Tang Tswen Yung

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Tang
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Tswen Yung
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Article

Acoustic intensity fluctuations induced by South China Sea internal tides and solitons

2004-10 , Chiu, Ching-Sang , Ramp, Steven R. , Miller, Christopher W. , Lynch, James F. , Duda, Timothy F. , Tang, Tswen Yung

Between late April and May 23, 2001, a suite of acoustic and oceanographic sensors was deployed by a team of U.S., Taiwan, and Singapore scientists in the northeastern South China Sea to study the effects of ocean variability on low-frequency sound propagation in a shelfbreak environment. The primary acoustic receiver was an L-shaped hydrophone array moored on the continental shelf that monitored a variety of signals transmitted along and across the shelfbreak by moored sources. This paper discusses and contrasts the fluctuations in the 400-Hz signals transmitted across the shelfbreak and measured by the vertical segment of the listening array on two different days, one with the passage of several huge solitons that depressed the shallow isotherms to near the sea bottom and one with a much less energetic internal wavefield. In addition to exhibiting large and rapid temporal changes, the acoustic data show a much more vertically diffused sound intensity field as the huge solitons occupied and passed through the transmission path. Using a space-time continuous empirical sound-speed model based on the moored temperature records, the observed acoustic intensity fluctuations are explained using coupled-mode physics.

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Article

Barotropic tide in the northeast South China Sea

2004-10 , Beardsley, Robert C. , Duda, Timothy F. , Lynch, James F. , Irish, James D. , Ramp, Steven R. , Chiu, Ching-Sang , Tang, Tswen Yung , Yang, Yiing-Jang , Fang, Guohong

A moored array deployed across the shelf break in the northeast South China Sea during April-May 2001 collected sufficient current and pressure data to allow estimation of the barotropic tidal currents and energy fluxes at five sites ranging in depth from 350 to 71 m. The tidal currents in this area were mixed, with the diurnal O1 and K1 currents dominant over the upper slope and the semidiurnal M2 current dominant over the shelf. The semidiurnal S2 current also increased onshelf (northward), but was always weaker than O1 and K1. The tidal currents were elliptical at all sites, with clockwise turning with time. The O1 and K1 transports decreased monotonically northward by a factor of 2 onto the shelf, with energy fluxes directed roughly westward over the slope and eastward over the shelf. The M2 and S2 current ellipses turned clockwise and increased in amplitude northward onto the shelf. The M2 and S2 transport ellipses also exhibited clockwise veering but little change in amplitude, suggesting roughly nondivergent flow in the direction of major axis orientation. The M2 energy flux was generally aligned with the transport major axis with little phase lag between high water and maximum transport. These barotropic energy fluxes are compared with the locally generated diurnal internal tide and high-frequency internal solitary-type waves generated by the M2 flow through the Luzon Strait.

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Article

Internal tide and nonlinear internal wave behavior at the continental slope in the northern south China Sea

2004-10 , Duda, Timothy F. , Lynch, James F. , Irish, James D. , Beardsley, Robert C. , Ramp, Steven R. , Chiu, Ching-Sang , Tang, Tswen Yung , Yang, Yiing-Jang

A field program to measure acoustic propagation characteristics and physical oceanography was undertaken in April and May 2001 in the northern South China Sea. Fluctuating ocean properties were measured with 21 moorings in water of 350- to 71-m depth near the continental slope. The sea floor at the site is gradually sloped at depths less than 90 m, but the deeper area is steppy, having gradual slopes over large areas that are near critical for diurnal internal waves and steep steps between those areas that account for much of the depth change. Large-amplitude nonlinear internal gravity waves incident on the site from the east were observed to change amplitude, horizontal length scale, and energy when shoaling. Beginning as relatively narrow solitary waves of depression, these waves continued onto the shelf much broadened in horizontal scale, where they were trailed by numerous waves of elevation (alternatively described as oscillations) that first appeared in the continental slope region. Internal gravity waves of both diurnal and semidiurnal tidal frequencies (internal tides) were also observed to propagate into shallow water from deeper water, with the diurnal waves dominating. The internal tides were at times sufficiently nonlinear to break down into bores and groups of high-frequency nonlinear internal waves.

