Qu Tangdong

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Qu
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Tangdong
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  • Article
    Deep South China Sea circulation
    (American Geophysical Union, 2011-03-01) Wang, Guihua ; Xie, Shang-Ping ; Qu, Tangdong ; Huang, Rui Xin
    The analysis of an updated monthly climatology of observed temperature and salinity from the U.S. Navy Generalized Digital Environment Model reveals a basin-scale cyclonic circulation over the deep South China Sea (SCS). The cyclonic circulation lies from about 2400 m to the bottom. The boundary current transport of the cyclonic circulation is around 3.0 Sv. Our results suggest that the cyclonic circulation is mainly forced by the Luzon overflow, with bottom topography playing an important role. The structures of potential temperature, salinity, and potential density in the deep SCS are consistent with the existence of the cyclonic circulation. Specifically, low salinity water is found in the interior region west of Luzon Island, and surrounded by saline Pacific water in boundary current regions to the north, west and southwest. Our results show the potential density distribution and the corresponding cyclonic circulation in deep SCS are primarily controlled by salinity variations in the deep basin.
  • Article
    Deepwater overflow through Luzon Strait
    (American Geophysical Union, 2006-01-10) Qu, Tangdong ; Girton, James B. ; Whitehead, John A.
    This study examines water property distributions in the deep South China Sea and adjoining Pacific Ocean using all available hydrographic data. Our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the Pacific into the South China Sea through Luzon Strait. Applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the Luzon Strait yields a transport estimate of 2.5 Sv (1 Sv=106 m3 s-1). Some implications of this result include: (i) a residence time of less than 30 years in the deep South China Sea, (ii) a mean diapycnal diffusivity as large as 10-3 m2 s-1, and (iii) an abyssal upwelling rate of about 3×10-6 m s-1. These quantities are consistent with residence times based on oxygen consumption rates. The fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the North Pacific. Density distributions within the South China Sea basin suggest a cyclonic deep boundary current system, as might be expected for an overflow-driven abyssal circulation.
  • Article
    Interannual variability of the South China Sea throughflow inferred from wind data and an ocean data assimilation product
    (American Geophysical Union, 2006-07-26) Wang, Dong Xiao ; Liu, Qinyan ; Huang, Rui Xin ; Du, Yan ; Qu, Tangdong
    The Luzon Strait transport, as an index for the South China Sea throughflow, has attracted much attention. In this study the interannual variability of the Luzon Strait transport is examined, using the Island Rule and results from an ocean general circulation model. Transport variability obtained from these two approaches are consistent with each other. Assessment of contribution from each integral segment involved in the Island Rule indicates that wind stress in the western and central equatorial Pacific is the key factor regulating the interannual variability of the Luzon Strait transport, whereas the effect of local wind stress in the vicinity of the Luzon Strait is secondary. Analysis also shows that when the westerly (easterly) wind anomalies in the tropical Pacific break out, the Luzon Strait transport increases (decreases), consistent with the variations in the North Equatorial Current during El Niño (La Niña) events.