Observations of parametric subharmonic instability of the diurnal internal tide in the South China Sea

2008 ◽  
Vol 35 (15) ◽  
Author(s):  
M. H. Alford
Keyword(s):  
South China Sea ◽  
South China ◽  
Internal Tide ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Parametric Subharmonic Instability

Disintegration of the K1 internal tide in the South China Sea due to parametric subharmonic instability

2021 ◽  
Author(s):  
Kun Liu ◽  
Zhongxiang Zhao
Keyword(s):  
South China Sea ◽  
South China ◽  
Internal Tide ◽  
The South China Sea ◽  
Internal Tides ◽  
Upper Ocean ◽  
The South ◽  
China Sea ◽  
Parametric Subharmonic Instability ◽  
Critical Latitude

<p>The disintegration of the equatorward-propagating K<sub>1</sub> internal tide in the South China Sea (SCS) by parametric subharmonic instability (PSI) at its critical latitude of 14.52ºN is investigated numerically. The multiple-source generation and long-range propagation of K<sub>1</sub> internal tides are successfully reproduced. Using equilibrium analysis, the internal wave field near the critical latitude is found to experience two quasi-steady states, between which the subharmonic waves develop constantly. The simulated subharmonic waves agree well with classic PSI theoretical prediction. The PSI-induced near-inertial waves are of half the K<sub>1</sub> frequency and dominantly high modes, the vertical scales ranging from 50 to 180 m in the upper ocean. From an energy perspective, PSI mainly occurs in the critical latitudinal zone from 13–15ºN. In this zone, the incident internal tide loses ~14% energy in the mature state of PSI. PSI triggers a mixing elevation of O(10<sup>-5</sup>–10<sup>-4</sup> m<sup>2</sup>/s) in the upper ocean at the critical latitude, which is several times larger than the background value. The contribution of PSI to the internal tide energy loss and associated enhanced mixing may differ regionally and is closely dependent on the intensity and duration of background internal tide. The results elucidate the far-field dissipation mechanism by PSI in connecting interior mixing with remotely generated K<sub>1</sub> internal tides in the Luzon Strait.</p>

Disintegration of the K1 Internal Tide in the South China Sea due to Parametric Subharmonic Instability

2020 ◽  
Vol 50 (12) ◽  
pp. 3605-3622
Author(s):  
Kun Liu ◽  
Zhongxiang Zhao
Keyword(s):  
South China Sea ◽  
South China ◽  
Internal Tide ◽  
The South China Sea ◽  
Internal Tides ◽  
Upper Ocean ◽  
The South ◽  
China Sea ◽  
Parametric Subharmonic Instability ◽  
Critical Latitude

AbstractThe disintegration of the equatorward-propagating K1 internal tide in the South China Sea (SCS) by parametric subharmonic instability (PSI) at its critical latitude of 14.52°N is investigated numerically. The multiple-source generation and long-range propagation of K1 internal tides are successfully reproduced. Using equilibrium analysis, the internal wave field near the critical latitude is found to experience two quasi-steady states, between which the subharmonic waves develop constantly. The simulated subharmonic waves agree well with classic PSI theoretical prediction. The PSI-induced near-inertial waves are of half the K1 frequency and dominantly high modes, the vertical scales ranging from 50 to 180 m in the upper ocean. From an energy perspective, PSI mainly occurs in the critical latitudinal zone from 13° to 15°N. In this zone, the incident internal tide loses ~14% energy in the mature state of PSI. PSI triggers a mixing elevation of O(10−5–10−4) m2 s−1 in the upper ocean at the critical latitude, which is several times larger than the background value. The contribution of PSI to the internal tide energy loss and associated enhanced mixing may differ regionally and is closely dependent on the intensity and duration of background internal tide. The results elucidate the far-field dissipation mechanism by PSI in connecting interior mixing with remotely generated K1 internal tides in the Luzon Strait.

scholarly journals Three-Dimensional Distribution of Turbulent Mixing in the South China Sea

2016 ◽  
Vol 46 (3) ◽  
pp. 769-788 ◽  
Author(s):  
Qingxuan Yang ◽  
Wei Zhao ◽  
Xinfeng Liang ◽  
Jiwei Tian
Keyword(s):  
South China Sea ◽  
South China ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
Internal Tide ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Dimensional Distribution ◽  
First Time

