Role of surface winds in SAR signatures of oceanic internal waves in the northern South China Sea

Huang, Weigen; Gan, Xilin; Yang, Jingsong; Fu, Bin; Chen, Peng

doi:10.1117/12.829874

Cited by 4 publications

(4 citation statements)

References 7 publications

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“…Thus, the phenomenon in which the discernable ISW signatures appear in only some ASAR wide‐swath images is related to various factors. Figure presents the seasonal variations of the ISWs from the 61 ASAR wide‐swath images, which are consistent with previous findings (Huang et al, ) that the occurrence of the ISWs is more frequent in summer than other seasons in the SCS. This situation is partly because a strong thermocline is known to be present in summer.…”

Section: Sar Observations Of Isw Refraction and Reconnection Behind Tsupporting

confidence: 90%

SAR Observation and Numerical Simulation of Internal Solitary Wave Refraction and Reconnection Behind the Dongsha Atoll

Jia

Liang

et al. 2018

JGR Oceans

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The refraction and reconnection of internal solitary waves (ISWs) around the Dongsha Atoll (DSA) in the northern South China Sea (SCS) are investigated based on spaceborne synthetic aperture radar (SAR) observations and numerical simulations. In general, a long ISW front propagating from the deep basin of the northern SCS splits into northern and southern branches when it passes the DSA. In this study, the statistics of Envisat Advanced SAR (ASAR) images show that the northern and southern wave branches can reconnect behind the DSA, but the reconnection location varies. A previously developed nonlinear refraction model is set up to simulate the refraction and reconnection of the ISWs behind the DSA, and the model is used to evaluate the effects of ocean stratification, background currents, and incoming ISW characteristics at the DSA on the variation in reconnection locations. The results of the first realistic simulation agree with consecutive TerraSAR‐X (TSX) images captured within 12 h of each other. Further sensitivity simulations show that ocean stratification, background currents, and initial wave amplitudes all affect the phase speeds of wave branches and therefore shift their reconnection locations while shapes and locations of incoming wave branches upstream of the DSA profoundly influence the subsequent propagation paths. This study clarifies the variation in reconnection locations of ISWs downstream of the DSA and reveals the important mechanisms governing the reconnection process, which can improve our understanding of the propagation of ISWs near the DSA.

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Section: Sar Observations Of Isw Refraction and Reconnection Behind Tsupporting

confidence: 90%

SAR Observation and Numerical Simulation of Internal Solitary Wave Refraction and Reconnection Behind the Dongsha Atoll

Jia

Liang

et al. 2018

JGR Oceans

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“…The largest ISW caused strong currents which had the maximum westward velocity and the maximum northward velocity both exceeding 40 cm/s inside the bore (Figures c and d). The propagation directions of the ISWs were in agreement with the previous observations from remote sensing and mooring (Figure d) [ Fang et al ., ; Cai et al ., ; Duda et al ., ; Huang et al ., ; Ramp et al ., ; Wang et al ., ].…”

Section: Resultsmentioning

confidence: 99%

“…The northern South China Sea provides prominent examples of internal waves including the largest ones in the world [ Ramp et al ., ], thus becoming a natural laboratory to study the interaction between internal waves and seabed. Here, ubiquitous internal waves are believed to generate from the Luzon Strait and propagate westward to shoal, break, or refract near Dongsha Atoll basing on models, remote sensing data, and in situ mooring observations [ Hsu et al ., ; Orr and Mignerey , ; Duda et al ., ; Liu and Hsu , ; Zhao and Alford , ; Ramp et al ., ; Huang et al ., ; Farmer et al ., ; Fu et al ., ; Guo et al ., ; Wang et al ., ; Alford et al ., ]. However, few cases of internal waves west of Dongsha Atoll were focused [ Cai et al ., ; Ramp et al ., ], probably because most of their energy would dissipate through shoaling or breaking on the shelf or slope [ Alford et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Footprints of obliquely incident internal solitary waves and internal tides near the shelf break in the northern South China Sea

Yan

Hou

et al. 2016

J. Geophys. Res. Oceans

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A mooring system and two sites of bottom currents were deployed over the slope and near the shelf break on the propagating paths of internal solitary waves (ISWs), west off Dongsha Atoll in the northern South China Sea. Data indicated that energetic ISWs obliquely shoaled onto the shelf west off Dongsha Atoll in an approximately 290° direction, causing strong reversing currents (some exceeding 80 cm/s) near the bottom. Two types of sandwaves and short scour channels are discernible on the seafloor near the shelf break, which have reasonable correlations with the obliquely incident ISWs and internal tides. Type 1 sandwaves, featured by ISWs at the depths of 130–150 m, have flat crests interacting with the isobaths at an angle of nearly 45° which slightly incline and migrate upslope. Type 2 sandwaves are associated with internal tides, which have crests parallel to the isobaths and distinctly incline and migrate downslope. Short channels are parallel to the depth contours and truncate the strata, which could be formed and maintained by along‐slope currents that are probably produced by the obliquely ISWs on a large gradient (γ > 0.8°). The ISWs can move coarse grains or suspend fine grains but do not change the long‐term trend of sediment transport on the seabed with larger gradients (γ/c > 1), which is dominated by internal tides. These features are likely widespread near the shelf break in the northern South China Sea and other seas but are limited on mild slopes where ISWs do not break.

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“…Based on Huang et al (2008), the generation of ISWs exhibits seasonal variation with more occurrences in the northern South China Sea during summer. This is due to the stronger vertical stratification in summer, which favors the westward propagation of the internal waves in the Luzon Strait.…”

Section: Model Setupmentioning

confidence: 99%

Three-dimensional numerical simulations of oblique internal solitary wave-wave interactions in the South China Sea

Jia,

Gong,

Zhang

et al. 2024

Front. Mar. Sci.

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Satellite images show that the oblique internal solitary wave-wave interactions frequently occur in the South China Sea, especially in the periphery of Dongsha Island. Depending on the amplitudes and angles of initial oblique waves, theoretical works illustrated that the evolution pattern falls into different regimes characterised by the respective four-fold augmentation of wave amplitudes (relative to the initial waves) and occurrence of Mach stem waves in the interaction region. Nevertheless, these results were based on the reduced theories rooted from the primitive Navier-Stokes equations and the disparities induced by these simplifications with the scenarios in realistic ocean are still unclear. To fill this research gap, three-dimensional numerical simulations in the South China Sea are used to evaluate the oblique internal solitary wave-wave interactions. It is found that transformations between mode-1 and mode-2 waves occur near the Dongsha Island when two waves obliquely collide, together with a small portion of energy is converted into higher modes, most of which is dissipated locally due to their unstable vertical structures. This conclusion has been seldom reported in previous studies (if any). These oblique interactions are essentially nonlinear and impacted by the dynamical factors, such as varying depth, background current, etc., exhibiting complicated variations of waveforms and energy, which, further, enhance the mixing at local sites in the mechanism of both shear and convective instabilities indicated by the Richardson number.

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Role of surface winds in SAR signatures of oceanic internal waves in the northern South China Sea

Cited by 4 publications

References 7 publications

SAR Observation and Numerical Simulation of Internal Solitary Wave Refraction and Reconnection Behind the Dongsha Atoll

SAR Observation and Numerical Simulation of Internal Solitary Wave Refraction and Reconnection Behind the Dongsha Atoll

Footprints of obliquely incident internal solitary waves and internal tides near the shelf break in the northern South China Sea

Three-dimensional numerical simulations of oblique internal solitary wave-wave interactions in the South China Sea

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