利用地震海洋学方法估算南海中尺度涡的地转流速
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摘要
中尺度涡是重要的海洋学现象,它在很大程度上影响着海洋内部的能量传递过程.由于传统海洋学观测手段的固有局限性,一直以来对中尺度涡观测和研究的程度都比较低.地震海洋学的诞生和发展为海洋学观测提供了一个全新的手段.对南海的历史地震数据重新处理后,我们首次在本研究海域的地震剖面上看到了透镜状结构.它位于南海西南次海盆(～113.6°E,11.4°N),中心深度约为450m,中心厚度约为300m,半径约为55～65km,具有典型的中尺度涡特征,综合解释为反气旋.我们利用地震海洋学方法估算了地转剪切,结合来自于卫星高度数据的海表面地转流速度进一步得到了绝对流速的垂向剖面.结果显示,流速的最大值约为0.7m/s,出现在400～450m处,对应于涡旋的中心深度;西北部分为正,东南部分为负,整体呈现出顺时针的转动方向,说明了它是一个反气旋结构.
Mesoscale eddy is an important oceanographic phenomenon which significantly affects the whole oceanic energy budget.Due to the inherent limitations of traditional oceanographic observation methods,the degree of observations and research of mesoscale eddy has been relatively low.Seismic Oceanography,a new interdisciplinary subject of reflection seismology and physical oceanography,provides a new approach for oceanographic observations.After reprocessing of a legacy seismic data acquired in the South China Sea,a lens-like structure was detected for the first time in this region from seismic profiles.It is located in the Southwestern sub-basin of South China Sea(~113.6°E,11.4°N) with the equilibrium depth of about 450 m,center thickness of about 300 m and radius of 55~65 km,showing typical characteristics of a mesoscale eddy.With the additional information of sea level anomalies(SLA) and sea-surface geostrophic current from AVISO,the lens-like structure was interpreted as an anticyclonic mesoscale eddy.Geostrophic shear was also estimated using the seismic oceanographic method.Absolute values of geostrophic velocity were determined by integrating the shear over depth from a known level,i.e.sea surface values from AVISO.The results show that the maximum value of geostrophic velocity is about 0.7 m/s,distributed in the depth range of 400~450 m,corresponding to the equilibrium depth.Of this eddy,the northwest part is positive while the southeast part is negative,showing a clockwise rotation as a whole,indicating that it is an anticyclonic structure.
Mesoscale eddy is an important oceanographic phenomenon which significantly affects the whole oceanic energy budget.Due to the inherent limitations of traditional oceanographic observation methods,the degree of observations and research of mesoscale eddy has been relatively low.Seismic Oceanography,a new interdisciplinary subject of reflection seismology and physical oceanography,provides a new approach for oceanographic observations.After reprocessing of a legacy seismic data acquired in the South China Sea,a lens-like structure was detected for the first time in this region from seismic profiles.It is located in the Southwestern sub-basin of South China Sea(~113.6°E,11.4°N) with the equilibrium depth of about 450 m,center thickness of about 300 m and radius of 55~65 km,showing typical characteristics of a mesoscale eddy.With the additional information of sea level anomalies(SLA) and sea-surface geostrophic current from AVISO,the lens-like structure was interpreted as an anticyclonic mesoscale eddy.Geostrophic shear was also estimated using the seismic oceanographic method.Absolute values of geostrophic velocity were determined by integrating the shear over depth from a known level,i.e.sea surface values from AVISO.The results show that the maximum value of geostrophic velocity is about 0.7 m/s,distributed in the depth range of 400~450 m,corresponding to the equilibrium depth.Of this eddy,the northwest part is positive while the southeast part is negative,showing a clockwise rotation as a whole,indicating that it is an anticyclonic structure.
