Simulating Interactions Between (Remote) Internal Waves and the Background Flows and Topography of the U.S. West Coast

This dissertation focuses on the simulation of remotely and locally generated semidiurnal internal tides (ITs) and near-inertial waves (NIWs), and how they interact with the California Current System (CCS) and the U.S. West Coast (USWC) topography. In Chapter II, we force Regional Ocean Modeling System (ROMS) simulations of the CCS with tides and remote internal waves (IWs) originating from as far as Hawaii, using a realistic global HYbrid Coordinate Ocean Model (HYCOM) simulation. To allow for optimal wave energy influx and minimize boundary reflections from the interior of the domain, we conduct boundary sensitivity tests on tide and IW forcing in multiple simulations with varying open boundary condition and sponge layer setups. Model validation with moorings and satellite data shows improved IW energy representation with remote IW forcing for the most optimal boundary configuration. In Chapter III, the fate of remotely generated semidiurnal ITs in the USWC continental margin is investigated using the best ROMS simulation from Chapter II. To separate the onshore and offshore propagating IT fluxes, we utilize a 2-dimensional Discrete Fourier Transform (DFT) technique. Integrated along the entire USWC margin, ~20% of the remote mode-1 onshore fluxes are reflected, 40% are scattered to modes 2-5, 7% are transmitted onto the continental shelf, and the remaining 33% are dissipated. However, these fractions vary along the USWC margin due to differences in stratification, slope criticality, topographic roughness, and angle of incidence. Lastly, the remote ITs enhance the advection and diffusion of heat and salt, reducing the thermocline stratification. In Chapter IV, we diagnose the full modal energy balance using a 2-km horizontal resolution nested simulation to study the interactions between IWs and the California Current System. The background flows supply energy to ITs and NIWs while scattering both, with NIW scattering being more pronounced than IT scattering. While topographic scattering of IW energy to small scales dominates in the shallow/rough region, wave-background flow interactions drive the resolved IW forward energy cascade in the deep/smooth ocean. Finally, by comparing two different months, we observe the background flow-induced IW scattering to depend on the strength of the background flows and stratification.