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Preprint

The formation and fate of internal waves in the South China Sea

2015-03 , Alford, Matthew H. , Peacock, Thomas , MacKinnon, Jennifer A. , Nash, Jonathan D. , Buijsman, Maarten C. , Centurioni, Luca R. , Chao, Shenn-Yu , Chang, Ming-Huei , Farmer, David M. , Fringer, Oliver B. , Fu, Ke-Hsien , Gallacher, Patrick C. , Graber, Hans C. , Helfrich, Karl R. , Jachec, Steven M. , Jackson, Christopher R. , Klymak, Jody M. , Ko, Dong S. , Jan, Sen , Johnston, T. M. Shaun , Legg, Sonya , Lee, I-Huan , Lien, Ren-Chieh , Mercier, Matthieu J. , Moum, James N. , Musgrave, Ruth C. , Park, Jae-Hun , Pickering, Andrew I. , Pinkel, Robert , Rainville, Luc , Ramp, Steven R. , Rudnick, Daniel L. , Sarkar, Sutanu , Scotti, Alberto , Simmons, Harper L. , St Laurent, Louis C. , Venayagamoorthy, Subhas K. , Wang, Yu-Huai , Wang, Joe , Yang, Yiing-Jang , Paluszkiewicz, Theresa , Tang, Tswen Yung

Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they impact a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for manmade structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, posing severe challenges for their observation and their inclusion in numerical climate models, which are sensitive to their effects6-7. Over a decade of studies8-11 have targeted the South China Sea, where the oceans’ most powerful internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their generation mechanism, variability and energy budget, however, due to the lack of in-situ data from the Luzon Strait, where extreme flow conditions make measurements challenging. Here we employ new observations and numerical models to (i) show that the waves begin as sinusoidal disturbances rather than from sharp hydraulic phenomena, (ii) reveal the existence of >200-m-high breaking internal waves in the generation region that give rise to turbulence levels >10,000 times that in the open ocean, (iii) determine that the Kuroshio western boundary current significantly refracts the internal wave field emanating from the Luzon Strait, and (iv) demonstrate a factor-of-two agreement between modelled and observed energy fluxes that enables the first observationally-supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions.

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Article

Turbulent properties of internal waves in the South China Sea

2011-12 , St. Laurent, Louis C. , Simmons, Harper L. , Tang, Tswen Yung , Wang, YuHuai

Luzon Strait and South China Sea waters are among the most energetic internal wave environments in the global ocean. Strong tides and stratification in Luzon Strait give rise to internal waves that propagate west into the South China Sea. The energy carried by the waves is dissipated via turbulent processes. Here, we present and contrast the relatively few direct observations of turbulent dissipation in South China Sea internal waves. Frictional processes active in the bottom boundary layer dissipate some of the energy along China's continental shelf. It appears that more energy is lost in Taiwanese waters of the Dongsha Plateau, where the waves reach their maximum amplitudes, and where the bottom topography abruptly shoals from 3,000 m in the deep basin to 1,000 m and shallower on the plateau. There, energy dissipation by turbulence reaches 1 W m–2, on par with the conversion rates of Luzon Strait.

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Article

Typhoon-ocean interaction in the western North Pacific : Part 1

2011-12 , D'Asaro, Eric A. , Black, Peter G. , Centurioni, Luca R. , Harr, Patrick , Jayne, Steven R. , Lin, I.-I. , Lee, Craig M. , Morzel, Jan , Mrvaljevic, Rosalinda K. , Niiler, Pearn P. , Rainville, Luc , Sanford, Thomas B. , Tang, Tswen Yung

The application of new technologies has allowed oceanographers and meteorologists to study the ocean beneath typhoons in detail. Recent studies in the western Pacific Ocean reveal new insights into the influence of the ocean on typhoon intensity.

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Article

Internal solitons in the northeastern south China Sea. Part I: sources and deep water propagation

2004-10 , Ramp, Steven R. , Tang, Tswen Yung , Duda, Timothy F. , Lynch, James F. , Liu, Antony K. , Chiu, Ching-Sang , Bahr, Frederick L. , Kim, Hyoung-Rok , Yang, Yiing-Jang

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 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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Article

Research highlights from the Asian Seas International Acoustics Experiment in the South China Sea

2004-10 , Lynch, James F. , Ramp, Steven R. , Chiu, Ching-Sang , Tang, Tswen Yung , Yang, Yiing-Jang , Simmen, Jeffrey A.

The Asian Seas International Acoustics Experiment (ASIAEX) included two major field programs, one in the South China Sea (SCS) and the other in the East China Sea (ECS). This paper summarizes results from the work conducted during April and May 2000 and 2001 over the continental shelf and slope in the northeastern South China Sea, just east of Dongsha Island (Pratis Reef). The primary emphasis of the field program was on water-column variability and its impact on acoustic propagation loss. The reader is steered to the appropriate paper within this Special Issue when more information on a specific topic is desired.