Warm water wake off northeast Vietnam in the South China Sea
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Warm water wake off northeast Vietnam in the South China Sea YAN Yunwei1,2, CHEN Changlin2*, LING Zheng2 1 2
College of Physical and Environmental Oceanography, Ocean University of China, Qingdao 266100, China State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
Received 24 February 2014; accepted 13 June 2014 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract Due to orographic blockage, a weak wind wake occurs in summer off northeast Vietnam in the South China Sea. Under the wind wake, warm water is observed from both high-resolution satellite data and hydrographic observations. The wake of warm water forms in June, continues to mature in July and August, starts to decay in September, and disappears in October. The warm water wake also shows robust diurnal variation – it intensifies during the day and weakens in the night. Warm water wakes can be generated through wind-induced mixing and thermal (latent heat flux) processes. In this paper, a mixed layer model is used to evaluate the relative importance of the two processes on seasonal and diurnal timescales, respectively. The results demonstrate that thermal processes make a greater contribution to the wake than wind-induced mixing processes on a seasonal timescale, while the warm water wake is dominated by wind-induced mixing processes on a diurnal timescale. Key words: warm water wake, wind-induced mixing processes, thermal processes, seasonal timescale, diurnal timescale, northeast Vietnam, South China Sea Citation: Yan Yunwei, Chen Changlin, Ling Zheng. 2014. Warm water wake off northeast Vietnam in the South China Sea. Acta Oceanologica Sinica, 33(11): 55–63, doi: 10.1007/s13131-014-0555-x
1 Introduction The South China Sea (SCS) is the largest marginal sea in Southeast Asia surrounded by the Indo-China Peninsula to the west and South China to the north (Fig. 1a). On the east coast of Indo-China Peninsula, mountain ranges, named Annam Cordillera, lie in the north-south direction and can be divided into three segments (north, middle, and south segments) according to the land topography with elevations greater than 800 m. Ngoc Linh, the highest mount in the middle segment, is a 2 598 m high mountain. Under the control of the East Asian monsoon, the SCS is dominated by the southwest monsoon in summer (Wyrtki, 1961; Qu, 2000; Liu et al., 2001). In this study, summer refers to June, July, and August. As the southwest summer monsoon impinges on Annam Cordillera, a strong wind jet forms at the southern tip of the mountains (Xie et al., 2003). Beyond that, we also notice that a weak wind wake appears in the lee of the middle segment of Annam Cordillera off northeast Vietnam (Fig. 1a). Sea surface temperature (SST) in the SCS has been widely documented in previous studies (e.g., Qu, 2001; Wang et al., 2002; Xie et al., 2003; Liu et al, 2004; Wang et al., 2006). In summer, Xie et al. (2003) found that the cold water along the south Vi
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