This study was motivated by the Kuroshio Extension System Study (KESS), which provides an unprecedented suite of observations uniquely suited to study the jet, its eddy variability, and their interactions. The goals of the study are to characterize eddy-mean flow interactions in the Kuroshio Extension (KE) from the KESS and supporting observations, to examine eddy-mean flow interactions in idealized configurations relevant to WBC jet extension systems, and finally to test the relevance of the theoretical understanding derived from these idealized studies to the oceanic system. This work WILL result in new insights into a mechanism by which eddies from a localized forcing can drive recirculation gyres of a strength consistent with the deep recirculation velocities observed in the KE and Gulf Stream, as well as support for the hypothesis that the recirculation associated with these jet systems are, at least partially, eddy-driven. In addition, new insights will be gained into what may determine the properties of the mean jet and its recirculation as they evolve downstream as a consequence of the nonlinear dynamics.
Eddy energies are orders of magnitude larger along the mean paths of WBC jets compared to most other regions of the ocean and we expect eddy variability to play an important role in the dynamics of these systems. The KESS data set provides a unique opportunity to extend our present understanding of the nature and importance of this role, in particular, allowing us to understand how theories about eddy-mean flow interaction in unstable jets apply to the actual ocean. One anticipated result of this research is improved understanding of the processes that govern the strength and structure of the recirculation gyres that flank WBC jets. Recirculation gyres fundamentally alter the dynamical structure of the jet and add significantly to the net transport of these currents. They also are important as the sites of subtropical mode water formation. This work will test the hypothesis that these recirculation zones are eddy-driven and seek to determine the relative importance of barotropic and baroclinic instability in this process.
Results from this work promise an improved understanding of WBC jets, as eddy-mean flow interactions in these systems are likely critical to their overall dynamics. WBCs are one of the foremost components in global heat transport and thus in regulating the global climate. As such, the lessons learned here will have important application to the evaluation of realistic ocean general circulation models required for climate studies, and also to the design of an efficient and effective monitoring strategy in the KE region for eventual achievement of CLIVAR goals. This work likely has implications for ocean modeling. It may lead to an improved understanding of the impact and importance of having various eddy processes resolved in these systems. The insights into the dynamical mechanisms that are sought may suggest suitable parameterizations for the effects of unresolved eddies.
