An exceptional anticyclonic eddy in the South China Sea in 2010

Abstract

The highest sea level near the Xisha Islands in recent 20 years occurred during August 2010.Satellite altimeter data indicated that the extreme event was largely due to an anticyclonic eddy, whose amplitude exceeded 20 cm and size exceeded 400 km on 11 August 2010. Cruise observations showed the eddy raised the center temperature by 7.7 C at 75 m and vertically extended to 500 m. Eddy tracking showed it had a life span of more than 8 months and propagated far from the south of Xisha Islands. Such strong and long-lasting eddy that moved northward for such a long distance was observed for the first time in the South China Sea (SCS). Observational data from CTD/XBT and the reconstructed three-dimensional temperature and salinity were used to explore the eddy's features and vertical structure. Our analyses show the 2010 summer monsoon and current in the western boundary of the SCS were largely altered after the 09/10 El Niño event. From May onward, the wind blew northward and strengthened over the northwestern SCS. Such wind drove a strong northward current along the western boundary, which carried the eddy northward by advection from May to July. Energy budget showed, during the eddy northward propagation, the boundary current passed energy to the eddy, which led to the continuing growth of the eddy in both strength and size.

Evaluation of Satellite-Altimetry-Derived Pycnocline Depth Products in the South China Sea

“…However, both the altimeter-derived products underestimate the cruise-data-derived ULT off the southeast coast of Vietnam in August 2000 (second column in Figure 9). That may be because of the effects of an anticyclonic eddy, which is part of a dipole eddy pair associated with the summer eastward jet (e.g., [14,26,27,31,32]). The details still need further study.…”

Toward a Mesoscale Hydrological and Marine Meteorological Observation Network in the South China Sea

“…High mesoscale eddy activity and unique regional air-sea coupling patterns have been observed in the SCS (Dale 1956;Qu 2000;Chu and Fan 2001;Yuan et al 2007;Chen et al 2009Chen et al , 2011He et al 2013;Chu et al 2014). The geographic distribution of eddy energy shows that the higher eddy kinetic energies are located to the east of Vietnam and to the west of Taiwan (Chen et al 2009;Cheng and Qi 2010).…”

“…In 2010, an extremely large and long-lasting warm eddy was observed in the SCS to be moving northward from the south of the Xisha Islands. The CTD and expendable bathythermographs measurements obtained during the 2010 warm eddy cruise were used to explore the eddy's vertical structure (Chu et al 2014). A seasonal eddy dipole pattern usually exists off the Vietnam coast from summer to fall, with a cyclonic eddy in the north and an anticyclonic eddy in the south (G. G.…”

“…Chen et al 2010). During an El Niño year, this dipole pattern weakens or even disappears because of the weaker summer monsoon wind (e.g., G. Yang et al 2007;Du et al 2009;Xie et al 2009), which could lead to an enhanced warm eddy in the northwestern SCS (e.g., Chu et al 2014). The heat advected by eddies can have a marked effect on the spatial distribution of sea surface temperature (SST) in the SCS, which results in an uneven surface wind field that is faster (slower) over the warm (cold) tongues than the surrounding area (Chow and Liu 2012).…”

Interannual variability of the eastward current in the western South China Sea associated with the summer Asian monsoon

“…For the northward shift type, the composited years include 1995, 1998, 2006, 2007, and 2008, when Y E was among the five largest [the year of 2010 is excluded because the eastward current shifted to a very north location, and an exceptionally strong anticyclonic eddy appeared between 12 N and 18 N; Chu et al, 2014]. For the southward shift type, the composite is based on the years of 1994, 1997, Figure 5 shows the climatology of summermean SLA and the composited SLA maps for the two different types.…”