Effects of a subsurface abnormal anticyclonic eddy on sound propagation in the northwest continental slope of the South China Sea

Zeng Feihong; Xie Lingling; Wu Kaiming; Li Qiang; Li Mingming; Liu Simeng

doi:10.12284/hyxb2024083

Volume 46 Issue 8

Sep. 2024

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Zeng Feihong，Xie Lingling，Wu Kaiming, et al. Effects of a subsurface abnormal anticyclonic eddy on sound propagation in the northwest continental slope of the South China Sea[J]. Haiyang Xuebao，2024, 46(8)：19–36 doi: 10.12284/hyxb2024083

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Effects of a subsurface abnormal anticyclonic eddy on sound propagation in the northwest continental slope of the South China Sea

doi: 10.12284/hyxb2024083

Zeng Feihong^1
,,
Xie Lingling^{1, 2, 3
,
,},
Wu Kaiming⁴,
Li Qiang^{1, 2, 3},
Li Mingming^{1, 2, 3},
Liu Simeng¹

1.
Laboratory of Coastal Ocean Variation and Disaster Prediction, College of Oceanology and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
2.
Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Ocean, Zhanjiang 524088, China
3.
Key Laboratory of Space Ocean Remote Sensing and Application, Ministry of Natural Resources, Zhanjiang 524088, China
4.
National Key Laboratory of Science and Technology on Underwater Acoustic Antagonizing, Zhanjiang 524022, China

Received Date: 2024-03-07
Rev Recd Date: 2024-06-26

Available Online: 2024-08-16

Publish Date: 2024-09-26

Abstract

Abstract

Using temperature-salinity profiles and current measurements, satellite data and reanalysis data in April 2018, this study analyses the acoustic field characteristics and effects of an abnormal anticyclonic eddy (AAE) on acoustic propagation on the continental slope area in the northwestern South China Sea (SCS). The results show that the AAE has a lens-shaped structure with a surface cold core, a shallower mixed layer, and subsurface intensified velocities. Unlike the concave sound-speed contours in the normal anticyclonic eddy (NAE), the sound-speed distribution in the abnormal anticyclonic eddy (AAE) exhibits a lens-shaped structure with an upward convexity and downward concavity. The surface sound speed within the eddy is lower than that outside, showing a negative anomaly (<−2 m/s). Conversely, the sound speed in the subsurface layer of the eddy is higher than that outside, showing a positive anomaly (>11 m/s). This results in the thickness of the original double thermocline extending up and down by a total of 47 meters in the presence of the eddy. As the sound propagates from the eddy outside on the shelf to the deep sea, the surface sound channel disappears as the propagation distances decreasing in the AAE, contrast to the increased distance in the NAE. As the sound propagates from the eddy outside in the deep ocean to the shelf, the location of the sound energy convergence zone moves backward and downward in the AAE, with the maximum distance exceeding 24 km and 0.3 km, respectively. This is similar to the situation in the NAE. As the sound propagates from the eddy core to outside in the deep sea, the turning depth of the sound deepens and the distance between the sound energy convergence zones doubles in the AAE, while no changes in the NAE.
- abnormal anticyclonic eddy,
- underwater sound propagation,
- convergence zone,
- northwest continental slope of the South China Sea

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References(45)

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