长江口外羽状流水体中的垂向混合与层化的观测与分析

摘要/Abstract

摘要： 摘要：
2002年9月17日17：00至18日17：00，在长江口外E4站位 (122°40′8″E, 30°59′17″N)，采用300 kHz声学多普勒流速剖面仪(ADCP)和温盐深仪(CTD)测得连续的水位、流速大小、流向、电导(盐度)和温度等水文资料.基于这些资料，通过文献中相应的公式，估算出水体的密度(ρ)、浮力频率(N)和梯度Richardson数(Ri)，并绘制成水流流速分量、盐度、温度、ρ、N和Ri的垂线分布，从而对该站位羽状流水体中的垂向混合与层化进行了研究.结果表明：① 东西向流速分量大小范围为-0.36~0.61 m/s，南北向流速大小范围为-0.59~0.39 m/s.涨急、落急和落憩，流速分量在垂向上变化均不大；涨憩时，表、中、底层流速存在显著差异.② 涨急、涨憩，从表层至底层，盐度随着水深的增加而增大，温度随着水深的增加而减小；落憩，温度在中层达到最大；落急，水体出现显著的密度跃层.③ 该站位表层水体的N均较小，基本在10-3 s-1量级，水体垂向混合较好；中、下层水体的N出现10-2 s-1量级，混合相对较弱.④ 该站位水体垂向混合强度呈现涨、落潮周期变化：涨急、涨憩，Ri范围在10-2 ~101量级，混合较好；落急，Ri在中下层水体出现102量级，水体出现显著层化；落憩，整个水体的Ri大部分都小于临界值0.25，水体混合最充分.
关键词：
长江口外；羽状流；浮力频率；梯度 Richardson数；混合；层化
中图分类号： P 731.26
文献标志码： A

Abstract: A field study was conducted at Station E4 (122°40′8″E, 30°59′17″N) within the plume outside the Changjiang River estuary from 17:00, Sept. 17 to 17:00, Sept. 18, 2002. Based on the relevant equations available in the literature, density, buoyancy frequency and the gradient Richardson number were estimated from flow velocity (speed and direction)，conductivity (salinity) and temperature obtained by 300 kHz Acoustic Doppler Current Profiler (ADCP) and ConductanceTemperatureDepth Probe (CTD). Vertical profiles of velocity components, salinity, temperature, density, buoyancy frequency and the gradient Richardson number were plotted so as to elucidate the vertical mixing and stratification within the plume outside the Changjiang River estuary. Results show that ① the WE component of velocity varies from -0.36 to 0.61 m/s, the NS component of velocity varies from -0.59 to 0.39 m/s. Velocity components vertically vary little during maximum flood tide, maximum ebb tide and low slack water while during high slack water velocity components show significant difference from the surface layer to the bottom layer. ② Salinity increases while temperature decreases with water depth during maximum flood tide and high slack water from the surface layer to the bottom layer. Maximum temperature occurs at the middepth during low slack water. A significant pycnocline appears during maximum ebb tide. ③ Waters within the plume of the Changjiang River estuary seem to be wellmixed with small values of the buoyancy frequency (in the order of 10-3 s-1) at the upper layer and weaklymixed with relative large values (in the order of 10-2 s-1) at the mid and lower layers. ④ The intensity of vertical mixing displays flood/ebb tidal variability: relative weaklymixed with the gradient Richardson number in the order of 10-2~101 during maximum flood tide and high slack water, intense stratification with large values of gradient Richardson number (in the order of 102) at the mid and lower layers during maximum ebb tide. Most values of the gradient Richardson number are smaller than the critical value 0.25, suggesting that waters within the plume are well mixed during low slack water.

Key words: Changjiang River estuary, plume, buoyancy frequency, gradient Richardson number, mixing, stratification

倪智慧1, 陈辉1, 董礼先2, 时钟1, 王殿志1, 翟强1. 长江口外羽状流水体中的垂向混合与层化的观测与分析[J]. 上海交通大学学报（自然版）, 2012, 46(11): 1862-1873.

NI Zhi-Hui-1, CHEN Hui-1, DONG Li-Xian-2, SHI Zhong-1, WANG Dian-Zhi-1, DI Qiang-1. Measurement and Analysis of Vertical Mixing and Stratification Within the Plume Outside the Changjiang River Estuary[J]. Journal of Shanghai Jiaotong University, 2012, 46(11): 1862-1873.

