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ZHANG Cong, DING Yang, BAO Xianwen, BI Congcong, LI Ruixiang, ZHANG Cunjie, SHEN Biao, WAN Kai. A numerical study of the South China Sea Warm Current during winter monsoon relaxation[J]. HaiyangYuHuZhao, 2018, 36(2): 216-229

A numerical study of the South China Sea Warm Current during winter monsoon relaxation

ZHANG Cong1,2, DING Yang2, BAO Xianwen1,2, BI Congcong1,2, LI Ruixiang3, ZHANG Cunjie1,2, SHEN Biao2, WAN Kai4
1 College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China;
2 Key Laboratory of Physical Oceanography, Ministry of Education, Ocean University of China, Qingdao 266100, China;
3 South China Sea Marine Survey and Technology Center, State Ocean Administration, Guangzhou 510310, China;
4 Beihai Offshore Engineering Survey Institute, State Oceanic Administration, Qingdao 266061, China
Using a Finite-Volume Community Ocean Model, we investigated the dynamic mechanism of the South China Sea Warm Current (SCSWC) in the northern South China Sea (NSCS) during winter monsoon relaxation. The model reproduces the mean surface circulation of the NSCS during winter, while model-simulated subtidal currents generally capture its current pattern. The model shows that the current over the continental shelf is generally southwestward, under a strong winter monsoon condition, but a northeastward counter-wind current usually develops between 50-and 100-m isobaths, when the monsoon relaxes. Model experiments, focusing on the wind relaxation process, show that sea level is elevated in the northwestern South China Sea (SCS), related to the persistent northeasterly monsoon. Following wind relaxation, a high sea level band builds up along the mid-shelf, and a northeastward current develops, having an obvious vertical barotropic structure. Momentum balance analysis indicates that an along-shelf pressure gradient provides the initial driving force for the SCSWC during the first few days following wind relaxation. The SCSWC subsequently reaches a steady quasi-geostrophic balance in the cross-shelf direction, mainly linked to sea level adjustment over the shelf. Lagrangian particle tracking experiments show that both the southwestward coastal current and slope current contribute to the northeastward movement of the SCSWC during winter monsoon relaxation.
Key words:    northern South China Sea|South China Sea Warm Current|monsoon relaxation|numerical model|pressure gradient|barotropic structure   
Received: 2016-11-17   Revised:
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