摘要
陆架波的研究对于加深陆架海洋动力学的理解具有重要意义,同时对于提高沿岸水位、流速预报的准确性具有实际应用价值。中国的陆架波研究,虽然自20世纪80年代以来有过相应的研究,但研究相对薄弱,特别是在动力机制及其在实际预报的应用方面,几乎没有相关的工作。东海作为世界上陆架最宽阔的海域之一,陆架波运动是本海区的重要海洋学现象之一,有必要对东海陆架波做进一步深入的研究。
通过理论分析、数值求解及对实测数据的分析表明:在东海存在自由陆架波和强迫陆架波,这种低频的波动是除潮运动以外东海重要的动力学现象之一。
通过求取东海宽陆架地形条件下自由陆架波的解析解,分析了东海自由波动的频散关系。表明在东海陆架上存在一系列的低频波动,此即陆架波各种不同模态。由观测数据分析得到的频散关系能很好的吻合到理论频散图上。理论及计算结果表明在东海宽而缓的地形下,正压Kelvin波占陆架波模态的主导地位,同时存在第一模态地形陆架波(SW1)和第二模态地形陆架波(SW2)。
利用经验模态分解(EMD)方法分析实测水位,发现东海存在2~10天周期不等的低频波动,此波动沿东海沿岸自北向南传播,其相速度与理论得到的相速度相符。
风场对水位的影响甚大,两者之间有很高的相关性。强北风出现对应着水位的急剧升高,这种升高体现在水位的各模态上,水位升高幅度可达几十厘米量级。计算结果表明,强北风引起南向的顺岸流动,此顺岸流对闽浙沿岸流有一定的贡献。
将强迫陆架波理论应用到东海陆架,能很好的模拟东海周期在2~10天的水位及流场波动。总体来看,对顺岸流的模拟结果好于对水位的模拟结果,其原因是水位波动主要由KW模态控制,而顺岸流的波动主要由SW1控制。
东海的低频波动,主要是远处传来的自由波动,但在顺岸向的风速较强时,自由波动被风牵引而转化成强迫波动,同时伴随着水位和顺岸流的剧烈变化。
Continental Shelf Waves (CSW) play an important role in understanding thedynamics of the continental shelf area. It is also of great significance for improvingthe prediction of the sea level and the alongshore current. Although studies on CSWstarted as early as1980s, the research on this topic is still quite rare, especially for thegeneration mechanism and application in sea level and alongshore current predictionin the East China Sea (ECS) which is one of the widest continental shelves in theworld.
Based on analytical theory, numerical solution and data analysis, this workconfirms the existence of free and forced CSW in ECS. This low-frequency waveactivity is one of the most important dynamical processes in ECS.
The dispersion relation in ECS is obtained which shows that there are a set oflow-frequency waves as different modes of CSW. The dispersion relation derivedfrom observation agrees quite well with the analytical results. Analytical theory andnumerical solution indicate that barotropic Kelvin wave plays the dominant role inECS, and the first (SW1) and second (SW2) modes of CSW Shelf Wave are alsoimportant.
By employing the Empirical Mode Decomposition (EMD) scheme, we find thatCSW does exist in ECS, and the periods are from2to10days.
The low-frequency sea level fluctuation is closely related with wind forcings.Large sea level rise always follows the strong north wind in ECS. The amplitude ofthe sea level variation can reach tens centimeters. Numerical solution indicates thatthe alongshore wind can induce a downwind alongshore current.
The wind-forced CSW theory is applied in ECS. Numerical results show that the calculated results can successfully reproduce the sea level variation and downwindflow. The model can simulate alongshore current better than that of the sea level,because the sea level vaariation is mainly due to the Kelvin waves (KW) while thealongshore current is controlled by the Shelf Waves (SW1).
The low-frequency fluctuation in ECS is mainly the free wave. And the freewave can be induced into force wave in the condition of strong alongshore wind.
引文
[1]冯士莋,李凤岐,李少菁等.海洋科学导论.1999, p:181
[2]秦曾灏,刘秦玉,摩擦和β效应对地形拦截波的影响.海洋与湖沼,1988.19(1): p.8-17.
