Turbulent mixing within the Kuroshio in the Tokara Strait

Eisuke Tsutsumi, Takeshi Matsuno, Ren Chieh Lien, Hirohiko Nakamura, Tomoharu Senjyu, Xinyu Guo

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

Turbulent mixing and background current were observed using a microstructure profiler and acoustic Doppler current profilers in the Tokara Strait, where many seamounts and small islands exist within the route of the Kuroshio in the East China Sea. Vertical structure and water properties of the Kuroshio were greatly modified downstream from shallow seamounts. In the lee of a seamount crest at 200 m depth, the modification made the flow tend to shear instability, and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site, to Kρ ∼ O(10−3)–O(10−2) m2 s−1. A one-dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature-salinity profile. However, the estimated diffusion time-scale is at least 10 times longer than the observed advection time-scale. This suggests that the eddy diffusivity reaches to O(10−1) m2 s−1 in the vicinity of the seamount. At a site away from the abrupt topography, eddy diffusivity was also elevated to O(10−3) m2 s−1, and was associated with shear instability presumably induced by the Kuroshio shear and near-inertial internal-wave shear. Our study suggests that a better prediction of current, water-mass properties, and nutrients within the Kuroshio requires accurate understanding and parameterization of flow-topography interaction such as internal hydraulics, the associated internal-wave processes, and turbulent mixing processes.

Original languageEnglish
Pages (from-to)7082-7094
Number of pages13
JournalJournal of Geophysical Research: Oceans
Volume122
Issue number9
DOIs
Publication statusPublished - Sep 2017
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Oceanography

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