参考文献

［1］

Garvine R W. Estuaries, geophysics and the environment ［M］. Washington DC: National Academy of Sciences, 1977.
［2］Bowman M J, Iverson R C. Estuarine and plume fronts ［C］ //

Oceanic Fronts in Coastal Processes. Berlin: SpringerVerlag, 1978: 87104.
［3］Bowden K F. Physical oceanography of coastal waters ［M］. Chichester: Ellis Horwood John Wiley & Sons, 1983.
［4］Nash J D, Moum J N. River plumes as a source of large amplitude internal waves in the coastal ocean ［J］. Nature, 2005, 437: 400403.
［5］Bowden K F. Estuaries and coastal waters ［J］. Proceedings of the Royal Society of London, 1962, A 265 (1322): 320325.
［6］Arons A B, Stommel H. A mixinglength theory of tidal flushing ［J］. Transactions of American Geophysical Union, 1951, 32: 419421.
［7］Stommel H, Farmer H G. On the nature of estuarine circulation ［M］. Woods Hole, USA: WHOI Technical Report 5288, 1952.
［8］Bowden K F. The mixing processes in a tidal estuary ［J］. International Journal of Air and Water Pollution, 1963, 7: 343356.
［9］Nepf H M, Geyer W R. Intratidal variations in stratification and mixing in the Hudson estuary ［J］. Journal of Geophysical Research, 1996, 101(C5): 12,07912,086.
［10］Chant R J, Wilson R E. Internal hydraulics and mixing in a highly stratified estuary ［J］. Journal of Geophysical Research, 2000, 105(6): 14, 21514, 222.
［11］Stommel H, Farmer H G. Control of salinity in an estuary by a transition ［J］. Journal of Marine Research, 1953, 11: 1320.
［12］Pritchard D W. Salinity distribution and circulation in the Chesapeake Bay estuarine system ［J］. Journal of Marine Research, 1952, 11: 106123.
［13］Pritchard D W. A study of the salt balance in a coastal plain estuary ［J］. Journal of Marine Research, 1954, 13: 133144.
［14］Pritchard D W. The dynamic structure of a coastal plain estuary ［J］. Journal of Marine Research, 1956, 15: 3342.
［15］Rattray M Jr, Hansen D V. A similarity solution for the circulation in an estuary ［J］. Journal of Marine Research, 1962, 20: 121133.
［16］Hansen D V, Rattray M Jr. Gravitational circulation in straits and estuaries ［J］. Journal of Marine Research, 1965, 23: 104122.
［17］Peters H. Broadly distributed and locally enhanced turbulent mixing in a tidal estuary ［J］. Journal of Physical Oceanography, 2003, 33: 19671977.
［18］Chen F, MacDonald D G. Role of mixing in the structure and evolution of a buoyant discharge plume ［J］. Journal of Geophysical Research, 2006, 111, C11002.
［19］MacDonald D G, Goodman L, Hetland R D. Turbulent dissipation in a nearfield river plume: a comparison of control volume and microstructure observations with a numerical model ［J］. Journal of Geophysical Research, 2007, 112: C07026.
［20］Geyer W R, Scully M E, Ralston D K. Quantifying vertical mixing in estuaries ［J］. Environmental Fluid Mechanics, 2008, 8: 495509.
［21］Fischer H B. Mixing and dispersion in estuaries［J］. Annual Review of Fluid Mechanics, 1976, 8: 107133.
［22］Fischer H B, List E J, Koh R C Y, et al. Mixing in estuaries ［C］ // Mixing in Inland and Coastal Waters.［s.l.］: Academic Press, 1979: 229278.
［23］Ippen A T. Estuary and coastline hydrodynamics ［M］. New York, McGraw Hill, 1966.
［24］Lewis R. Dispersion in estuaries and coastal waters ［M］. West Sussex, England: John Wiley & Sons, 1997.
