The bimodality of the Luzon Strait deep water
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摘要: Combined conductivity-temperature-depth (CTD) casts and Argo profiles, 3 086 historical hydrocasts were used to quantify the water column characteristics in the northern South China Sea (SCS) and its adjacent waters. Based on a two-dimensional "gravest empirical mode" (GEM), a gravitational potential (φ, a vertically integrated variable) was used as proxy for the vertical temperature profiles TG(p, φ).φ integrated from 8 MPa to the surface shows a close relationship with the temperature, except in the deep layer greater than 15 MPa, which was caused by the bimodal deep water in the region. The GEM temperature profiles successfully revealed the bimodality of the Luzon Strait deep water, that disparate hydrophic vertical profiles can produce distinct specific volume anomaly (δ) in the SCS and the western Philippine Sea (WPS), but failed in the Luzon Strait, where different temperature profiles may produce a same δ. A significant temperature divergence between the SCS water and the WPS water confirmed that the bimodal structure is strong. The deepwater bifurcation starts at about 15 MPa, and gets stronger with increasing depth . As the only deep channel connecting the bimodal-structure waters, water column characteristics in the Luzon Strait is in between, but much closer to the SCS water because of its better connectivity with the SCS. A bimodal temperature structure below 15 MPa reveals that there was a persistent baroclinic pressure gradient driving flow through the Luzon Strait. A volume flux predicted through the Bashi Channel with the hydraulic theory yields a value of 5.62×106 m3/s using all available profiles upstream and downstream of the overflow region, and 4.03×106 and 2.70×106 m3/s by exclusively using the profiles collected during spring and summer, respectively. No volume flux was calculated during autumn and winter because profiles are only available for the upstream of the Bashi Channel during the corresponding period.
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关键词:
- LuzonStrait /
- historicalhydrocasts /
- gravestempiricalmode /
- deepwater /
- bimodality /
- volumeflux
Abstract: Combined conductivity-temperature-depth (CTD) casts and Argo profiles, 3 086 historical hydrocasts were used to quantify the water column characteristics in the northern South China Sea (SCS) and its adjacent waters. Based on a two-dimensional "gravest empirical mode" (GEM), a gravitational potential (φ, a vertically integrated variable) was used as proxy for the vertical temperature profiles TG(p, φ).φ integrated from 8 MPa to the surface shows a close relationship with the temperature, except in the deep layer greater than 15 MPa, which was caused by the bimodal deep water in the region. The GEM temperature profiles successfully revealed the bimodality of the Luzon Strait deep water, that disparate hydrophic vertical profiles can produce distinct specific volume anomaly (δ) in the SCS and the western Philippine Sea (WPS), but failed in the Luzon Strait, where different temperature profiles may produce a same δ. A significant temperature divergence between the SCS water and the WPS water confirmed that the bimodal structure is strong. The deepwater bifurcation starts at about 15 MPa, and gets stronger with increasing depth . As the only deep channel connecting the bimodal-structure waters, water column characteristics in the Luzon Strait is in between, but much closer to the SCS water because of its better connectivity with the SCS. A bimodal temperature structure below 15 MPa reveals that there was a persistent baroclinic pressure gradient driving flow through the Luzon Strait. A volume flux predicted through the Bashi Channel with the hydraulic theory yields a value of 5.62×106 m3/s using all available profiles upstream and downstream of the overflow region, and 4.03×106 and 2.70×106 m3/s by exclusively using the profiles collected during spring and summer, respectively. No volume flux was calculated during autumn and winter because profiles are only available for the upstream of the Bashi Channel during the corresponding period.-
Key words:
- Luzon Strait /
- historical hydrocasts /
- gravest empirical mode /
- deep water /
- bimodality /
- volume flux
