南海东北部海洋内波的反射地震研究
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摘要
已有的内波研究多来自单点的垂直剖面观测资料,但研究内波水平特征的实测资料却非常缺乏.利用反射地震方法研究海水温盐结构,具有高水平分辨率和短时间内对整个海水垂直剖面进行成像的优势,能够弥补传统物理海洋学观测方法的缺陷,为研究海洋内波提供有前景的新手段.本文通过对南海东北部地震剖面的重新处理、分析,认为地震叠加剖面上同相轴呈现的起伏变化反映了内波的总体形态.计算的水平波数能量密度谱与GM76模型谱基本一致,但在低波数段和高波数段中,两者的振幅及斜率存在着一定差异,经分析认为这种差异主要与内潮波和复杂海底地形的强烈非线性相互作用以及内波破碎等因素有关.
Extensive researches about internal waves are mostly from vertical profile observations; however,there are rare in-situ observation data to study horizontal characteristics of internal waves.Compared with the traditional physical oceanographic methods,reflection seismology has several advantages,such as high lateral resolution and the ability of imaging a large ocean profile in short time.Therefore,it is a promising observation technique for internal wave studies,which may make up the defects of traditional observation methods.Results from the reprocessing of a long multi-channel seismic profile in the northeastern margin of the South China Sea reveal clearly coherent undulating reflectors associated with internal waves in the water column.Horizontal wave number spectra of undulating reflectors are calculated and compared with the Garrett-Munk tow spectrum of oceanic internal wave displacements(GM76 spectrum). The results show that internal wave horizontal wave-number spectra are generally consistent with the theoretical GM76 spectrum.However,there are differences in amplitudes and slopes in the low and high wave-number regions between the calculated and theoretical spectra,which are considered to be associated with strong interaction between the internal tides and the complex seafloor topography,and internal wave breaking,etc.
Extensive researches about internal waves are mostly from vertical profile observations; however,there are rare in-situ observation data to study horizontal characteristics of internal waves.Compared with the traditional physical oceanographic methods,reflection seismology has several advantages,such as high lateral resolution and the ability of imaging a large ocean profile in short time.Therefore,it is a promising observation technique for internal wave studies,which may make up the defects of traditional observation methods.Results from the reprocessing of a long multi-channel seismic profile in the northeastern margin of the South China Sea reveal clearly coherent undulating reflectors associated with internal waves in the water column.Horizontal wave number spectra of undulating reflectors are calculated and compared with the Garrett-Munk tow spectrum of oceanic internal wave displacements(GM76 spectrum). The results show that internal wave horizontal wave-number spectra are generally consistent with the theoretical GM76 spectrum.However,there are differences in amplitudes and slopes in the low and high wave-number regions between the calculated and theoretical spectra,which are considered to be associated with strong interaction between the internal tides and the complex seafloor topography,and internal wave breaking,etc.
引文
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[15] 郭朴,方文东,甘子钧等.南海北部大陆坡区的内潮特征.科学通报,2006,51(增刊Ⅱ):15～22Guo P,Fang W D,Gan Z J,et al.The characteristic of internal tides in the slope in northern South China Sea.Chinese Science Bulletin(in Chinese),2006,51(Suppl.Ⅱ):15～22
[16] GarrettC,Munk W.Space-time scales of internal waves.Geophys.Fluid Dyn.,1972,3:225～264
[17] Muller P,Olbers D J.The IWEX spectrum.J.Geophys.Res.,1978,81(C1) :479～500
[18] Nandi P,Holbrook W S,Pearse S,et al.Seismic reflection imaging of water mass boundaries in the Norwegian Sea.Geophys.Res.Lett.,2004,31,L23321,doi:10． 1029/2004GL021325
[19] Biescas B,Sallarès,Pelegri J L,et al.Imaging meddy fine structure using multichannel seismic reflection data.Geophys.Res.Lett.,2008,35:L11609,doi:10． 1029/2008GL033971
[20] Pinheiro L M,Song H B,Ruddick B,et al.Detailed 2-D imaging of the Mediterranean Outflow and Meddies off W Iberia from Multichannel Seismic Data.J.Mar.Syst.,2009,doi:10． 1016/j.jmarsys.2009． 07． 004