［25］Chanson H. Mixing in estuaries ［C］ // Environmental Hydraulics of Open Channel Flows. ［s.l.］:Elsevier, 2004: 144176.
［26］毛汉礼, 甘子均, 蓝淑芳. 长江冲淡水及其混合问题的初步探讨［J］. 海洋与湖沼, 1963, 5(3): 184205.
MAO Hanli, GAN Zijun, LAN Shufang. A preliminary study of the Yangtze diluted water and its mixing processes ［J］. Oceanologia Et Limnologia Sinica, 1963, 5(3): 184205.
［27］沈焕庭, 潘定安. 长江河口潮流特性及其对河床演变的影响［J］. 上海师范大学学报:自然科学版, 1979(2): 131144.
SHEN Huanting, PAN Dingan. The characteristics of tidal current and its effects on the channel changes of the Yangtze estuary ［J］. Journal of Shanghai Normal Univeristy: Natural Science, 1979(2): 131144.
［28］Shen H T, Hu H, Cannon G A, et al. Flow and mixing in the mouth of the Changjiang Estuary ［C］//Proceedings of the International Symposium on Sedimentation on the Continental Shelf with Special Reference to the East China Sea. Beijing:China Ocean Press, 1983: 148148.
［29］Hansen D V, Rattray M Jr. New dimensions in estuary classification ［J］. Limnology and Oceanography, 1966, 11: 319326.
［30］李身铎. 长江口潮流的垂直结构［J］. 海洋与湖沼, 1985, 16(4): 261273.
LI Shenduo. On the vertical structure of tidal currents in shallow water near the Changjiang river estuary ［J］. Oceanologia Et Limnologia Sinica, 1985, 16 (4): 261273.
［31］Le K T. A preliminary study of the basic hydrographic features and the current structures off the Changjiang River mouth in the dry season ［J］. Progress in Oceanography, 1988, 21(34): 387400.
［32］张重乐, 沈焕庭. 长江口咸淡水混合及其对悬沙的影响［J］. 华东师范大学学报:自然科学报, 1988(4): 8388.
ZHANG Chongle, SHEN Huanting. Mixing of salt and fresh water in the Changjiang estuary and its effects on suspended sediment ［J］. Journal of East China Normal University：Natural Science, 1988(4): 8388.
［33］Shen H T, Zhang C L. Mixing of salt water and fresh water in the Changjiang River estuary and its effects on suspended sediment ［J］. Chinese Geographical Science, 1992, 2(4): 373381.
［34］朱建荣, 丁平兴, 胡敦欣. 2000年8月长江口外海区冲淡水和羽状锋的观测［J］.海洋与湖沼, 2003, 34 (3): 249255.
ZHU Jianrong, DING Pingxing, HU Dunxin. Observation of the diluted water and plume front off the Changjiang river estuary during August 2000 ［J］. Oceanologia Et Limnologia Sinica, 2003, 34(3): 249255.
［35］Zhu J R, Wang J H, Shen H T, et al. Observation and analysis of the diluted water and red tide in the sea off the Changjiang River mouth in middle and late June 2003 ［J］. Chinese Science Bulletin, 2005, 50 (3): 18.
［36］孔亚珍, 丁平兴, 贺松林. 长江口邻近海域余流的基本特征分析［J］. 海洋科学进展, 2007, 25(4): 367375.
KONG Yazhen, DING Pingxing, HE Songlin. Analysis of basic characteristics of residual current in the Changjiang river estuary and adjacent sea areas ［J］. Advances in Marine Science, 2007, 25(4): 367375.
［37］于东生, 田淳, 严以新. 长江口水流运动特性分析［J］. 水运工程, 2004(1): 4953.
YU Dongsheng, TIAN Chun, YAN Yixin. An analysis of current characteristics at the Yangtze river estuary ［J］. Port & Waterway Engineering, 2004(1): 4953.
［38］刘志宇, 魏皓. 黄海潮流底边界层内湍动能耗散率与底应力的估计［J］. 自然科学进展, 2007, 17(3): 362369.
LIU Zhiyu, WEI Hao. Estimation of turbulent kinetic energy dissipation rate and bottom stress in the tidal flow boundary layer of Yellow sea ［J］. Progress in Natural Science, 2007, 17(3): 362369.
［39］Liu Z Y, Wei H, Lozovatsky I D, et al. Late summer stratification, internal waves, and turbulence in the Yellow Sea ［J］. Journal of Marine Systems, 2009, 77: 459472.
