Date of Award
2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Oceanography
Department
Oceanography
First Advisor
Kathleen Donohue
Abstract
Eddies are an integral component of the large-scale ocean circulation and climate system. They play a significant role in redistributing heat and energy around the globe, locally enhance primary productivity and aid in carbon sequestration. They primarily result from instability processes that modify large scale flow into smaller scale features, often facilitated by interactions with large topography. This dissertation is focused on these interactions, the dynamics that govern the generation and maintenance of mesoscale eddies and global implications for our climate system.
The role of topography in the Gulf of Mexico Loop Current Eddy (LCE) separation cycle is investigated in Chapter 1. Observations from an array of 24 current and pressure recording inverted echo sounders (CPIES) is used to document the generation and radiation of deep energy during (LCE) separation events. High-frequency variability, characteristic of topographic Rossby waves (TRWs) is found to dominate the array's northwest corner, in the vicinity of the Mississippi Fan. Their generation, which coincides with each LCE separation, is attributed to an upper-lower layer resonant coupling between surface meanders and the sloping topography of the Mississippi Fan.
Cross-frontal exchange facilitated by mesoscale eddies in the lee of major topographic features of the Southern Ocean is fundamental to the global overturning circulation. In Chapter 2, 12 years of Argo data is used to observe patterns of cross-frontal exchange in the Southeast Indian Ridge (SEIR) system, a relatively under-observed region known to be a hot spot of exchange. Spice variance, a proxy for cross-frontal exchange, is elevated downstream from the ridge in nearly every streamline. Employing a mixing length framework, we observe a highly localized pattern of diffusivity, peaking between the crest and trough of the standing meander in the lee of the ridge. Spatial patterns of eddy diffusivity correlate to an along stream increase in eddy kinetic energy. In chapter 3, the physical mechanisms governing the generation and maintenance of the SEIR eddy field are investigated using a wave activity flux framework and 3 years of high resolution numerical model output. Background dynamics are found to be primarily governed by baroclinic conversion from the mean to eddy field while events, that largely coincide with patterns of eddy kinetic energy, are dominated by barotropic conversion. The event driven variability is shown to be analogous to atmospheric downstream development, a process by which wave-train like propagation is sustained by the barotropic growth, flux and decay of energy in the along stream direction.
Recommended Citation
Exley, Alexis Johnson, "EDDY-TOPOGRAPHIC INTERACTIONS" (2024). Open Access Dissertations. Paper 1693.
https://digitalcommons.uri.edu/oa_diss/1693