UC San Diego

This dissertation explores submesoscale dynamics in salinity-stratified oceans, strongly influenced by freshwater input through rivers and storms. The submesoscale describes a regime of dynamics that occur at lateral scales of O(1-10 km), where the planetary vorticity is in balance with the relative vorticity of the flow, and are typically associated with fronts and filaments. At these scales, vertical velocities, facilitated by various instabilities, become large leading to the vertical exchange of heat, salt, and nutrients within the ocean boundary layer. The first chapter observes patchy rain on an ocean that varies in stratification using high-resolution in-situ observations and satellite data in the Bay of Bengal. Inspired by the spatial variability of the rain and surface ocean, we investigate the relative impacts of 1-D processes on frontogenesis using a general ocean turbulence model. The results of this chapter suggest that rain can be conditionally frontogenetic with implications for small-scale instabilities. The second chapter captures these small-scale instabilities in action through high-resolution in-situ observations of the subduction of a cold and salty filament in the Bay of Bengal. Through a stability analysis, we discover the importance of small-scale lateral temperature variability, creating inversions within barrier layers facilitated through symmetric and inertial instabilities and secondary circulations. The third chapter focuses on the temporal evolution of the mesoscale in the Gulf of Mexico, which cascades to the submesoscale, and shifting dynamics in the Loop Current region. A novel analysis of satellite-derived products reveals changes in Loop Current eddy behavior and justification for an increasingly energetic basin. The results suggest that recent years have witnessed prolonged Loop Current retracted phases due to large cyclonic eddies while increases in the kinetic energy of the basin may be attributed to increases in sea level anomalies. In the Bay of Bengal, the findings of this dissertation can improve our understanding of air-sea interactions and support the parameterization of models for monsoon forecasting. In the Gulf of Mexico, the results highlight possible shifts in circulation patterns, important to the transport of biological, chemical, and thermal properties throughout the basin.