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    Shelf-edge frontal structure in the central East China Sea and its impact on low-frequency acoustic propagation

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    IEEEjoe102004ECSfrontal.pdf (4.260Mb)
    Date
    2004-10
    Author
    Ramp, Steven R.  Concept link
    Chiu, Ching-Sang  Concept link
    Bahr, Frederick L.  Concept link
    Qi, Yiquan  Concept link
    Dahl, Peter H.  Concept link
    Miller, James H.  Concept link
    Lynch, James F.  Concept link
    Zhang, Renhe  Concept link
    Zhou, Ji-Xun  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/673
    As published
    https://doi.org/10.1109/JOE.2004.840842
    DOI
    10.1109/JOE.2004.840842
    Keyword
     Environmental acoustics; Internal waves; Kuroshio Current; Shelf circulation 
    Abstract
    Two field programs, both parts of the Asian Seas International Acoustics Experiment (ASIAEX), were carried out in the central East China Sea (28 to 30 N, 126 30 to 128 E) during April 2000 and June 2001. The goal of these programs was to study the interactions between the shelf edge environment and acoustic propagation at a wide range of frequencies and spatial scales. The low-frequency across-slope propagation was studied using a synthesis of data collected during both years including conductivity- temperature-depth (CTD) and mooring data from 2000, and XBT, thermistor chain, and wide-band source data from 2001. The water column variability during both years was dominated by the Kuroshio Current flowing from southwest to northeast over the continental slope. The barotropic tide was a mixed diurnal/semidiurnal tide with moderate amplitude compared to other parts of the Yellow and East China Sea. A large amplitude semidiurnal internal tide was also a prominent feature of the data during both years. Bursts of high-frequency internal waves were often observed, but these took the form of internal solitons only once, when a rapid off-shelf excursion of the Kuroshio coincided with the ebbing tide. Two case studies in the acoustic transmission loss (TL) over the continental shelf and slope were performed. First, anchor station data obtained during 2000 were used to study how a Kuroshio warm filament on the shelf induced variance in the transmission loss (TL) along the seafloor in the NW quadrant of the study region. The corresponding modeled single-frequency TL structure explained the significant fine-scale variability in time primarily by the changes in the multipath/multimode interference pattern. The interference was quite sensitive to small changes in the phase differences between individual paths/modes induced by the evolution of the warm filament. Second, the across-slope sound speed sections from 2001 were used to explain the observed phenomenon of abrupt signal attenuation as the transmission range lengthened seaward across the continental shelf and slope. This abrupt signal degradation was caused by the Kuroshio frontal gradients that produced an increasingly downward-refracting sound-speed field seaward from the shelf break. This abrupt signal dropout was explained using normal mode theory and was predictable and source depth dependent. For a source located above the turning depth of the highest-order shelf-trapped mode, none of the propagating modes on the shelf were excited, causing total signal extinction on the shelf.
    Description
    Author Posting. © IEEE, 2004. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 29 (2004): 1011-1031, doi:10.1109/JOE.2004.840842.
    Collections
    • Applied Ocean Physics and Engineering (AOP&E)
    Suggested Citation
    IEEE Journal of Oceanic Engineering 29 (2004): 1011-1031
     

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