SUBMESOSCALE VORTICES AND NEAR-INERTIAL WAVES IN COASTAL BUOYANCY-DRIVEN FLOW

As two ubiquitous features in open oceans, baroclinic instability vortices and near-inertial waves can coexist in coastal zones under certain conditions and exhibit unique features. This study attempts to improve the fundamental understanding of the submesoscale baroclinic instabilities and near-inertial waves in coastal buoyancy-driven flows. Baroclinic instabilities in coastal buoyancy-driven flows exhibit the self-inhibiting feature (the reduction of the growth rate), which is not revealed in the classical quasi-geostrophic theory. The first part of this study explores the non-geostrophic baroclinic instability theory adapted to the scenario with sloping bathymetry and demonstrates that the suppression of instabilities is related to the Rossby wave resonance. A nondimensional parameter, slope-relative Burger number, is defined for the instability suppression. On the other hand, near-inertial waves in coastal buoyancy-driven flows can be modified by the curved fronts of the instability vortices, which is not revealed in the previous modification theories accounting for straight, jet-like fronts. The second part of this study focuses on the curvature effect of a front on modifying the properties of near-inertial waves. The primary finding is that the waves modified by a baroclinic vortex can be trapped deeper and hence cause deeper mixing than the ones modified by a front without curvature. Furthermore, to better simulate coastal buoyancy-driven flows, the simulation errors caused by temporally subsampling winds are quantified in the last part of this study. The primary finding is that the simulation error is proportional (1:1) to the fraction of the energy missing in the high-frequency wind caused by subsampling. Analyzing the fast Fourier transformation spectrum of a single-point wind measurement in the simulation region is helpful for estimating simulation errors due to temporal resolution