Energetic Topographic Rossby Waves in the Northern South China Sea

Qiang Wang State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Lili Zeng State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Yeqiang Shu State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Jian Li State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Ju Chen State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Yunkai He State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Jinglong Yao State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Dongxiao Wang State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Weidong Zhou State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

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Abstract

Topographic Rossby waves (TRWs) are reported to make a significant contribution to the deep-ocean current variability. On the northern South China Sea (NSCS) continental slope, TRWs with peak spectral energy at ~14.5 days are observed over about a year at deep moorings aligned east–west around the Dongsha Islands. The TRWs with a group velocity of O(10) cm s−1 contribute more than 40% of total bottom velocity fluctuations at the two mooring stations. The energy propagation and source are further identified using a ray-tracing model. The TRW energy mainly propagates westward along the NSCS continental slope with a slight downslope component. The possible energy source is upper-ocean 10–20-day fluctuations on the east side of the Dongsha Islands, which are transferred through the first baroclinic mode (i.e., the second EOF mode). These 10–20-day fluctuations in the upper ocean are associated with mesoscale eddies. However, to the west of the Dongsha Islands, the 10–20-day fluctuations in the upper ocean are too weak to effectively generate TRWs locally. This work provides an interesting insight toward understanding the NSCS deep current variability and the linkage between the upper- and deep-ocean currents.

© 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Dongxiao Wang, dxwang@scsio.ac.cn

Abstract

Topographic Rossby waves (TRWs) are reported to make a significant contribution to the deep-ocean current variability. On the northern South China Sea (NSCS) continental slope, TRWs with peak spectral energy at ~14.5 days are observed over about a year at deep moorings aligned east–west around the Dongsha Islands. The TRWs with a group velocity of O(10) cm s−1 contribute more than 40% of total bottom velocity fluctuations at the two mooring stations. The energy propagation and source are further identified using a ray-tracing model. The TRW energy mainly propagates westward along the NSCS continental slope with a slight downslope component. The possible energy source is upper-ocean 10–20-day fluctuations on the east side of the Dongsha Islands, which are transferred through the first baroclinic mode (i.e., the second EOF mode). These 10–20-day fluctuations in the upper ocean are associated with mesoscale eddies. However, to the west of the Dongsha Islands, the 10–20-day fluctuations in the upper ocean are too weak to effectively generate TRWs locally. This work provides an interesting insight toward understanding the NSCS deep current variability and the linkage between the upper- and deep-ocean currents.

© 2019 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Dongxiao Wang, dxwang@scsio.ac.cn
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