Expermental Measurements of Internal Waves

Internal waves are propagating disturbances of gravitationally-stable density stratifications. They are ubiquitous in the Earth’s oceans, being generated by flow over ocean-floor topography and sea-surface winds. Dissipation of these internal waves impacts the Earth’s climate by shaping the continental slopes, affecting plankton distribution, and influencing large-scale ocean circulation. From an engineering perspective, internal waves affect the performance of underwater technology, such as acoustic communication, submersible vehicles and marine cabling. A detailed understanding of all aspects of internal wave generation and evolution is therefore both profoundly and practically important.

We are using advanced laboratory experimental techniques to research problems that are not amenable to analysis and numerical simulation, and are hampered by the inevitable lack of detailed field data. Our research is centered on a state-of-the-art 5.5-meter wave tank, with a computer-controlled system to establish nonlinear stratifications and sophisticated motion control apparatus. Advanced measurement tools include Synthetic Schlieren and high-resolution PIV/PTV systems. We are presently focused on addressing outstanding issues of internal wave generation by topography, a topic that came to the fore ten years ago. While there have recently been significant theoretical advances, there is a complete absence of experimental data on this problem.

To ensure the relevance of our laboratory work to oceanic problems, group members participate in ocean-going research. We were recently involved in the NSF funded IWAP study, investigating instabilities of internal waves near the critical latitude. The research cruise used a combination of moorings and ship-based sonar to detect high levels of inertial shear generated by the instabilities. The picture to the left shows Professor Peacock recovering one of the cruise moorings. Future research will focus on the outstanding issues of internal tide generation by 3D topography and the dissipation of the internal tide.