Progress of regional oceanography study associated with western boundary current in the South China Sea

Abstract

Recent progress of physical oceanography in the South China Sea (SCS) associated with the western boundary current (WBC) and eddies is reviewed in this paper. It includes Argo observations of the WBC, eddy detection in the WBC based on satellite images, cross-continental shelf exchange in the WBC, eddy-current interaction, interannual variability of the WBC, air-sea interaction, the SCS throughflow (SCSTF), among others. The WBC in the SCS is strong, and its structure, variability and dynamic processes on seasonal and interannual time scales are yet to be fully understood. In this paper, we summarize progresses on the variability of the WBC, eddy-current interaction, air-sea interaction, and the SCSTF achieved in the past few years. Firstly, using the drifting buoy observations, we point out that the WBC becomes stronger and narrower after it reaches the central Vietnam coast. The possible mechanisms influencing the ocean circulation in the northern SCS are discussed, and the dynamic mechanisms that induce the countercurrent in the region of northern branch of WBC in winter are also studied quantitatively using momentum balance. The geostropic component of the WBC was diagnosed using the ship observation along 18°N, and we found that the WBC changed significantly on interannual time scale. Secondly, using the ship observations, two anti-cyclonic eddies in the winter of 2003/2004 in the northern SCS, and three anti-cyclonic eddies in the summer of 2007 along 18°N were studied. The results show that the two anti-cyclonic eddies can propagate southwestward along the continental shelf at the speed of first Rossby wave (~0.1 m s 1 ) in winter, and the interaction between the three anti-cyclonic eddies in summer and the WBC in the SCS is preliminarily revealed. Eddies on the continental shelf of northern SCS propagated southeastward with a maximum speed of 0.09 m s 1 , and those to the east of Vietnam coast had the largest kinetic energy, both of which imply strong interaction between eddy activity and WBC in the SCS. Thirdly, strong intraseasonal variability (ISV) of sea surface temperature (SST) near the WBC regions was found, and the ISV signal of SST in winter weakens the ISV signal of latent heat flux by 20%. Fourthly, the long-term change of SCSTF volume transport and its connection with the ocean circulation in the Pacific were discussed.South China Sea, western boundary current, eddy, eddy-current interaction, intraseasonal variability, South China Sea thoughflow Citation:Wang D X, Liu Q Y, Xie Q, et al. Progress of regional oceanography study associated with western boundary current in

Weakest winter South China Sea western boundary current caused by the 2015–2016 El Niño event

“…Like other western boundary currents, such as the Kuroshio Current [Stommel and Yoshida, 1972] or the Gulf Stream [Stommel, 1965] in the open ocean, the South China Sea western boundary current (SCSWBC) is also a swift and narrow jet. However, it reverses with the East Asian monsoon transition (i.e., poleward in summer and equatorward in winter) [Wang et al, 2013]. The SCSWBC serves as the main contributor to the redistribution of water properties, momentum, and energy in the SCS [Fang et al, 2012].…”

Ship observations and numerical simulation of the marine atmospheric boundary layer over the spring oceanic front in the northwestern South China Sea

“…The South China Sea (SCS) is a marginal sea linking the western Pacific Ocean and the eastern Indian Ocean (Figure 1a). The ocean circulation of the SCS is essentially cyclonic in winter and anticyclonic in summer, responding to the seasonally reversing monsoon [Wyrtki, 1961;Qu, 2000;Liu et al, 2001;Fang et al, 2005;Gan et al, 2006;Wang et al, 2013]. The interaction between the basin gyre, monsoon, bathymetry, and tide produces many ocean fronts that can be observed in the northern SCS throughout the year with apparent seasonal variation [Wang et al, 2001;Hu et al, 2003;Chu and Wang, 2003;Wang et al, 2012;Shi et al, 2014].…”

Low-Frequency Variability of Monsoon-Driven Circulation with Application to the South China Sea

“…Driven by monsoonal wind, the surface circulation in the SCS presents a basin-scale, cyclonic pattern in winter and a double-gyre structure in summer (Wyrtki 1961;Fang et al 1998;Hu et al 2000;Liu et al 2008;Wang et al 2013). Subsequent studies indicated that the seasonal variability of the SCS circulation is subjected to the quasisteady Sverdrup balance, after a fast adjustment associated with the first-order baroclinic Rossby waves (Liu et al 2001;Wang et al 2003). Besides seasonal variation, the upper-ocean circulation in the SCS varies on longer time scales as well.…”