引文
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[20]Song H B,Bai Y,Pinheiro L M,et al.Analysis of oceaninternal waves imaged by multichannel reflection seismics,using Ensemble Empirical Mode Decomposition.Journal ofGeophysics and Engineering,2012,9(3):302-311,doi:10.1088/1742-2132/9/3/302.
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[22]Sheen K L,White N J,Caulfield C P,et al.Estimatinggeostrophic shear from seismic images of oceanic structure.Journal of Atmospheric and Oceanic Technology,2011,28(9):1149-1154.
[23]Hwang C,Chen S A.Circulations and eddies over the SouthChina Sea derived from TOPEX/Poseidon altimetry.Journalof Geophysical Research,2000,105(C10):23943-23965.
[24]Wang G H,Su J,Chu P C.Mesoscale eddies in the SouthChina Sea observed with altimeter data.Geophys.Res.Lett.,2003,30(21):2121,doi:10.1029/2003GL018532.
[25]Krahmann G,Papenberg C,Brandt P,et al.Evaluation ofseismic reflector slopes with a Yoyo-CTD.Geophys.Res.Lett.,2009,36:L00D02,doi:10.1029/2009GL038964.
[26]Zhu X H,Park J H,Wimbush M,et al.Comment on“Current system east of the Ryukyu Islands”by A.Naganoet al.Journal of Geophysical Research,2008,113:C03020,doi:10.1029/2007JC004458.
[2]宋海斌,董崇志,陈林等.用反射地震方法研究物理海洋-地震海洋学简介.地球物理学进展,2008,23(4):1156-1164.Song H B,Dong C Z,Chen L,et al.Reflection seismicmethods for studying physical oceanography:Introduction ofseismic oceanography.Progress in Geophysics(in Chinese),2008,23(4):1156-1164.
[3]Song H B,Pinheiro L M,Ruddick B,et al.SeismicOceanography:a new geophysical tool to investigate thethermohaline structure of the oceans.//Marcelli M ed.Oceanography.In Tech Press,2012:113-128.
[4]Ruddick B,Song H B,Dong C Z,et al.Water columnseismic images as maps of temperature gradient.Oceanography,2009,22(1):192-205.
[5]宋海斌,Pinheiro L,王东晓等.海洋中尺度涡与内波的地震图像.地球物理学报,2009,52(11):2775-2780.Song H B,Pinheiro L,Wang D X,et al.Seismic images ofocean meso-scale eddies and internal waves.Chinese J.Geophys.(in Chinese),2009,52(11):2775-2780.
[6]Biescas B,Sallarès V,PelegríJ L,et al.Imaging meddyfinestructure using multichannel seismic reflection data.Geophys.Res.Lett.,2008,35:L11609,doi:10.1029/2008GL033971.
[7]Song H B,Pinheiro L M,Ruddick B,et al.Meddy,spiralarms,and mixing mechanisms viewed by seismic imaging inthe Tagus Abyssal Plain(SW Iberia).Journal of MarineResearch,2011,69(4-6):827-842.
[8]Buffett G G,Biescas B,PelegríJ L,et al.Seismic reflectionalong the path of the Mediterranean Undercurrent.ContinentalShelf Research,2009,29(15):1848-1860.
[9]Nandi P,Holbrook W S,Pearse S,et al.Seismic reflectionimaging of water mass boundaries in the Norwegian Sea.Geophys.Res.Lett.,2004,31:L23311,doi:10.1029/2004GL021325.
[10]Biescas B,Armi L,Sallarès V,et al.Seismic imaging ofstaircase layers below the Mediterranean Undercurrent.Deep-Sea Research Part I:Oceanographic Research Papers,2010,57(10):1345-1353.
[11]Fer I,Nandi P,Holbrook W S,et al.Seismic imaging of athermohaline staircase in the western tropical North Atlantic.Ocean Sci.,2010,6(3):621-631.
