Nonlinear Internal Waves in the South China Sea

Hsu, Meng−Kai; Liu, Antony K.

doi:10.1080/07038992.2000.10874757

Cited by 133 publications

(105 citation statements)

References 6 publications

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“…This suggestion was backed up by a RADARSAT-1 ScanSAR image taken on May 4, 1998. This image recorded three internal wave packets, two of them in deep waters contained depression waves and one in shallow waters contained elevation waves [Hsu and Liu, 2000]. The polarity conversions from depression ISWs to elevation ISWs on the South China Sea continental shelf were confirmed by shipboard acoustic flow visualization data in the Asian Seas International Acoustics Experiment (ASIAEX) [Orr and Mignerey, 2003].…”

Section: Introductionmentioning

confidence: 76%

Satellite observation of internal solitary waves converting polarity

Zhao

Klemas

Zheng

et al. 2003

Geophysical Research Letters

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[1] On a SPOT-3 visible image over the South China Sea continental shelf, two contrasting signatures of internal solitary waves (ISWs) are observed: darker stripes leading brighter stripes in the lower part, and brighter stripes leading darker stripes in the upper part. The authors suggest that the contrasting patterns are caused by ISWs of different polarities. A packet of ISWs is observed in the process of converting polarity due to bottom shoaling, both in the propagation direction and in the transect direction. The evolution process can be obtained by transferring information from the spatial domain to the temporal domain. The conversion process starts with the original depression ISWs passing the 160 m isobath. The evolution process can be divided into two phases: the first is the broadening of the original depression waves and the second is the appearance of the new-born elevation waves. These two phases are verified using numerical simulation.

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Section: Introductionmentioning

confidence: 76%

Satellite observation of internal solitary waves converting polarity

Zhao

Klemas

Zheng

et al. 2003

Geophysical Research Letters

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“…This is easily explained via the well known theory that when the upper-layer depth is thinner than the lower-layer depth (the usual deep water case) depression waves form, but when the upper layer is thicker than the lower layer, elevation waves form. Mathematically this occurs when the nonlinear parameter changes sign [7]. Clearly, the criterion for elevation waves was met during 0600-1800 hours when the thermocline was nearly on the bottom.…”

Section: Wave Transformation In Shallow Watermentioning

confidence: 99%

“…There are several small island groups within the Luzon strait, some of which have very small, shallow passages between islands. These islands do not appreciably inhibit the mass transport through the strait, but may be important to the local dynamics as the generation point for the internal solitons observed propagating across the northeastern corner of the sea [5]- [7]. In the northeast sector of the SCS, between the Luzon Strait and ASIAEX region, the central basin is more than 4000 m deep with no islands, banks, or other shallow spots in between.…”

Section: B Location and Basin Geometrymentioning

confidence: 99%

“…The South China Sea is no exception: Synthetic Aperture Radar (SAR) imagery [7], [15] and moored Doppler profilers and thermistor chains [5] and [6] have revealed strong nonlinear internal waves or solitons present in the northeastern SCS between Luzon Strait and the Chinese continental shelf, propagating slightly north of due west. The SCS pilot study moorings [16] clearly observed these motions, and they influenced the design of the moorings for the main field program.…”

Section: E Internal Wavesmentioning

confidence: 99%

See 1 more Smart Citation

Internal Solitons in the Northeastern South China Sea Part I: Sources and Deep Water Propagation

Ramp

Tang²,

Duda³

et al. 2004

IEEE J. Oceanic Eng.

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340

321

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Abstract-A moored array of current, temperature, conductivity, and pressure sensors was deployed across the Chinese continental shelf and slope in support of the Asian Seas International Acoustics Experiment. The goal of the observations was to quantify the water column variability in order to understand the along-and across-shore low-frequency acoustic propagation in shallow water. The moorings were deployed from April 21-May 19, 2001 and sampled at 1-5 min intervals to capture the full range of temporal variability without aliasing the internal wave field. The dominant oceanographic signal by far was in fact the highly nonlinear internal waves (or solitons) which were generated near the Batan Islands in the Luzon Strait and propagated 485 km across deep water to the observation region. Dubbed trans-basin waves, to distinguish them from other, smaller nonlinear waves generated locally near the shelf break, these waves had amplitudes ranging from 29 to greater than 140 m and were among the largest such waves ever observed in the world's oceans. The waves arrived at the most offshore mooring in two clusters lasting 7-8 days each separated by five days when no waves were observed. Within each cluster, two types of waves arrived which have been named type-a and type-b. The type-a waves had greater amplitude than the type-b waves and arrived with remarkable regularity at the same time each day, 24 h apart. The type-b waves were weaker than the type-a waves, arrived an hour later each day, and generally consisted of a single soliton growing out of the center of the wave packet. Comparison with modeled barotropic tides from the generation region revealed that: 1) The two clusters were generated around the time of the spring tides in the Luzon strait; and 2) The type-a waves were generated on the strong side of the diurnal inequality while the type-b waves were generated on the weaker beat. The position of the Kuroshio intrusion into the Luzon Strait may modulate the strength of the waves being produced. As the waves shoaled, the huge lead solitons first split into two solitons then merged together into a broad region of thermocline depression at depths less than 120 m. Elevation waves sprang up behind them as they continued to propagate onshore. The elevation waves also grew out of regions where the locally-generated internal tide forced the main thermocline down near the bottom. The "critical T. Y. Tang is with the Institute of Oceanography, National Taiwan University, Taipei, ROC.H. point" where the upper and lower layers were equal was a good indicator of when the depression or elevation waves would form, however this was not a static point, but rather varied in both space and time according to the presence or absence of the internal tides and the incoming trans-basin waves themselves.

