below the pycnocline and negative at the pycnoline. In the latter case, the drift is positive in the upper layer, zero at the pycnocline and negative in the lower layer. The maximum drift is found at the ocean surface and is up to one order of magnitude larger for solitary waves than for periodic waves with the same energy. For the longitudinal shear-flow dispersion due to internal solitary waves, depending on the Peclet number, there are three separate regimes. In the first regime, the longitudinal dispersion is inversely proportional to the vertical diffusivity, which is similar to Taylor's pipe flow. In the second regime, the dispersion remains constant with the Peclet number, while in the third regime the longitudinal dispersion is proportional to the vertical diffusivity, which is consistent with Saffman's shear-flow dispersion in unbounded fluids. Finally, we study the particle entrainment and detrainment due to large nonlinear internal solitary waves with trapped cores as a function of the Peclet number. We find that the maximum fraction of particles that is entrained into the core is inversely proportional to the Peclet number and ranges from values as low as 1% for large Peclet numbers to 16% for small Peclet numbers. Dispersion estimates based on the Peclet number related to observations of internal solitary waves in different regions, including the South China Sea, Oregon Continental Shelf and Monterey Bay, indicate that internal solitary waves can generate shear-flow dispersion that is of the same order as other processes in the ocean that are typically thought to be much stronger at driving shear-flow dispersion than internal waves.

Advisor: Fringer Oliver B. (Oliver Bartlett) primary advisor. Thesis advisor
Koseff Jeffrey Russell advisor. Thesis advisor
Monismith Stephen Gene advisor. Thesis advisor