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General Session 1: Physical oceanic processes: Dynamics and physical-biological-biogeochemical interactions |
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Formation and dynamics of a long-lived eddy-train in the South China Sea
Tuesday 10th @ 1130-1145
Multi-function Hall
Zhongya Cai* , Hong Kong University of Science and Technology
Jianping Gan, Hong Kong University of Science and Technology
Presenter Email: zcaiaa@connect.ust.hk
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| Observations showed that long-lived anticyclonic eddies (AEs) formed an eddy-train along wind-induced jet current across the northern South China Sea (NSCS) basin in summer. The eddy-train plays a critical role in regulating ocean circulation in the NSCS, yet its formation dynamics remain unclear. We conducted a modeling study to investigate the formation process and underlying forcing mechanism of the eddy-train. Forced by prevailing southwesterly monsoon wind, the northward coastal jet separates from the west boundary of the South China Sea (SCS) basin and overshoots northeastward. The development of the anticyclonic recirculation along the separated jet strengthens the jet and its negative shear vorticity, which meanders the jet and forms the AEs sequentially, or an eddy-train along the jet. The anticyclonic recirculation of the separated jet forms the first AE. The jet meanders downstream with its strong negative shear vorticity and forms the second and the third AEs along the jet sequentially, or an eddy-train. Vertically, AEs weaken gradually from the surface to the depth ocean. The inherent stratification in the SCS regulates the three-dimensional spatial scale of the AEs and has negative effects on the vertical extension of AEs. Analyses of vorticity balance equation indicate that negative vorticity of the eddy-train originates from the beta effect of the northward western boundary current, which is subsequently advected downstream by the separated jet and forms the AEs. The jet separation is a necessary condition for the formation of eddy-train, and the enhanced stratification, increased wind stress and wind stress curl are favorable conditions for AEs formation. |
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