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“…The terrain of the strait makes it an active ground for the generation of internal waves. Recently, dramatic internal tides, solitary waves and bores were observed at locations from LS to the northern South China Shelf (NSCS) both in satellite images and field observations Hsu & Liu, 2000;Liu et al, 2006Liu et al, , 2008Yang et al, 2004;Zhao, Klemas, Zheng, & Yan, 2004).…”

Section: Introductionmentioning

confidence: 99%

Current Observations of Internal Tides and Parametric Subharmonic Instability in Luzon Strait

et al. 2012

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Acoustic Doppler Current Profiler (ADCP) measurements of the velocity structure in the thermocline in Luzon Strait are presented. The statistics for current, vertical variation of the inertia-gravity waveband, parametric subharmonic instability (PSI), and current shear are analyzed. It was found that 1) barotropic flow primarily consists of a nearly circular mixed tide. Diurnal tides are strongest and show smooth variance with a fortnightly spring-neap cycle, indicative of the astronomical tide-generating force. However, the semi-diurnal band power exhibits a high-frequency oscillation as a result of non-linear interactions. The high-frequency band power with high values during the spring tide oscillates with the tidal cycle. Near-inertial wave motions showing random variance may be caused by changes in the wind forcing at the sea surface or by random forcing. 2) Baroclinic velocities exhibit strong shear structure. The observed large changes in the amplitude of the baroclinic velocity and the limited vertical extent of the high-velocity cores may be interpreted as internal wave beams that pass through the observed water column. Semi-diurnal tides are dominant in the baroclinic velocity. Kinetic energy spectra also revealed that additional peaks were centred at sum-tidal-inertial interaction frequencies (such as M 2 + f) and difference-interaction frequencies (such as M 2 − f). The spectral exponent of the baroclinic velocity is ω −α (1 < α < 3). 3) Strong non-linear interactions among internal waves exist, and the semi-diurnal (M 2 ) component plays a key role in these interactions. Bicoherence analysis showed that M 2 /2 waves were non-linearly coupled with the dominant M 2 internal tide. 4) The polarization relations were used to diagnose observational internal tidal motions. Diurnal waves propagate to the east-northeast, and the semi-diurnal-diurnal waves propagate westward. In the case of diurnal tides, the minor to major axis ratio is different from the expected value of f/ω K1 because of the deviation of inclinations, whereas, for semi-diurnal tides, it is close to the expected value of f/ω M2 at depths from 30 to 150 m.RÉSUMÉ [Traduit par la rédaction] Nous présentons les mesures de la structure des vitesses dans la thermocline faites par profileur de courant à effet Doppler (ADCP) dans le détroit de Luçon. Nous analysons les statistiques sur le courant, la variation verticale de la gamme d'ondes d'inertie-gravité, l'instabilité subharmonique paramétrique (PSI) et le cisaillement du courant. Il ressort que 1) l'écoulement barotrope consiste principalement en une marée mixte presque circulaire. Les marées diurnes sont les plus fortes et présentent une variance régulière dans un cycle vives-eaux mortes-eaux de deux semaines qui révèle la nature astronomique de la force qui produit les marées. Cependant, la puissance de bande semi-diurne affiche une oscillation de haute fréquence causée par des interactions non linéaires. La puissance de bande de haute fréquence avec des valeurs élevées durant les ...

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Nonlinear Internal Waves in the South China Sea

Cited by 133 publications

References 6 publications

Satellite observation of internal solitary waves converting polarity

Satellite observation of internal solitary waves converting polarity

Internal Solitons in the Northeastern South China Sea Part I: Sources and Deep Water Propagation

Current Observations of Internal Tides and Parametric Subharmonic Instability in Luzon Strait

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