［40］许全喜. 三峡水库蓄水以来水库淤积和坝下冲刷研究［J］.人民长江， 2012: 43（7）： 16.
XU Quanxi. Research on reservoir sedimentation and downstream channel erosion of clam after impoundment of Three Gorges Reservair［J］. Yangtze River, 2012, 43(7): 16.
［41］范东华, 堪业良. 声学多普勒流速仪(ADCP)“旁辨”区数据处理方法的探讨［J］. 水道港口, 2006, 27: 3942.
FAN Donghua, KAN Yeliang. Discussion on data processing method in sidelooking zone using Acoustic Doppler Current Profiler ［J］. Journal of Waterway and Harbour, 2006, 27: 3942.
［42］Lawson K, Larson N G. CTD ［J］. Encyclopedia of Ocean Sciences, 2001(1): 579588.
［43］田淳, 刘少华.声学多普勒测流原理及其应用［M］. 郑州：黄河水利出版社， 2003: 5354.
［44］Pond S, Pickard G L. Introductory dynamical oceanography ［M］. 2nd ed. UK: ButterworthHeinemann, 1983.
［45］Millero F J, Poisson A. International oneatmosphere equation of state for seawater ［J］. DeepSea Research, 1981, 28A: 625629.
［46］Bigg P H, Density of water in SI units over the range 0-40℃［J］. British Journal of Applied Physics, 1967, 18: 521525.
［47］Thorpe S A. An introduction to ocean turbulence ［M］. Bangor: Cambridge University Press, 2007.
［48］Tritton D J. Physical fluid dynamics ［M］. 2nd ed. Oxford: Clarendon Press, 1988.
［49］Richardson L F. The criteria of atmosphere turbulence ［J］. Quarterly Journal of the Royal Meteorological Science, 1952, 78(33): 422425.
［50］Dyer K R. Estuaries: A physical introduction ［M］. 2nd ed. Chichester: John Wiley & Sons, 1997.
［51］Miles J W. On the stability of heterogeneous shear flows ［J］. Journal of Fluid Mechanics, 1961, 10: 496508.
［52］Peters H, Bokhorst R. Microstructure observations of turbulent mixing in a partially mixed estuary ［J］. Journal of Physical Oceanography, 1999, 30: 12321244.
［53］Liu Z Y. Instability of baroclinic tidal flow in a stratified fjord ［J］. Journal of Physical Oceanography, 2010, 40: 139154.
［54］Munk W H, Anderson E R. Notes on the theory of thermocline ［J］. Journal of Marine Research, 1948, 7: 276295.
［55］朱建荣, 肖成猷, 沈焕庭. 夏季长江冲淡水扩展的数值模拟［J］. 海洋学报, 1998, 20(5): 1322.
ZHU Jianrong, XIAO Chengyou, SHEN Huanting. Numerical model simulation of expansion of Changjiang diluted water in summer ［J］. Acta Oceanologia Sinica, 1998, 20(5): 1322.
［56］朱建荣, 肖成猷, 沈焕庭, 等. 黄海冷水团对长江冲淡水扩展的影响［J］.海洋与湖沼, 1998b, 29(4): 389394.
ZHU Jianrong, XIAO Chengyou, SHEN Huanting, et al. The impact of the Yellow sea cold water mass on the expansion of the Changjiang diluted water ［J］. Oceanologia Et Limnologia Sinica, 1998b, 29 (4): 389394.
［57］朱首贤, 朱建荣, 沙文钰. M2分潮对夏季长江冲淡水扩展影响的数值研究［J］. 海洋与湖沼, 1999, 30(6): 711718.
ZHU Shouxian, ZHU Jianrong, SHA Wenyu. A numerical study on the impact of M2 tide on the expansion of the Changjiang river diluted water in summer ［J］. Oceanologia Et Limnologia Sinica, 1999, 30 (6): 711718.
［58］Lu L F, Shi J Z. The dispersal processes within the tidemodulated Changjiang River plume, China ［J］. International Journal for Numerical Methods in Fluids, 2007, 55(12): 11431155.
［59］Shi J Z, Lu L F, Liu Y N. The hydrodynamics of an idealized estuarine plume along a straight coast: A numerical study ［J］. Environmental Modeling & Assessment, 2010, 15(6): 487502.
［60］Shi J Z, Lu L F. A short note on the dispersion, mixing, stratification and circulation within the plume of the partiallymixed Changjiang River estuary, China ［J］. Journal of HydroEnvironment Research, 2011, 5(2): 111126.