UC San Diego

The surface layer of the ocean is a critical component of the ocean-atmosphere system. The momentum and heat transfer that occur here, as well as tidal forcing, result in energetic currents across a wide range of length and time scales. Because the surface is observable from land and space, it is the subject of extensive study from land-based and satellite observation systems. Only recently, however, have spatial resolutions from satellite instruments approached the submesoscale, which evolves at time scales comparable to or faster than repeat orbit sampling rates. At the same time, land-based radar networks have matured such that more than a decade of surface current observations at kilometer scale resolution are available from many regions around the world, unconstrained by the timing of orbits that affect satellites but are limited to coastlines. This leads to the central motivating question that this dissertation seeks to address: what can coastal radar data reveal about short time scale processes that could be useful to the goals of recent and upcoming Earth observation satellite missions? This work is limited to examining the surface expression of internal tides and diurnal wind-driven currents, as both are energetic processes at known frequencies, lending themselves well to harmonic analysis.

In Chapter 1, a novel tidal harmonic analysis method is presented, following from previous tidal analysis and incorporating Bayesian principles and prior statistics to inform the least squares fitting procedure. This method is applied in Chapter 2 to high-frequency radar data from the California Current System in order to characterize tidal currents in that region, finding a phase structure indicative of internal tidal propagation and a complicated spatial distribution of the fraction of tidal energy deemed to result from modulation by other processes in the ocean. Finally, Chapter 3 uses the same method on currents and winds in order to characterize the diurnal wind-driven current, finding the times of day that these quantities peak, their level of coherence, and the angle between them as a function of frequency. These chapters provide a detailed view of these processes in a well-studied coastal region, with implications for satellite oceanography.