Kuroshio intrusion into the South China Sea with an anticyclonic eddy: evidence from underwater glider observation

AbstractA process-oriented numerical modeling study was conducted to investigate the formation and underlying forcing of an anticyclonic eddy train observed in the northern South China Sea. Observations showed that long-lived anticyclonic eddies formed an eddy train along an eastward separated jet across the northern South China Sea in summer. The eddy train plays a critical role in regulating ocean circulation in the region. Forced by the southwesterly monsoon and prevailing dipole wind stress curl in the summer, the northward coastal jet separates from the west boundary of the South China Sea basin and overshoots northeastward into the basin. The anticyclonic recirculation of the separated jet forms the first anticyclonic eddy in the eddy train. The jet meanders downstream with a strong negative shear vorticity that forms a second and a third anticyclonic eddy along the jet’s path. These three eddies form the eddy train. These eddies weaken gradually with depth from surface, but they can extend to approximately 500 m deep. The inherent stratification in the region regulates the three-dimensional scale of the anticyclonic eddies and constrains their intensity vertical extension by weakening the geostrophic balance within these eddies. Analyses of the vorticity balance indicate that the eddy train’s negative vorticity originates from the beta effect of northward western boundary current and from the subsequent downstream vorticity advection in the jet. The jet separation is a necessary condition for the formation of the eddy train, and the enhanced stratification, increased summer wind stress, and associated negative wind stress curl are favorable conditions for the formation of the anticyclonic eddies.

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Optimal Precursors Triggering the Kuroshio Intrusion Into the South China Sea Obtained by the Conditional Nonlinear Optimal Perturbation Approach

Journal of Geophysical Research Oceans ◽

10.1029/2018jc014545 ◽

2019 ◽

Vol 124 (6) ◽

pp. 3941-3962 ◽

Cited By ~ 1

Author(s):

Peng Liang ◽

Mu Mu ◽

Qiang Wang ◽

Lina Yang

Keyword(s):

South China Sea ◽

South China ◽

The South China Sea ◽

Perturbation Approach ◽

Kuroshio Intrusion ◽

The South ◽

Conditional Nonlinear Optimal Perturbation ◽

Optimal Perturbation ◽

China Sea ◽

The Kuroshio

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Weakening of the Kuroshio Intrusion into the South China Sea over the Past Two Decades

Journal of Climate ◽

10.1175/jcli-d-12-00315.1 ◽

2013 ◽

Vol 26 (20) ◽

pp. 8097-8110 ◽

Cited By ~ 39

Author(s):

Feng Nan ◽

Huijie Xue ◽

Fei Chai ◽

Dongxiao Wang ◽

Fei Yu ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Luzon Strait ◽

The South China Sea ◽

Negative Trend ◽

Kuroshio Intrusion ◽

The South ◽

China Sea ◽

The Past ◽

The Kuroshio

Abstract Inferred from the satellite and in situ hydrographic data from the 1990s and 2000s, the Kuroshio intrusion into the South China Sea (SCS) had a weakening trend over the past two decades. Associated with the weakened Kuroshio intrusion, the Kuroshio loop and eddy activity southwest of Taiwan became weaker, whereas the water above the salinity minimum became less saline in the northern SCS. The sea surface height southwest of Taiwan increased at a slower rate compared to other regions of the SCS because of the weakened Kuroshio intrusion. Simulations using the Regional Ocean Modeling System (ROMS) Pacific model show that the strength of the Kuroshio intrusion into the SCS decreased from 1993 to 2010 with a negative trend, −0.24 sverdrups (Sv) yr−1 (1 Sv ≡ 106 m3 s−1), in the total Luzon Strait transport (LST). Although wind-induced Ekman transport through the Luzon Strait became weaker, the magnitude at 0.001 Sv yr−1 was too small to compensate for the negative trend of the LST. On the other hand, the piling up of the water induced by monsoon winds was an important mechanism for changing the pressure gradient across the Luzon Strait and eventually affecting the LST. The sea level gradient between the western Pacific and the SCS had a negative trend, −0.10 cm yr−1, corresponding to a negative trend in the geostrophic transport at −0.20 Sv yr−1. The Kuroshio transport east of Luzon Island also had a negative trend, which might also be linked to the weakening Kuroshio intrusion.

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