Eddy-Mean Flow Interactions in Western Boundary Current Jets

摘要

This thesis examines eddy-mean flow interactions in western boundary current jets via theoretical studies of eddy-mean flow interactions in idealized configurations and an observational analysis to characterize eddy- mean flow interactions in the Kuroshio Extension. Theoretical studies are made of the mechanism by which eddies drive recirculation gyres through nonlinear rectification, and the role that eddies play in the downstream evolution of a baroclinic jet subject to mixed instabilities. The observational study seeks to evaluate the relevance of these idealized studies to the actual oceanic system. Results include a new understanding that the eddy-driven rectified mean flow results from an up gradient eddy potential vorticity flux, and that the strength of the eddy-driven circulation depends on the energy radiation away from the forcing, which in turn depends on the population of waves excited. The relevance of this mechanism to the eddy-driving of recirculation gyres in an idealized jet model is demonstrated. Finally, the first clear observational evidence of a northern recirculation gyre in the Kuroshio Extension is presented, as is observational support for the hypothesis that the recirculations are, at least partially, eddy-driven, consistent with the mechanism described.