Second-mode internal tides in the East China Sea deduced from historical hydrocasts and a model

We present four sets of concurrent ADCP data obtained from the East China Sea shelf, and it suggests that near-inertial waves induced by parametric subharmonic instability (PSI) associated with harmonic transfer beyond diurnal critical latitude (O1:27.6&#176;, K1:30&#176;). Two type different nonlinear behavior (harmonic transfer and subharmonic transfer) occur varying with the latitude on different location. The velocity data indicated a transfer of diurnal internal tidal energy poleward of the diurnal critical latitude. Kinetic energy and shear spectra analysis at these moorings reveals that the prominent peaks enhance and appear at not only at the even order of diurnal tide such as semidiurnal band, 4cpd, 6cpd and even 8cpd, but also some unfamiliar odd harmonics 3cpd and 5cpd. Furthermore, additional energy is converted to higher mode locally through continuum internal wave spectrum. Besides the harmonic transfer, on the critical latitude for D2/2 wave(28.9&#176;), D1 wave is extracted from a D2 tidal driven model output current. PSI conversion of semidiurnal internal tidal energy was confirmed by spectra analysis and bi-spectra, because of the distinguish of M2/2 separated from the diurnal tidal (O1, K1).

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Parametric Subharmonic Instability of the Semidiurnal Internal Tides at the East China Sea Shelf Slope

Journal of Physical Oceanography ◽

10.1175/jpo-d-19-0163.1 ◽

2020 ◽

Vol 50 (4) ◽

pp. 907-920

Author(s):

Wei Yang ◽

Hao Wei ◽

Liang Zhao

Keyword(s):

East China Sea ◽

Relative Vorticity ◽

Internal Tides ◽

East China ◽

The East China Sea ◽

Vertical Wavelength ◽

China Sea ◽

Shelf Slope ◽

Continental Shelf Slope ◽

Parametric Subharmonic Instability

AbstractOn the basis of measurements from an observing mooring system, the observational evidence of parametric subharmonic instability (PSI) that transfers energy from semidiurnal internal tides (ITs) to the subharmonic waves at the East China Sea continental shelf slope is presented for the first time. Although the mooring station is very close to the energetic semidiurnal IT generation site, about 76% of the observed shear variance is contained in the near-inertial band, which is found to have comparable upward- and downward-propagating energy components. Bispectra and bicoherence estimates further confirm the occurrence of PSI transferring energy from the low-mode M2 ITs (vertical wavelength of ~1000 m) to high-mode subharmonic waves (vertical wavelength of ~200 m). The calculated energy transfer rate reveals an averaged net value of ~5 × 10−9 W kg−1. Strong temporal variation of is found that is not exactly in phase with the semidiurnal energy flux. After looking into the local vorticity fields, it is strongly suggested that the varying background relative vorticity associated with the evolving Kuroshio has modified the efficiency of PSI at the mooring location through changing the local effective inertial frequency.

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Observation of Semi-diurnal Internal Tides and Near-inertial Waves at the Shelf Break of the East China Sea

Ocean and Polar Research ◽

10.4217/opr.2011.33.4.409 ◽

2011 ◽

Vol 33 (4) ◽

pp. 409-419 ◽

Cited By ~ 2

Author(s):

Jae-Hun Park ◽

Heung-Jae Lie ◽

Binghuo Guo

Keyword(s):

East China Sea ◽

Shelf Break ◽

Internal Tides ◽

East China ◽

Inertial Waves ◽

The East China Sea ◽

China Sea

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Observation of internal tides in the East China Sea with an underwater sliding vehicle

Journal of Geophysical Research Atmospheres ◽

10.1029/95jc00473 ◽

1995 ◽

Vol 100 (C6) ◽

pp. 10801 ◽

Cited By ~ 13

Author(s):

Yoshifumi Kuroda ◽

Humio Mitsudera

Keyword(s):

East China Sea ◽

Internal Tides ◽

East China ◽

The East China Sea ◽

China Sea

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Variation of Internal Tides on the Continental Slope of the Southeastern East China Sea

Journal of Marine Science and Engineering ◽

10.3390/jmse10010104 ◽

2022 ◽

Vol 10 (1) ◽

pp. 104

Author(s):

Bing Yang ◽

Po Hu ◽

Yijun Hou

Keyword(s):

Continental Slope ◽

East China Sea ◽

Kuroshio Current ◽

Internal Tides ◽

East China ◽

Altimeter Data ◽

China Sea ◽

Second Mode ◽

Variance Contribution ◽

The Kuroshio

The semidiurnal internal tides (ITs) on the continental slope of the southeastern East China Sea (ECS) exhibited abrupt enhancement in November of 2017. This enhancement resulted from the intensification of the coherent semidiurnal ITs. Coherent and incoherent semidiurnal ITs had a comparative energy contribution in October; however, coherent semidiurnal ITs dominated with a variance contribution of 90% in November. The variance contribution of vertical modes of the semidiurnal ITs varied between October and November, and the mode with most variance contribution changed from the second mode to the first mode. Altimeter data and the observed background currents indicated that the Kuroshio mainstream meandered and abruptly intruded into the ECS in November. The upper layer background currents were significantly related to the kinetic energy of the semidiurnal ITs, and the correlation coefficient between them reached 0.81. The frequent occurrences of the Kuroshio intrusion have suggested that the ITs in the ECS are susceptible to the modulation of the Kuroshio current. Numerical modeling and predication of ITs should consider the meander of the Kuroshio mainstream.

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