[3]王佳,袁业立,潘增第,陆架波的数值研究及分析.海洋学报,1988.10(6): p.666-677.
[4]陈大可,苏纪兰,中国沿岸陆架波的初步研究.海洋学报,1987.9(1): p.1-15.
[5]孔祥德,尹逊福,李繁华,东海陆架波及其对黑潮的影响.海洋学报,1992.14(5): p.8-14.
[6]冯士莋, f-平面上的宽陆架诱导阻尼波.海洋学报,1979.1(2): p.177-192.
[7] Mysak, L.A., Recent advances in shelf wave dynamics. Rev. Geophys.,1980.18(1): p.211-241.
[8] Gill, A.E., Atmosphere-ocean dynamics. London NW1: Academic Pr,1982.408-415
[9] Gill, A.E. and A.J. Clarke, Wind-induced upwelling, coastal currents and sea-level changes.Deep Sea Research and Oceanographic Abstracts,1974.21(5): p.325-345.
[10] Hamon, B.V., The Spectrums of Mean Sea Level at Sydney, Coff's Harbour, and Lord HoweIsland. J. Geophys. Res.,1962.67(13): p.5147-5155.
[11] Robinson, A.R., Continental Shelf Waves and the Response of Sea Level to Weather Systems.J. Geophys. Res.,1964.69(2): p.367-368.
[12] LeBlond, P.H. and L.A. Mysak, Waves in the Ocean. Vol.20.1980: Elsevier Science Ltd.
[13] LeBlond, P.H. and L.A.Mysak, Trapped coastal waves and their role in shelf dynamics. inThe Sea,1977.6: p.459-495.
[14] Huthnance, J.M., On coastal trapped waves over a continental shelf. J. Fluid Mech.,1975.69.
[15] Mysak, L.A., Edgewaves on a gently sloping continental shelf of finite width. J. Mar. Res.,1968.26: p.24-33.
[16] Csanady, G.T., Topographic Waves in Lake Ontario. Journal of Physical Oceanography,1976.6(1): p.93-103.
[17] Ball, F.K., Edge waves in an ocean of finite depth. Deep Sea Research,1967.14: p.79-88.
[18] Huntley, D.A. and A.J. Bowen, Field observations of edge waves. Nature,1973.243: p.160-172.
[19]Buchwald, V. T., J.K.Adams.1968. The propagation of continental shelf waves.Proc.Roy.Soc.Ser.A,305,235-250.
[20] Snodgrass, F.E., W.H. Munk, and G.R. Miller, Long period waves over California'scontinental borderland J. Mar. Res.,1962.20: p.3-30.
[21] Longuet-Higgins, M., On the trapping of wave energy round islands. J. Fluid Mech,1967.29(4): p.781-821.
[22] Longuet-Higgins, M., On the trapping of long-period waves round islands. J. Fluid Mech,1969.37(part4): p.773-784.
[23] Summerfield, W., Circular islands as resonators of long-wave energy. PhilosophicalTransactions of the Royal Society of London. Series A, Mathematical and PhysicalSciences,1972.272(1225): p.361.
[24] Pizarro, O. and G. Shaffer, Wind-Driven, Coastal-Trapped Waves off the Island of Gotland,Baltic Sea. Journal of Physical Oceanography,1998.28(11): p.2117-2129.
[25] Brink, K.H., Island-trapped waves, with application to observations off Bermuda. Dynamicsof Atmospheres and Oceans,1999.29(2-4): p.93-118.
[26] Kajiura, K., Effect of stratification on long period trapped waves on the shelf. Journal ofOceanography,1974.30(6): p.271-281.
[27] Allen, J.S., Coastal Trapped Waves in a Stratified Ocean. Journal of Physical Oceanography,1975.5(2): p.300-325.
[28] Wang, D.-P., Coastal Trapped Waves in a Baroclinic Ocean. Journal of PhysicalOceanography,1975.5(2): p.326-333.
