On the mechanism of the cyclonic circulation in the Gulf of Tonkin in the summer
On the mechanism of the cyclonic circulation in the Gulf of Tonkin in the summer
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DOI：
10.1029/2007jc004208
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发表时间：
2008-09
影响因子：
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通讯作者：
Dexing Wu;Yue Wang;Xiaopei Lin;Jiayan Yang
中科院分区：
文献类型：
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作者：
Dexing Wu;Yue Wang;Xiaopei Lin;Jiayan Yang
[1]传统上认为东京湾的环流在夏季是反气旋的。这一观点最近受到重新分析观测数据的结果的挑战，这些结果清楚地表明，环流在所有季节都是气旋性的。地面风应力是季风性的，夏季为西南风，冬季为反向风。目前仍无法解释为什么环流总是气旋式的，而地面强迫季节性地反转。在本研究中，我们假设琼州海峡是海南岛与中国大陆之间的一个浅而狭窄的通道，通过琼州海峡的流入负责维持夏季的气旋环流。除了质量守恒和测深约束的要求外，这种流动即使具有相当小的输运量，也会携带相当数量的位涡量（PV）进入海湾，而PV的积分约束要求存在摩擦扭矩才能与气旋环流相关联。为了验证这一假设，已经进行了几个三维模型的数值实验。当通过琼州海峡的西向气流受阻时，模式模拟夏季的反气旋环流。当允许向西气流通过琼州海峡时，环流转变为气旋型，符合我们的假设。
[1] The circulation in the Gulf of Tonkin had been traditionally considered to be anticyclonic in the summer. This view was challenged recently by results from reanalyzing observational data, which clearly revealed that the circulation is cyclonic in all seasons. The surface wind stress is monsoonal, southwesterly in the summer and reversed in the winter. It remains unexplained why the circulation is always cyclonic, while the surface forcing reverses seasonally. In this study, we hypothesize that the inflow through Qiongzhou Strait, a shallow and narrow channel between Hainan Island and the Chinese mainland, is responsible for maintaining the cyclonic circulation in the summer. Besides the requirements of mass conservation and bathymetry constraint, this flow, even with a rather small transport, carries a considerable amount of potential vorticity (PV) into the gulf, and the integral constraint of PV requires the presence of a frictional torque to be associated with a cyclonic circulation. Several numerical experiments with a three-dimensional model have been conducted to test this hypothesis. When the westward flow through Qiongzhou Strait is blocked, the model simulates an anticyclonic circulation in the summer. When the westward flow through Qiongzhou Strait is allowed, the circulation changes to a cyclonic one, consistent with our hypothesis.