Publication Date:
2022-05-25
Description:
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009.
Description:
This thesis examines the nature of eddy-mean flow interactions in western boundary
current jets and recirculation gyre dynamics from both theoretical and observational
perspectives. It includes theoretical studies of eddy-mean flow interactions in idealized
configurations relevant to western boundary current jet systems, namely (i) a study
of the mechanism by which eddies generated from a localized forcing drive mean
recirculation gyres through the process of nonlinear rectification; and (ii) a study of
the role of eddies in the downstream evolution of a baroclinic jet subject to mixed
instabilities. It also includes an observational analysis to characterize eddy-mean flow
interactions in the Kuroshio Extension using data from the downstream location of
maximum eddy kinetic energy in the jet.
New insights are presented into a rectification mechanism by which eddies drive the
recirculation gyres observed in western boundary current systems. Via this mechanism,
eddies drive the recirculations by an up-gradient eddy potential vorticity flux
inside a localized region of eddy activity. The effectiveness of the process depends
on the properties of the energy radiation from the region, which in turn depends
on the population of waves excited. In the zonally-evolving western boundary current
jet, eddies also act to stabilize the unstable jet through down-gradient potential
vorticity fluxes. In this configuration, the role of eddies depends critically on their
downstream location relative to where the unstable time-mean jet first becomes stabilized
by the eddy activity. The zonal advection of eddy activity from upstream
of this location is fundamental to the mechanism permitting the eddies to drive the
mean flows. Observational results are presented that provide the first clear evidence
of a northern recirculation gyre in the Kuroshio Extension, as well as support for the
hypothesis that the recirculations are, at least partially, eddy-driven. Support for
the idealized studies’ relevance to the oceanic regime is provided both by indications
that various model simplifications are appropriate to the observed system, as well as
by demonstrated consistencies between model predictions and observational results
in the downstream development of time-mean and eddy properties.
Description:
Funding was for this research and my education was provided by the MIT Presidential
Fellowship and NSF grants OCE-0220161 and OCE-0825550. The financial
assistance of the Houghton Fund, the MIT Student Assistance Fund, and WHOI
Academic Programs is also gratefully acknowledged.
Keywords:
Ocean currents
;
Oceanography
Repository Name:
Woods Hole Open Access Server
Type:
Thesis
Format:
application/pdf