scholarly journals Modulation of Internal Tides by Turbulent Mixing in the South China Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Bingtian Li ◽  
Libin Du ◽  
Shiqiu Peng ◽  
Yibo Yuan ◽  
Xiangqian Meng ◽  
...  
Keyword(s):  
South China Sea ◽  
Energy Budget ◽  
South China ◽  
Turbulent Mixing ◽  
Tidal Energy ◽  
The South China Sea ◽  
Internal Tides ◽  
Nonlinear Interactions ◽  
Mixing Intensity ◽  
O 10

Modulations of internal tides (ITs) including the baroclinic tidal energy budget, the incoherency, and the nonlinear interactions among different tidal components by turbulent mixing in the South China Sea (SCS) are investigated through numerical simulations. The baroclinic tidal energy budget can hardly be affected by the structure of mixing. Meanwhile, change in the mixing intensity in a reasonable range also cannot obviously modulate the baroclinic tidal energy budget in the SCS. Compared to the baroclinic energy budget, the distributions of conversion and dissipation are more sensitive to the change of mixing. Turbulent mixing also modulates the incoherency of ITs by changing the horizontal density in the ocean. The horizontal variation of density adds incoherence to ITs largely by affecting the internal tidal amplitudes. Furthermore, nonlinear interactions among different components of ITs are generally modulated by the mixing intensity, whereas the variation of the mixing structure can hardly influence the nonlinear interactions. Therefore, the diapycnal diffusivity can set to be horizontally and vertically homogeneous in most of the internal tidal simulations, except for those in which the incoherency of ITs needs to be simulated. However, excessive strong mixing will destroy the stratification. Thus, the optimum range for IT simulations in the SCS is from O (10–5) to O (10–3) m2s–1.

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>

scholarly journals Speed and Evolution of Nonlinear Internal Waves Transiting the South China Sea

2010 ◽  
Vol 40 (6) ◽  
pp. 1338-1355 ◽  
Author(s):  
Matthew H. Alford ◽  
Ren-Chieh Lien ◽  
Harper Simmons ◽  
Jody Klymak ◽  
Steve Ramp ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Slope ◽  
Internal Waves ◽  
South China ◽  
The South China Sea ◽  
Internal Tides ◽  
Deep Basin ◽  
Nonlinear Internal Waves ◽  
The Waves ◽  
Upper Slope

Abstract In the South China Sea (SCS), 14 nonlinear internal waves are detected as they transit a synchronous array of 10 moorings spanning the waves’ generation site at Luzon Strait, through the deep basin, and onto the upper continental slope 560 km to the west. Their arrival time, speed, width, energy, amplitude, and number of trailing waves are monitored. Waves occur twice daily in a particular pattern where larger, narrower “A” waves alternate with wider, smaller “B” waves. Waves begin as broad internal tides close to Luzon Strait’s two ridges, steepening to O(3–10 km) wide in the deep basin and O(200–300 m) on the upper slope. Nearly all waves eventually develop wave trains, with larger–steeper waves developing them earlier and in greater numbers. The B waves in the deep basin begin at a mean speed of ≈5% greater than the linear mode-1 phase speed for semidiurnal internal waves (computed using climatological and in situ stratification). The A waves travel ≈5%–10% faster than B waves until they reach the continental slope, presumably because of their greater amplitude. On the upper continental slope, all waves speed up relative to linear values, but B waves now travel 8%–12% faster than A waves, in spite of being smaller. Solutions of the Taylor–Goldstein equation with observed currents demonstrate that the B waves’ faster speed is a result of modulation of the background currents by an energetic diurnal internal tide on the upper slope. Attempts to ascertain the phase of the barotropic tide at which the waves were generated yielded inconsistent results, possibly partly because of contamination at the easternmost mooring by eastward signals generated at Luzon Strait’s western ridge. These results present a coherent picture of the transbasin evolution of the waves but underscore the need to better understand their generation, the nature of their nonlinearity, and propagation through a time-variable background flow, which includes the internal tides.

scholarly journals Long-range propagation and associated variability of internal tides in the South China Sea

2016 ◽  
Vol 121 (11) ◽  
pp. 8268-8286 ◽  
Author(s):  
Zhenhua Xu ◽  
Kun Liu ◽  
Baoshu Yin ◽  
Zhongxiang Zhao ◽  
Yang Wang ◽  
...  
Keyword(s):  
South China Sea ◽  
Long Range ◽  
South China ◽  
The South China Sea ◽  
Internal Tides ◽  
The South ◽  
China Sea

scholarly journals Determination of Harmonic Parameters with Temporal Variations: An Enhanced Harmonic Analysis Algorithm and Application to Internal Tidal Currents in the South China Sea

2018 ◽  
Vol 35 (7) ◽  
pp. 1375-1398 ◽  
Author(s):  
Guangzhen Jin ◽  
Haidong Pan ◽  
Qilin Zhang ◽  
Xianqing Lv ◽  
Wei Zhao ◽  
...  
Keyword(s):  
South China Sea ◽  
Harmonic Analysis ◽  
South China ◽  
Spline Interpolation ◽  
Temporal Variations ◽  
Tidal Currents ◽  
The South China Sea ◽  
Internal Tides ◽  
The South ◽  
China Sea

