Ph.D. Defense Seminar of Zachary Taebel

Laboratory studies of Energy Cascades in Surface and Internal Wave Turbulence

Nonlinear interactions within a system of random linear waves cascade energy and other conserved quantities from injection to dissipation scales. This process, termed wave turbulence, is useful for explaining the evolution of the wind-driven ocean surface, and the maintenance of the internal wave continuum. The latter situation is particularly relevant, as wave breaking drives interior mixing, necessary to close the global overturning circulation. Despite the analytical and numerical success of wave turbulence, corroborating its theoretical predictions in real-world environments, such as laboratory facilities, remains challenging. Here I present results from novel experimental studies of both surface and internal wave turbulence. For surface waves, I show that even in an idealized system that rigorously imposes the assumptions of theory, the system is not in complete agreement with wave turbulence. Through a spatiotemporal analysis, and the usage of higher order statistics, I connect this discrepancy to secondary effects such as dissipation and intermittency. For internal waves, I show that at sufficiently high Reynolds number, wave turbulence can transfer energy from tidal injection scales to overturning scales, which subsequently fuels Kolmogorov turbulence and mixing. Within this cascade, parametric subharmonic instability plays an important role in degrading the internal tide.