[12]黄兴辉,宋海斌,Pinheiro L M等.利用反射地震数据和XBT数据联合反演海水的温盐颁布.地球物理学报,2011,54(5):1293-1300.Huang X H,Song H B,Pinheiro L M,et al.Oceantemperature and salinity distributions inverted from combinedreflection seismic and XBT data.Chinese J.Geophys.(inChinese),2011,54(5):1293-1300.
[13]宋洋,宋海斌,陈林等.利用地震数据反演海水温盐结构.地球物理学报,2010,53(11):2696-2702.Song Y,Song H B,Chen L,et al.Sea water thermohalinestructure inversion from seismic data.Chinese J.Geophys.(in Chinese),2010,53(11):2696-2702.
[14]Wood W T,Holbrook W S,Sen M K,et al.Full waveforminversion of reflection seismic data for ocean temperatureprofiles.Geophys.Res.Lett.,2008,35:L04608,doi:10.1029/2007GL032359.
[15]Papenberg C,Klaeschen D,Krahmann G,et al.Oceantemperature and salinity inverted from combined hydrographic andseismic data.Geophys.Res.Lett.,2010,37:L04601,doi:10.1029/2009GL042115.
[16]董崇志,宋海斌,郝天珧等.南海东北部海洋内波的反射地震研究.地球物理学报,2009,52(8):2050-2055.Dong C Z,Song H B,Hao T Y,et al.Studying of oceanicinternal wave spectra in the Northeast South China Sea fromseismic reflections.Chinese J.Geophys.(in Chinese),2009,52(8):2050-2055.
[17]Holbrook W S,Fer I.Ocean internal wave spectra inferredfrom seismic reflection transects.Geophys.Res.Lett.,2005,32:L15604,doi:10.1029/2005GL023733.
[18]Krahmann G,Brandt P,Klaeschen D,et al.Mid-depthinternal wave energy off the Iberian Peninsula estimated fromseismic reflection data.Journal of Geophysical Research,2008,113:C12016,doi:10.1029/2007JC004678.
[19]宋海斌,拜阳,董崇志等.南海东北部内波特征———经验模态分解方法应用初探.地球物理学报,2010,53(2):393-400.Song H B,Bai Y,Dong C Z,et al.A preliminary study ofapplication of Empirical Mode Decomposition method inunderstanding the features of internal waves in thenortheastern South China Sea.Chinese J.Geophys.(inChinese),2010,53(2):393-400.
[20]Song H B,Bai Y,Pinheiro L M,et al.Analysis of oceaninternal waves imaged by multichannel reflection seismics,using Ensemble Empirical Mode Decomposition.Journal ofGeophysics and Engineering,2012,9(3):302-311,doi:10.1088/1742-2132/9/3/302.
[21]Sheen K L,White N J,Hobbs R W,et al.Estimatingmixing rates from seismic images of oceanic structure.Geophys.Res.Lett.,2009,36:L00D04,doi:10.1029/2009GL040106.
[22]Sheen K L,White N J,Caulfield C P,et al.Estimatinggeostrophic shear from seismic images of oceanic structure.Journal of Atmospheric and Oceanic Technology,2011,28(9):1149-1154.
[23]Hwang C,Chen S A.Circulations and eddies over the SouthChina Sea derived from TOPEX/Poseidon altimetry.Journalof Geophysical Research,2000,105(C10):23943-23965.
[24]Wang G H,Su J,Chu P C.Mesoscale eddies in the SouthChina Sea observed with altimeter data.Geophys.Res.Lett.,2003,30(21):2121,doi:10.1029/2003GL018532.
[25]Krahmann G,Papenberg C,Brandt P,et al.Evaluation ofseismic reflector slopes with a Yoyo-CTD.Geophys.Res.Lett.,2009,36:L00D02,doi:10.1029/2009GL038964.
[26]Zhu X H,Park J H,Wimbush M,et al.Comment on“Current system east of the Ryukyu Islands”by A.Naganoet al.Journal of Geophysical Research,2008,113:C03020,doi:10.1029/2007JC004458.
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