[29] Wright, D. and L. Mysak, Coastal trapped waves, with application to the Northeast PacificOcean. Atmosphere,1977.15(3): p.141-150.
[30] Wang, D.-P. and C.N.K. Mooers, Coastal-Trapped Waves in a Continuously Stratified Ocean.Journal of Physical Oceanography,1976.6(6): p.853-863.
[31] Clarke, A.J., Observational and Numerical Evidence for Wind-Forced Coastal Trapped LongWaves. Journal of Physical Oceanography,1977.7(2): p.231-247.
[32] Huthnance, J.M., On coastal trapped waves-Analysis and numerical calculation by inverseiteration. Journal of Physical Oceanography,1978.8: p.74-92.
[33] Gill, A.E. and E.H. Schumann, The Generation of Long Shelf Waves by the Wind. Journal ofPhysical Oceanography,1974.4(1): p.83-90.
[34] Hamon, B., Generation of shelf waves on the East Australian coast by wind stress Waves onWater of Variable Depth, D. Provis and R. Radok, Editors.1977, Springer Berlin/Heidelberg. p.220-220.
[35] Martínez, J.A. and J.S. Allen, A Modeling Study of Coastal-Trapped Wave Propagation in theGulf of California. Part I: Response to Remote Forcing. Journal of PhysicalOceanography,2004.34(6): p.1313-1331.
[36] Brooks, D.A., Coupling of the Middle and South Atlantic Bights by Forced Sea LevelOscillations. Journal of Physical Oceanography,1979.9(6): p.1304-1311.
[37] Wang, D.-P. and C.N.K. Mooers, Long Coastal-Trapped Waves off the West Coast of theUnited States, Summer1973. Journal of Physical Oceanography,1977.7(6): p.856-864.
[38] Brink, K.H., The Effect of Bottom Friction on Low-Frequency Coastal Trapped Waves.Journal of Physical Oceanography,1982.12(2): p.127-133.
[39] Battisti, D.S. and B.M. Hickey, Application of Remote Wind-Forced Coastal Trapped WaveTheory to the Oregon and Washington Coasts. Journal of Physical Oceanography,1984.14(5): p.887-903.
[40] Schwing, F.B., L.-Y. Oey, and J.O. Blanton, Frictional Response of Continental Shelf Waterto Local Wind Forcing. Journal of Physical Oceanography,1985.15(12): p.1733-1746.
[41] Clarke, A.J. and S. Van Gorder, A Method for Estimating Wind-Driven Frictional,Time-Dependent, Stratified Shelf and Slope Water Flow. Journal of PhysicalOceanography,1986.16(6): p.1013-1028.
[42] Mitchum, G.T. and A.J. Clarke, Evaluation of Frictional, Wind-Forced Long-Wave Theory onthe West Florida Shelf. Journal of Physical Oceanography,1986.16(6): p.1029-1037.
[43] Chapman, D.C., Application of wind-forced, long, coastal-trapped wave theory along theCalifornia coast. Journal of geophysical research,1987.92(C2): p.1798-1816.
[44] Webster, I. and D. Holland, A Numerical Method for Solving the Forced BaroclinicCoastal-Trapped Wave Problem of General Form. Journal of Atmospheric and OceanicTechnology,1987.4(1): p.220-226.
[45] Jacobs, G.A., et al., Coastal wave generation in the Bohai Bay and propagation along theChinese coast. Geophys. Res. Lett.,1998.25(6): p.777-780.
[46] Hsueh, Y. and I.-C. Pang, Coastally Trapped Long Waves in the Yellow Sea. Journal ofPhysical Oceanography,1989.19(5): p.612-625.
[47] Clarke, A.J. and K. Brink, The response of stratified, frictional flow of shelf and slope watersto fluctuating large-scale, low-frequency wind forcing. Journal of Physical Oceanography,1985.15(4): p.439-453
[48]林美华,东海海底地形的特征.海洋科学,1981.01: p.24-27.
