Laboratory and numerical studies of internal wave generation and propagation in the ocean

Internal waves are generated in the ocean by oscillating tidal flow over bottom topography such as ridges, seamounts, and continental slopes. They are similar to the more familiar surface waves, but not being constrained to move on the surface, propagate throughout the bulk of the world oceans. Internal waves transmit energy over thousands of kilometers, ultimately breaking and releasing their energy into turbulence and mixing. Where these internal waves are generated, as well as where and how they break and cause mixing, has important effects on the general circulation of the ocean, which is in turn a major component in earth's climate. As a first step in a more thorough understanding of the evolution of internal waves in the ocean, it is important to characterize their generation. The two-dimensional generation problem has been studied for four decades, with ample experimental, numerical, and theoretical results. Most of this past work has also been done using linear, inviscid approximations. However, wave generation in the ocean is three-dimensional (3D), and in many locations, nonlinear and viscous effects can be significant. Recent advances in experimental and numerical techniques are only now making the fully nonlinear, 3D generation process accessible. We utilize these new techniques to perform both laboratory experiments and numerical simulations on internal wave generation in 3D. We find that a significant component of the internal wave field generated by tidal flow over 3D topography is radiated in the direction perpendicular to the tidal forcing direction. This could lead to substantial improvements of global internal wave generation models. In addition, we have developed a new method for statistical analysis of ocean data sets, and have found large regions in the deep ocean where internal waves may not propagate. This will also have important effects on the way researchers study the propagation of internal waves, which, when propagating downward, were previously thought to always reflect from the sea floor.