UC San Diego

The breaking of oceanic internal waves is an essential part of the deep-ocean mixing processes that contribute to the general circulation of the ocean, the exchange of heat and gases with the atmosphere, the distribution of nutrients and the dispersal of pollutants. It is essential to improve our understanding of how these waves evolve toward dissipation. In this thesis ray theory, numerical simulations, and observations are used to examine the refraction of short internal-wave packets by time- dependent background shear profiles to test the validity and explore the limitations of currently used models of short internal waves propagating through steady shear in the deep ocean. Types of possible interactions due to initial short wave parameters are categorized. An analysis of observational ocean data supports the simulation results which show a change in the propagation of short internal waves and their properties when time-dependence in the background shear profile is taken into account. Through ray theory and simulations, a net exchange of energy to the background wave is found, which is consistent with ocean data. It is found through ray theory that the highest frequency short waves are the most likely to break, and these calculated locations are also consistent with ocean observations. The results of our simulations and analysis are enough to show that the ignored physical effect of the time-dependence in the long -wave shear can make a significant difference to short- wave behavior and should be taken into account in the models