AbstractA three-dimensional distribution of turbulent mixing in the South China Sea (SCS) is obtained for the first time, using the Gregg–Henyey–Polzin parameterization and hydrographic observations from 2005 to 2012. Results indicate that turbulent mixing generally increases with depth in the SCS, reaching the order of 10−2 m2 s−1 at depth. In the horizontal direction, turbulence is more active in the northern SCS than in the south and is more active in the east than the west. Two mixing “hotspots” are identified in the bottom water of the Luzon Strait and Zhongsha Island Chain area, where diapycnal diffusivity values are around 3 × 10−2 m2 s−1. Potential mechanisms responsible for these spatial patterns are discussed, which include internal tide, bottom bathymetry, and near-inertial energy.

scholarly journals The Generation and Evolution of Nonlinear Internal Waves in the Deep Basin of the South China Sea

2011 ◽  
Vol 41 (7) ◽  
pp. 1345-1363 ◽  
Author(s):  
Qiang Li ◽  
David M. Farmer
Keyword(s):  
South China Sea ◽  
Internal Waves ◽  
South China ◽  
Internal Tide ◽  
Luzon Strait ◽  
The South China Sea ◽  
The South ◽  
Deep Basin ◽  
Nonlinear Internal Waves ◽  
China Sea

Abstract Time series observations of nonlinear internal waves in the deep basin of the South China Sea are used to evaluate mechanisms for their generation and evolution. Internal tides are generated by tidal currents over ridges in Luzon Strait and steepen as they travel west, subsequently generating high-frequency nonlinear waves. Although nonlinear internal waves appear repeatedly on the western slopes of the South China Sea, their appearance in the deep basin is intermittent and more closely related to the amplitude of the semidiurnal than the predominant diurnal tidal current in Luzon Strait. As the internal tide propagates westward, it evolves under the influence of nonlinearity, rotation, and nonhydrostatic dispersion. The interaction between nonlinearity and rotation transforms the internal tide into a parabolic or corner shape. A fully nonlinear two-layer internal wave model explains the observed characteristics of internal tide evolution in the deep basin for different representative forcing conditions and allows assessment of differences between the fully and weakly nonlinear descriptions. Matching this model to a wave generation solution for representative topography in Luzon Strait leads to predictions in the deep basin consistent with observations. Separation of the eastern and western ridges is close to the internal semidiurnal tidal wavelength, contributing to intensification of the westward propagating semidiurnal component. Doppler effects of internal tide generation, when combined with a steady background flow, suggest an explanation for the apparent suppression of nonlinear wave generation during periods of westward intrusion of the Kuroshio.

scholarly journals Tidal Mixing in the South China Sea: An Estimate Based on the Internal Tide Energetics

2016 ◽  
Vol 46 (1) ◽  
pp. 107-124 ◽  
Author(s):  
Xiaowei Wang ◽  
Shiqiu Peng ◽  
Zhiyu Liu ◽  
Rui Xin Huang ◽  
Yu-Kun Qian ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Dissipation Rate ◽  
Internal Tide ◽  
The South China Sea ◽  
Internal Tides ◽  
Tidal Mixing ◽  
The South ◽  
China Sea ◽  
Diapycnal Diffusivity

AbstractBy taking into account the contributions of both locally and remotely generated internal tides, the tidal mixing in the Luzon Strait (LS) and the South China Sea (SCS) is investigated through internal-tide simulation and energetics analysis. A three-dimensional nonhydrostatic high-resolution model driven by four primary tidal constituents (M2, S2, K1, and O1) is used for the internal-tide simulation. The baroclinic energy budget analysis reveals that the internal tides radiated from the LS are the dominant energy source for the tidal dissipation in the SCS. In the LS, the estimated depth-integrated turbulent kinetic energy dissipation exceeds O(1) W m−2 atop the two subsurface ridges, with a dissipation rate of >O(10−7) W kg−1 and diapycnal diffusivity of ~O(10−2) m2 s−1. In the SCS, the most intense turbulence occurs in the deep-water basin with a dissipation rate of O(10−8–10−6) W kg−1 and diapycnal diffusivity of O(10−3–10−1) m2 s−1 within the ~2000-m water column above the seafloor as well as in the shelfbreak region with a dissipation rate of O(10−7–10−6) W kg−1 and diapycnal diffusivity of O(10−4–10−3) m2 s−1. These estimated values are consistent with observations reported in previous studies and are at least one order of magnitude larger than those based solely on locally generated internal tides.

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