[21] Nakamura Y,Noguchi T,Tsuji T,et al.Simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the Kuroshio extension front.Geophys.Res.Lett.,2006,33:L23605,doi:10． 1029/2006GL027437
[22] Ruddick B,Song H B,Dong C Z,et al.Water column seismic images as smoothed maps of dT/dz.Oceanography,2009,22(1) :192～205
[2] 杜涛,吴巍,方欣华.海洋内波的产生与分布.海洋科学,2001,25(4) :25～28Du T,Wu W,Fang X H.The generation and distribution of ocean internal waves.Marine Sciences(in Chinese),2001,25(4) :25～28
[3] Holbrook W S,Paramo P,Pearse S,et al.Thermohaline fine structure in an oceanographic front from seismic reflection profiling.Science,2003,301(8) :821～824
[4] 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) :1156～1164Song H B,Dong C Z,Chen L,et al.Reflection seismic methods for studying physical oceanography:introduction of seismic oceanography.Progress in Geophysics(in Chinese),2008,23(4) :1156～1164
[5] Holbrook W S,Fer I.Ocean internal wave spectra inferred from seismic reflection transects.Geophys.Res.Lett.,2005,32:L15604,doi:10． 1029/2005GL023733
[6] Katz E,Briscoe M G.Vertical coherence of the internal wave field from towed sensors.J.Phys.Oceanogr.,1979,9(3) :518～530
[7] Garrett C,Munk W.Space-time scales of internal waves:progress report.J.Geophys.Res.,1975,80(3) :291～297
[8] Cairns J L,Williams G O.Internal wave observations from a mid-water float,2． J.Geophys.Res.,1976,81((24) :1943～1945
[9] Liu A K,Chang Y S,Hsu M K,et al.Evolution of nonlinear internal waves in the East and South China Seas.J.Geophys.Res.,1998,103(C4) :7997～8008
[10] 张效谦,梁鑫峰,田纪伟.南海北部450 m以浅水层内潮和近惯性运动研究.科学通报,2005,50(18) :2077～2031 Zhang X Q,Liang X F,Tian W.Observation of internal tides and near-inertial motions in the upper 450 m layer of the northern South China Sea.Chinese Science Bulletin,2005,50(24) :2890～2895
[11] 蔡树群,甘子钧.南海北部孤立子内波的研究进展.地球科学进展,2001,16(2) :72～76Cai S Q,Gan Z J.Progress in the study of the internal solition in the northern South China Sea.Advance in Earth Sciences(in Chinese),2001,16(2) :72～76
[12] 蔡树群,甘子钧,龙小敏.南海北部孤立子内波的一些特征和演变.科学通报,2001,46(15) :1245～1250Cai S Q,Gan Z J,Long X M.Some characteristics and evolution of the internal solition in the northern South China Sea.Chinese Science Bulletin,2002,47(1) :21～27
[13] Zhao Z,Klemas V,Zheng Q,et al.Remote sensing evidence for baroclinic tide origin of internal solitary waves in the northeastern South China Sea.Geophys.Res.Lett.,2004,31:L06302,doi:10． 1029/2003GL019077
[14] 方文东,施平,龙小敏等.南海北部孤立内波的现场观测.科学通报,2005,50(13) :1400～1404Fang W D,Shi P,Long X M,et al.Internal solitions in the northern South China Sea from in-situ observations.Chinese Science Bulletin,2005,50(15) :1627～1631
[15] 郭朴,方文东,甘子钧等.南海北部大陆坡区的内潮特征.科学通报,2006,51(增刊Ⅱ):15～22Guo P,Fang W D,Gan Z J,et al.The characteristic of internal tides in the slope in northern South China Sea.Chinese Science Bulletin(in Chinese),2006,51(Suppl.Ⅱ):15～22
[16] GarrettC,Munk W.Space-time scales of internal waves.Geophys.Fluid Dyn.,1972,3:225～264
[17] Muller P,Olbers D J.The IWEX spectrum.J.Geophys.Res.,1978,81(C1) :479～500
[18] Nandi P,Holbrook W S,Pearse S,et al.Seismic reflection imaging of water mass boundaries in the Norwegian Sea.Geophys.Res.Lett.,2004,31,L23321,doi:10． 1029/2004GL021325
[19] Biescas B,Sallarès,Pelegri J L,et al.Imaging meddy fine structure using multichannel seismic reflection data.Geophys.Res.Lett.,2008,35:L11609,doi:10． 1029/2008GL033971
[20] Pinheiro L M,Song H B,Ruddick B,et al.Detailed 2-D imaging of the Mediterranean Outflow and Meddies off W Iberia from Multichannel Seismic Data.J.Mar.Syst.,2009,doi:10． 1016/j.jmarsys.2009． 07． 004
[21] Nakamura Y,Noguchi T,Tsuji T,et al.Simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the Kuroshio extension front.Geophys.Res.Lett.,2006,33:L23605,doi:10． 1029/2006GL027437
[22] Ruddick B,Song H B,Dong C Z,et al.Water column seismic images as smoothed maps of dT/dz.Oceanography,2009,22(1) :192～205
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