Seasonal variability of the isopycnal surface circulation in the South China Sea derived from a variable-grid global oce
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Seasonal variability of the isopycnal surface circulation in the South China Sea derived from a variable-grid global ocean circulation model WEI Zexun1, 2, 3*, FANG Guohong1, 2, 3, XU Tengfei1, 2, 3, WANG Yonggang1, 2, 3, LIAN Zhan1, 2, 3 1 First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China 2 Laboratory for Regional Oceanography and Numerical Modeling, Qingdao National Laboratory for Marine Science
and Technology, Qingdao 266061, China 3 Key Lab of Marine Science and Numerical Modeling, State Oceanic Administration, Qingdao 266061, China
Received 19 March 2015; accepted 8 September 2015 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2016
Abstract
In this study, we develop a variable-grid global ocean general circulation model (OGCM) with a fine grid (1/6)° covering the area from 20°S–50°N and from 99°–150°E, and use the model to investigate the isopycnal surface circulation in the South China Sea (SCS). The simulated results show four layer structures in vertical: the surface and subsurface circulation of the SCS are characterized by the monsoon driven circulation, with basin-scaled cyclonic gyre in winter and anti-cyclonic gyre in summer. The intermediate layer circulation is opposite to the upper layer, showing anti-cyclonic gyre in winter but cyclonic gyre in summer. The circulation in the deep layer is much weaker in spring and summer, with the maximum velocity speed below 0.6 cm/s. In fall and winter, the SCS deep layer circulation shows strong east boundary current along the west coast of Philippine with the velocity speed at 1.5 m/s, which flows southward in fall and northward in winter. The results have also revealed a fourlayer vertical structure of water exchange through the Luzon Strait. The dynamics of the intermediate and deep circulation are attributed to the monsoon driving and the Luzon Strait transport forcing. Key words: South China Sea, isopycnal surface circulation, ocean general circulation model, Luzon Strait transport Citation: Wei Zexun, Fang Guohong, Xu Tengfei, Wang Yonggang, Lian Zhan. 2016. Seasonal variability of the isopycnal surface circulation in the South China Sea derived from a variable-grid global ocean circulation model. Acta Oceanologica Sinica, 35(1): 11–20, doi: 10.1007/s13131-016-0791-3
1 Introduction The South China Sea (SCS), with an area of about 3.5 million km2, is the largest semi-enclosed marginal sea in the Northwest Pacific Ocean (Fig. 1). The SCS circulation plays an important role in the inter-ocean circulation between the Pacific and Indian Oceans (Fang et al., 2003, 2005, 2009, 2010; Gordon et al., 2012), refers to as the South China Sea Throughflow (Qu et al., 2005; Qu et al., 2006a; Yu et al., 2007; Yaremchuk et al., 2009; Qu et al., 2009). The upper layer circulation in the South China Sea has been documented by previous studies (Wyrtki, 1961; Metzger and Hurlburt, 1996; Fang et al., 1998; Wu et al., 1998; Chu et al., 1999; Ho et al., 2000; Qu, 2000; Hu et al., 2000; Fang et al., 2002a; Xue et a
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