Buoyancy Effect on the Winter South China Sea Western Boundary Current

The month‐to‐month variation of the winter South China Sea (SCS) western boundary current (WBC) along the western slope is examined using drifter observations, satellite altimetry data, and an ocean reanalysis. The most surprising phenomenon is that the WBC velocity at the sea surface reaches the ma...

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Bibliographic Details
Published in:Journal of geophysical research. Oceans 2019-10, Vol.124 (10), p.6871-6885
Main Authors: Yan, Yunwei, Wang, Guihua, Xue, Huijie, Chai, Fei
Format: Article
Language:English
Subjects:
Advection
Boundary currents
Buoyancy
buoyancy effect
Density
Density gradients
Geophysics
Intrusion
Pycnocline
Satellite altimetry
Satellite observation
Sea surface
Slopes
South China Sea
Surface velocity
Velocity
western boundary current
Wind
Wind effects
Winter
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Summary:The month‐to‐month variation of the winter South China Sea (SCS) western boundary current (WBC) along the western slope is examined using drifter observations, satellite altimetry data, and an ocean reanalysis. The most surprising phenomenon is that the WBC velocity at the sea surface reaches the maxima in November–December, which cannot be explained by wind forcing and Kuroshio intrusion alone. Analysis results demonstrate that buoyancy effect should be considered to explain the month‐to‐month variation besides wind‐Kuroshio effects. In winter, cold‐and‐salty advection by the WBC from the north decreases/reverses the zonal density gradient in the seasonal pycnocline induced by wind forcing and Kuroshio intrusion and therefore weakens wind‐Kuroshio‐induced WBC. Buoyancy effect on the winter SCS WBC is opposite to wind‐Kuroshio effects. In addition, buoyancy effect reaches the maximum in January, which is concurrent with wind‐Kuroshio effects. As a result of their competition, the zonal density gradient in the seasonal pycnocline is maximum in November–December, resulting in the maximum surface velocity along the western slope occurring in November‐December. This study demonstrates the importance of buoyancy forcing to the winter SCS WBC. Key Points Surface velocity of western boundary current reaches the maxima in November–December, which cannot be explained by wind‐Kuroshio alone Buoyancy weakens western boundary current by decreasing the zonal density gradient in the pycnocline, which is opposite to wind‐Kuroshio As a result of the competition, the zonal density gradient in the pycnocline is maximum in November–December, causing the maximum velocity
ISSN:2169-9275
2169-9291
DOI:10.1029/2019JC015079