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Book Jeffrey W, Wimbush Mark, Imawaki Shiro, et al. 2002. Kuroshio temporal and spatial variations south of Japan determined from inverted echo sounder measurements. J Geophys Res, 107: doi: 10.1029/2001JC000795 Broecker Wallace S, Patzert William C, Toggweiler John R, et al. 1986. Hydrography, chemistry, and radioisotopes in the southeast Asian basins. J Geophys Res, 91: 14345-14354 Chang Ya-Ting, Hsu Wei-Lun, Tai Jen-Hua, et al. 2010. Cold deep water in the South China Sea. J Oceanogr, 66: 183-190 Chen Chen-Tung Arthur, Wang Shu-Lun, Wang Bing-Jye, et al. 2001. Nutrients budgets for the South China Sea basin. Marine Chemistry, 75: 281-300 Gong Gwo-Ching, Liu Kon Kee, Liu Cho-Teng, et al. 1992. The chemical hydrography of the South China Sea west of Luzon and a comparison with the west Philippine Sea. Terrestrial, Atmospheric and Oceanic Sciences, 3: 587-602 Killworth P D. 1994. On the reduced-gravity flows through sills. Geophys Astrophys Fluid Dyn, 75: 91-106 Liu Qinyan, Huang Ruixin, Wang Dongxiao, et al. 2006. Interplay between the Indonesian throughflow and the South China Sea throughflow. Chinese Science Bulletin, 51: 50-58 Liu Qinyan, Wang Dongxiao, Zhou Wen, et al. 2010. Covariation of the Indonesian throughflow and South China Sea throughflow associated with the 1976/77 regime shift. Advances in Atmospheric Sciences, 27(1): 87-94 Meinen Christopher S, Watts D Randolph. 2000. Vertical structure and transport on a transect across the North Atlantic Current near 42°N: time series and mean. J Geophys Res, 105: 21869-21891 Meinen Christopher S, Luther Douglas S, Baringer Molly O. 2008. Structure, transport and potential vorticity of the Gulf Stream at 68°W: revisiting older data sets with new techniques. Deep-Sea Res, 56: 41-60 Mitchell D A, Wimbush M, Watts D R. 2004. The residual GEM technique and its application to the southwestern Japan/East Sea. J Atmos Oceanic Technol, 21: 1895-1909 Park Jae-Hun, Andres Magdalena, Martin Paul J, et al. 2006. Secondmode internal tides in the East China Sea deduced from historical hydrocasts and a model. Geophysical Research Letters, 33: L05602, doi: 10.1029/2005GL024732 Park Jae-Hun, Watts D Randolph, Tracey Karen L. 2005. A multi-index GEM technique and its application to the Japan/East Sea. J Atmos Oceanic Technol, 22: 1282-1293 Qu Tangdong. 2002. Evidence of water exchange between the South China Sea and the Pacific through the Luzon Strait. Acta Oceanologica Sinica, 21: 175-185 Qu Tangdong, Girton James B, Whitehead J A. 2006. Deep water overflow through Luzon Strait. Journal of Geophysical Research, 111: C01002, doi: 10.1029/2005JC003139 Qu Tangdong, Mitsudera Humio, Yamagata Toshio. 2000. Intrusion of the North Pacific waters into the South China Sea. Journal of Geophysical Research, 105: 6415-6424 Sun Che, Watts D Randolph. 2001. A circumpolar gravest empirical mode for the Southern Ocean hydrography. J Geophys Res, 106: 2833-2855 Tian Jiwei, Qu Tangdong. 2012. Advances in research on the deep South China Sea circulation. Chinese Science Bulletin, 57(24): 3115- 3120, doi: 10.1007/s11434-012-5269-x Tian Jiwei, Yang Qingxuan, Liang Xinfeng, et al. 2006. Observation of Luzon Strait transport. Geophysical Research Letters, 33: L19607, doi: 10.1029/2006GL026272 Wang Dongxiao, Liu Qinyan, Huang Ruixin, et al. 2006. Interannual variability of the South China Sea throughflow inferred from wind data and an ocean data assimilation product. Geophysical Research Letters, 33: L14605, doi: 10.1029/2006GL026316 Wang Guihua, Xie Shang-Ping, Qu Tangdong, et al. 2011. Deep South China Sea circulation. Geophysical Research Letters, 38: L05601, doi: 10.1029/2010GL046626 Watts D Randolph, Sun Che, Rintoul Steve. 2001. A two-dimensional gravest empirical mode determined from hydrographic observations in the subantarctic front. J Phys Oceanogr, 31: 2186-2209 Whitehead J A. 1998. Topographic control of oceanic flows in deep passages and straits. Rev Geophys, 36: 423-440 Wyrtki Klaus. 1961. Physical oceanography of the southeast Asian waters. La Jolla, California: Naga Rep 2, Scientific results of marine investigation of the South China sea and the Gulf of Thailand, 195 Yang Qingxuan, Tian Jiwei, Zhao Wei. 2010. Observation of Luzon Strait transport in summer 2007. Deep-Sea Res, 57: 670-676 Zhang Yanwei, Moum James N. 2010. Inertial-convective subrange estimates of thermal variance dissipation rate from moored temperature measurements. J Atmos Oceanic Technol, 27: 1950-1959
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