[49]远东巡洋舰-【远东述评】东海油气争端,中日或有一战!-中华网博客
[50]中国大百科全书-大气海洋水位卷.1987,北京-上海:.中国大百科全书出版社
[51]孙湘平,中国近海区域海洋.2ed.2008,海洋出版社.
[52]王佳,环流和陷波的数值与理论研究及其在东中国海的应用,[博士学位论文].青岛:中国科学院海洋研究所,1987.
[53]陈红霞,东海南部流-涡结构分析与动力机制研究,[博士学位论文].青岛:中国科学院研究生院,2008.
[54] Jordi, A., et al., Coastal trapped waves in the northwestern Mediterranean. Continental ShelfResearch,2005.25: p.185-196.
[55] Hamon, B.V., Continental Shelf Waves and the Effects of Atmospheric Pressure and WindStress on Sea Level. J. Geophys. Res.,1966.71(12): p.2883-2893.
[56] Mooers, C.N.K. and R.L. Smith, Continental Shelf Waves off Oregon. J. Geophys. Res.,1968.73(2): p.549-557.
[57] Cutchin, D.L. and R.L. Smith, Continental Shelf Waves: Low-Frequency Variations in SeaLevel and Currents Over the Oregon Continental Shelf. Journal of Physical Oceanography,1973.3(1): p.73-82.
[58] Huyer, A., et al., Alongshore coherence at low frequencies in currents observed over thecontinental shelf off Oregon and Washington. J. Geophys. Res.,1975.80(24): p.3495-3505.
[59] Kundu, P.K. and J.S. Allen, Some Three-Dimensional Characteristics of Low-FrequencyCurrent Fluctuations near the Oregon Coast. Journal of Physical Oceanography,1976.6(2): p.181-199.
[60] Kundu, P.K., J.S. Allen, and R.L. Smith, Modal Decomposition of the Velocity Field near theOregon Coast. Journal of Physical Oceanography,1975.5(4): p.683-704.
[61] Osmer, S.R. and A. Huyer, Variations in the alongshore correlation of sea level along the WestCoast of North America. J. Geophys. Res,1978.83((C4)): p.1921-1927.
[62] Huyer, A., R.L. Smith, and E.J.C. Sobey, Seasonal differences in low-frequency currentfluctuations over the Oregon continental shelf. Journal of geophysical research,1978.83(C10): p.5077-5089.
[63] Hsieh, W.W., On the Detection of Continental Shelf Waves. Journal of PhysicalOceanography,1982.12(5): p.414-427.
[64] Hsieh, W.W., Observations of Continental Shelf Waves off Oregon and Washington. Journalof Physical Oceanography,1982.12(8): p.887-896.
[65] Christensen Jr, N., R.V. de la Paz, and G.V. Gutiérrez, A study of sub-inertial waves off thewest coast of Mexico. Deep Sea Research Part A. Oceanographic Research Papers,1983.30(8): p.835-850.
[66] Enfield, D.B. and J.S. Allen, The Generation and Propagation of Sea Level Variability Alongthe Pacific Coast of Mexico. Journal of Physical Oceanography,1983.13(6): p.1012-1033.
[67] Martínez, J.A. and J.S. Allen, A Modeling Study of Coastal-Trapped Wave Propagation in theGulf of California. Part I: Response to Remote Forcing. Journal of PhysicalOceanography,2004.34(6): p.1313-1331.
[68] Mysak, L. and B. Hamon, Low-frequency sea level behavior and continental shelf waves offNorth Carolina. J. Geophys. Res.,1969.74(6): p.1397-1405.
[69] Brooks, D.A., Subtidal Sea Level Fluctuations and Their Relation to Atmospheric Forcingalong the North Carolina Coast. Journal of Physical Oceanography,1978.8(3): p.481-493.
[70] Wang, D.-P., Subtidal Sea Level Variations in the Chesapeake Bay and Relations toAtmospheric Forcing. Journal of Physical Oceanography,1979.9(2): p.413-421.
[71] Wang, D.P., Low frequency sea level variability on the Middle Atlantic Bight. Journal ofMarine Research,1979.37: p.683-697.