AbstractAs an effective tool to distinguish different tidal components, classical tidal current harmonic analysis has been widely used to obtain harmonic parameters of internal tidal currents. However, harmonic parameters cannot exactly reveal the motion of internal tides, as the irregular temporal variations for internal tides are significant in many regions of the world’s oceans. An enhanced harmonic analysis (EHA) algorithm based on the independent point scheme and cubic spline interpolation is presented in this paper to obtain harmonic parameters with temporal variations for different tidal constituents of internal tides. Moreover, this algorithm is applied to analyze 14 months of current data obtained from a mooring located on the continental shelf in the northeastern region of the South China Sea. The obvious irregular temporal variations for the four principal constituents—M2, K1, S2, and O1—of internal tides in this region are indicated. It is hoped that this algorithm might present a brand-new view for researchers to investigate the irregular temporal motions of internal tides.

scholarly journals Influence of Remote Internal Tides on the Locally Generated Internal Tides upon the Continental Slope in the South China Sea

2021 ◽  
Vol 9 (11) ◽  
pp. 1268
Author(s):  
Zheng Guo ◽  
Anzhou Cao ◽  
Shuya Wang
Keyword(s):  
South China Sea ◽  
Continental Slope ◽  
South China ◽  
Maximum Energy ◽  
The South China Sea ◽  
Internal Tides ◽  
The South ◽  
China Sea ◽  
The Taiwan Strait ◽  
Local Generation

In this paper, the M2 internal tides (ITs) originating from the continental slope in the South China Sea are studied using the CROCO model. The simulation results show that there are two origins of ITs on the continental slope: at 118°–119.5° E along 22° N near the southern entrance of the Taiwan Strait and at 117°–118° E along 20° N near Dongsha Island. The local generation of ITs is greatly influenced by the ITs that radiate from the Luzon Strait (LS). The integrated conversion at the first generation site is increased by 31% to 0.42 GW compared to the case where the LS is excluded from the simulation region. Its maximum energy flux almost doubles to 2.5 kW/m, which is 10% of the westward component. The existence of the other IT beams from Dongsha Island is attributed to the ITs from the LS. The local generation on the continental slope changes when remotely generated ITs alter the amplitudes and phases of the bottom pressure perturbation. These results indicate that the ITs originating from the LS contribute to the spatial variation of ITs in the SCS by modulating the IT generation on the continental slope.

scholarly journals Kinetic Energy Budget during the Genesis Period of Tropical Cyclone Durian (2001) in the South China Sea

2016 ◽  
Vol 144 (8) ◽  
pp. 2831-2854 ◽  
Author(s):  
Yaping Wang ◽  
Xiaopeng Cui ◽  
Xiaofan Li ◽  
Wenlong Zhang ◽  
Yongjie Huang
Keyword(s):  
Tropical Cyclone ◽  
Kinetic Energy ◽  
South China Sea ◽  
Latent Heat ◽  
Energy Budget ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
China Sea ◽  
Stage Stage

Abstract A set of kinetic energy (KE) budget equations associated with four horizontal flow components was derived to study the KE characteristics during the genesis of Tropical Cyclone (TC) Durian (2001) in the South China Sea using numerical simulation data. The genesis process was divided into three stages: the monsoon trough stage (stage 1), the midlevel mesoscale convective vortex (MCV) stage (stage 2), and the establishment stage of the TC vortex (stage 3). Analysis showed that the KE of the symmetric rotational flow (SRF) was the largest and kept increasing, especially in stages 2 and 3, representing the symmetrization process during TC genesis. The KE of the SRF was mainly converted from the KE of the symmetric divergent flow (SDF), largely transformed from the available potential energy (APE). It was found that vortical hot towers (VHTs) emerged abundantly, aggregated, and merged within the MCV region in stages 1 and 2. From the energy budget perspective, massive moist-convection-produced latent heat was concentrated and accumulated within the MCV region, especially in stage 2, and further warmed the atmosphere, benefiting the accumulation of APE and the transformation from APE to KE. As a result, the midlevel circulation (or MCV) grew strong rapidly. In stage 3, the intensity and number of VHTs both decreased. However, affected by increasing lower-level inward radial wind, latent heat released by the organized convection, instead of disorganized VHTs in the first two stages, continuously contributed to the strengthening of the surface TC circulation as well as the warm core.

scholarly journals Circulation Driven by Multihump Turbulent Mixing Over a Seamount in the South China Sea

2022 ◽  
Vol 8 ◽  
Author(s):  
Ruijie Ye ◽  
Xiaodong Shang ◽  
Wei Zhao ◽  
Chun Zhou ◽  
Qingxuan Yang ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Deep Water ◽  
Turbulent Mixing ◽  
Three Dimensional ◽  
The South China Sea ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
China Sea ◽  
Meridional Overturning

Turbulent mixing above rough topography is crucial for the vertical motions of deep water and the closure of the meridional overturning circulation. Related to prominent topographic features, turbulent mixing not only exhibits a bottom-intensified vertical structure but also displays substantial lateral variation. How turbulent mixing varies in the upslope direction and its impact on the upwelling of deep water over sloping topography remains poorly understood. In this study, the notable multihump structure of the bottom-intensified turbulent diffusivity in the upslope direction of a seamount in the South China Sea (SCS) is revealed by full-depth fine-resolution microstructure and hydrographic profiles. Numerical experiments indicate that multihump bottom-intensified turbulent mixing around a seamount could lead to multiple cells of locally strengthened circulations consisting of upwelling (downwelling) motions in (above) the bottom boundary layer (BBL) that are induced by bottom convergence (divergence) of the turbulent buoyancy flux. Accompanied by cyclonic (anticyclonic) flow, a three-dimensional spiral circulation manifests around the seamount topography. These findings regarding the turbulent mixing and three-dimensional circulation around a deep seamount provide support for the further interpretation of the abyssal meridional overturning circulation.

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.

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