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Free Content Evidence of Vertical Coupling between the Kuroshio Extension and Topographically Controlled Deep Eddies

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Strong energy in the 30–60 day band was observed using 39 deep pressure and current records from the Kuroshio Extension System Study (KESS). Energy in this band accounted for 25–50% of the total deep-pressure variance and was strongest under the Kuroshio Extension jet axis. Often, deep-pressure anomalies propagated into the region from the north-northeast and locally intensified as they passed under and interacted with the Kuroshio Extension. The topographically controlled deep-pressure anomalies translate nearly along lines of constant f/H. Statistically significant coherence between 30–60 day upper- and deep-ocean streamfunction anomalies demonstrated that there was strong vertical coupling in that time band. Twenty-five percent of the total upper-ocean streamfunction variance was contained within the 30–60 day band near the Kuroshio Extension. Joint CEOFs of the upper- and deep-ocean streamfunctions revealed that near the axis of the Kuroshio Extension the phases were laterally offset alongstream, with the deep ocean leading the upper ocean. This arrangement is attributed to producing joint development of upper-ocean meanders and deep-pressure anomalies.

A numerical process model simulated the interaction of barotropic TRWs with an eastward-flowing baroclinic jet. When the TRWs, used as a surrogate for topographically steered deep-pressure anomalies, passed under the jet, they intensified and upper-ocean meanders steepened, much like the observed interactions. The model illustrates how the interaction between TRWs and an eastward-flowing jet, at its simplest level, can reproduce many of the major traits of our observations. The Ocean General Circulation Model for the Earth Simulator also showed similar processes in the 30–60 day band in the KESS region. The strongest variance in the deep fields occurred under the Kuroshio Extension. Upper and deep low- and high-pressure anomalies propagated south southwestward across the Kuroshio Extension, with model phase speeds and wavelengths matching the KESS observations.
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Document Type: Research Article

Publication date: September 1, 2012

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  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
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