Acoustic Intensity Fluctuations Induced by South China Sea Internal Tides and Solitons

Chiu, Ching‐Sang; Ramp, S.R.; Miller, Chris W.; Lynch, James F.; Duda, Timothy F.; Tang, Tie-Qiao

doi:10.1109/joe.2004.834173

Cited by 62 publications

(35 citation statements)

References 15 publications

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“…The acoustic signals were all received at an L-shaped hydrophone array with both horizontal and vertical apertures, also moored on the 120 m isobath. While the acoustics results are not explicitly discussed in this paper, the mooring locations are included to foster comparisons presented elsewhere [1], [2].…”

Section: A the Asiaex Programmentioning

confidence: 99%

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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344

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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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Section: A the Asiaex Programmentioning

confidence: 99%

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.

Self Cite

344

321

View full text Add to dashboard Cite

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“…Prior experiments have measured strong acoustic fluctuations after a few tens of kilometers of propagation through waters populated with waves of these types [8][9][10][11][12]. After such long propagation distances many intervening bathymetric, internal wave, and frontal features can cause multiple scattering effects.…”

Section: Introductionmentioning

confidence: 99%

Short-Range Acoustic Propagation Variability on a Shelf Area with Strong Nonlinear Internal Waves

Reeder

Duda

2008

OCEANS 2008 - MTS/IEEE Kobe Techno-Ocean

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-During April 2007 a six-day long experiment was conducted to measure internal waves and their acoustic effects at a continental shelf site in the Northern South China Sea. The site is slightly west of the edge of the shelf. At the shelf edge, large internal waves originating in the Luzon Strait area enter shallow water from deep water, undergoing rapid dissipation and wave shape evolution. A moored acoustic source transmitted 400-Hz pulses 3.0 and 6.0 km to two moored vertical line arrays, with geometry such that the propagation path was roughly parallel to the crests of the strongest passing internal waves, so that strong horizontal refraction effects are expected.Internal-wave characteristics and effects of the internal waves on the sound propagation, both observed and modeled, are shown here.

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“…Particular measured examples are the rapid swings in signal energy arriving at vertical line arrays over intervals of only a few minutes ͑Duda et Duda and Preisig, 1999;Lynch et al, 2003;Chiu et al, 2004͒. Here, by the term signal energy we mean depthintegrated intensity, which is used in other papers on this topic ͑Duda and Preisig, 1999;Oba and Finette, 2002͒. Many aspects of the fluctuations essentially validate that wave motion causes the fluctuations ͑i.e., that moving waves are responsible for fluctuations and that the scale S exists͒.…”

Section: Introductionmentioning

confidence: 99%

Temporal and cross-range coherence of sound traveling through shallow-water nonlinear internal wave packets

Duda

2006

The Journal of the Acoustical Society of America

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Expressions governing coherence scales of sound passing through a moving packet of nonlinear internal waves in a continental shelf environment are presented. The expressions describe the temporal coherence scale at a point, and the horizontal coherence scale in a plane transverse to the acoustic path, respectively. Factors in the expressions are the wave packet propagation speed, wave packet propagation direction, the fractional distance from the packet to the source, and the spatial scale S of packet displacement required to cause acoustic field decorrelation. The scale S is determined by the details of coupled mode propagation within the packet and the waveguide. Here, S is evaluated as a function of frequency for one environment, providing numerical values for the coherence scales of this environment. Coherence scales derived from numerical simulation of coupled mode acoustic propagation through moving wave packets substantiate the expressions.

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Acoustic Intensity Fluctuations Induced by South China Sea Internal Tides and Solitons

Cited by 62 publications

References 15 publications

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

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

Short-Range Acoustic Propagation Variability on a Shelf Area with Strong Nonlinear Internal Waves

Temporal and cross-range coherence of sound traveling through shallow-water nonlinear internal wave packets

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