[72] Schott, F. and W. Düing, Continental Shelf Waves in the Florida Straits. Journal of PhysicalOceanography,1976.6(4): p.451-460.
[73] Brooks, D.A. and C.N.K. Mooers, Wind-forced continental shelf waves in the Florida Current.Journal of geophysical research,1977.82(18): p.2569-2576.
[74] Düing, W., T. LEE, and C. MOOERS, Low-frequency variability in the Florida Current andrelations to atmospheric forcing from1972to1974. Journal of Marine Research,1977.35:p.129-161.
[75] Lee, T.N., F.A. Schott, and R. Zantopp, Florida Current: Low-frequency variability asobserved with moored current meters during April1982to June1983. Science,1985.227(4684): p.298.
[76] Isozaki, I., An investigation on the variations of sea level due to meteorological disturbanceson the coast of Japanese Islands, III. J. Oceanogr. Soc. Japan,1969.25: p.91-102.
[77] Kubota, M., K. Nakata, and Y. Nakamura, Continental shelf waves off the fukushima coastPart I: Observations. Journal of The Oceanographical Society of Japan,1981.37(5): p.267-278.
[78] Csanady, G.T., Topographic Waves in Lake Ontario. Journal of Physical Oceanography,1976.6(1): p.93-103.
[79] Smith, R.L., Poleward Propagating Perturbations in Currents and Sea Levels Along the PeruCoast. J. Geophys. Res.,1978.83(C12).
[80] Picaut, J. and J.M. Verstraete, Propagation of a14.7-Day Wave along the Northern Coast ofthe Guinea Gulf. Journal of Physical Oceanography,1979.9(1): p.136-149.
[81] Kusahara, K. and K.I. Ohshima, Dynamics of the Wind-Driven Sea Level Variation aroundAntarctica. Journal of Physical Oceanography,2009.39(3): p.658-674.
[82] Lascaratos, A. and M. Ga i, Low-Frequency Sea Level Variability in the NortheasternMediterranean. Journal of Physical Oceanography,1990.20(4): p.522-533.
[83] Jacobs, G.A., et al., Coastal wave generation in the Bohai Bay and propagation along theChinese coast. Geophys. Res. Lett.,1998.25(6): p.777-780
[84]赵保仁,曹德明,冬季黄、东海中国沿岸水位的低频波动.海洋与湖沼,1987.1(6): p.400-415.
[85] Chen, X., Z. Wu, and N.E. Huang, The time-dependent intrinsic correlation based on theempirical mode decomposition.
[86] Mitchum, G.T. and A.J. Clarke, Evaluation of Frictional, Wind-Forced Long-Wave Theoryon the West Florida Shelf. Journal of Physical Oceanography,1986.16(6): p.1029-1037.
[87] Large, W.G. and S. Pond, Open Ocean Momentum Flux Measurements in Moderate toStrong Winds. Journal of Physical Oceanography,1981.11(3): p.324-336.
[88] Hsueh, Y. and R.D. Romea, Wintertime Winds and Coastal Sea-Level Fluctuations in theNortheast China Sea. Part I: Observations. Journal of Physical Oceanography,1983.13(11): p.2091-2106.
[89] Brink, K.H., Coastal-Trapped Waves and Wind-Driven Currents Over the Continental Shelf.Annual Review of Fluid Mechanics,1991.23(1): p.389-412.
[90] Koopmans, L.H., The spectral analysis of time series. Vol.22.1995: Academic Pr.
[91] Brink, K.H., Coastal-Trapped Waves and Wind-Driven Currents Over the Continental Shelf.Annual Review of Fluid Mechanics,1991.23(1): p.389-412.
[92] Schumann, E.H. and K.H. Brink, Tidal and subtidal water level fluctuations in the BergEstuary. Transactions of the Royal Society of South Africa,2009.64(2): p.181-188.
[93] Beardsley, R. and S. Lentz, The coastal ocean dynamics experiment collection: Anintroduction. Journal of geophysical research,1987.92(C2): p.1455-1463.