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Dynamics of the Cross-Layer Exchange for the Layered Circulation in the South China Sea
Cai, Zhongya1,2; Gan, Jianping1
Source PublicationJournal of Geophysical Research- Oceans

The cyclonic-anticyclonic-cyclonic (CAC) circulation in the upper (<750 m)-middle (750–1,500 m)-deep (>1,500 m) layers of South China Sea (SCS) is mainly driven by the extrinsic lateral vorticity flux due to inflow-outflow-inflow through the Luzon Strait (LS) and the associated intrinsic vertical exchange (VE) in the basin. The contribution of spatiotemporal structure of the VE through vortex stretching and squeezing to CAC circulation, which was unknown, mainly occurs in the semi-closed middle and deep layers and has a strong seasonality. During summer, the vorticity flux induced by net upward VEs crossing the upper (750 m) and lower (1,500 m) interfaces of CAC circulation is equivalent to ~40% of the lateral vorticity flux for strengthening the anticyclonic and cyclonic circulation in the middle and deep layers, respectively. During winter, the net downward VE crossing the upper interface squeezes the middle layer and strengthens its anticyclonic circulation, while the net VE crossing the lower interface is too small to affect the circulation. The VE and its seasonality in the basin are largely governed by the cross-isobath geostrophic transport (CGT) due to interaction between along-isobath circular currents and rugged slope topography. The CGT is formed by the along-isobath bottom pressure gradient associated with surface wind stress curl, nonlinear advection, and beta effect over the meandering slope topography. Our study revealed how important VE between the layers is to the CAC circulation itself, and our work advanced the understanding of the intrinsic-extrinsic dynamic coupling that forms, develops, and sustains the CAC circulation in the SCS.

KeywordExternal Forcing Internal Dynamics Layered Circulation South China Sea Vertical Exchange Vortex Stretching And Squeezing
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Indexed BySCIE
WOS Research AreaOceanography
WOS SubjectOceanography
WOS IDWOS:000577126400025
Scopus ID2-s2.0-85089894470
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Document TypeJournal article
Corresponding AuthorGan, Jianping
Affiliation1.Department of Ocean Science and Department of Mathematics, The Hong Kong University of Science and Technology, Hong Kong
2.State Key Laboratory of Internet of Things for Smart City and Department of Civil and Environmental Engineering, University of Macau, Macao
First Author AffilicationUniversity of Macau
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GB/T 7714
Cai, Zhongya,Gan, Jianping. Dynamics of the Cross-Layer Exchange for the Layered Circulation in the South China Sea[J]. Journal of Geophysical Research- Oceans,2020,125(8):e2020JC016131.
APA Cai, Zhongya,&Gan, Jianping.(2020).Dynamics of the Cross-Layer Exchange for the Layered Circulation in the South China Sea.Journal of Geophysical Research- Oceans,125(8),e2020JC016131.
MLA Cai, Zhongya,et al."Dynamics of the Cross-Layer Exchange for the Layered Circulation in the South China Sea".Journal of Geophysical Research- Oceans 125.8(2020):e2020JC016131.
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