| Autor: |
Takahashi, Anne, Lien, Ren-Chieh, Kunze, Eric, Ma, Barry, Nakamura, Hirohiko, Nishina, Ayako, Tsutsumi, Eisuke, Inoue, Ryuichiro, Nagai, Takeyoshi, Endoh, Takahiro |
| Předmět: |
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| Zdroj: |
Journal of Physical Oceanography; Feb2024, Vol. 54 Issue 2, p461-484, 24p |
| Abstrakt: |
Generating mechanisms and parameterizations for enhanced turbulence in the wake of a seamount in the path of the Kuroshio are investigated. Full-depth profiles of finescale temperature, salinity, horizontal velocity, and microscale thermal-variance dissipation rate up- and downstream of the ∼10-km-wide seamount were measured with EM-APEX profiling floats and ADCP moorings. Energetic turbulent kinetic energy dissipation rates ε ∼ O ( 10 − 7 – 10 − 6 ) W kg − 1 and diapycnal diffusivities K ∼ O ( 10 − 2 ) m 2 s − 1 above the seamount flanks extend at least 20 km downstream. This extended turbulent wake length is inconsistent with isotropic turbulence, which is expected to decay in less than 100 m based on turbulence decay time of N−1 ∼ 100 s and the 0.5 m s−1 Kuroshio flow speed. Thus, the turbulent wake must be maintained by continuous replenishment which might arise from (i) nonlinear instability of a marginally unstable vortex wake, (ii) anisotropic stratified turbulence with expected downstream decay scales of 10–100 km, and/or (iii) lee-wave critical-layer trapping at the base of the Kuroshio. Three turbulence parameterizations operating on different scales, (i) finescale, (ii) large-eddy, and (iii) reduced-shear, are tested. Average ε vertical profiles are well reproduced by all three parameterizations. Vertical wavenumber spectra for shear and strain are saturated over 10–100 m vertical wavelengths comparable to water depth with spectral levels independent of ε and spectral slopes of −1, indicating that the wake flows are strongly nonlinear. In contrast, vertical divergence spectral levels increase with ε. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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