长江口外羽状流水体中的垂向混合与层化的观测与分析  

Measurement and Analysis of Vertical Mixing and Stratification Within the Plume Outside the Changjiang River Estuary

作　　者：倪智慧[1] 陈辉[1] 董礼先[2] 时钟[1] 王殿志[1] 翟强[1] 

机构地区：[1]上海交通大学港口与海岸工程系,上海200030 [2]国家海洋局第二海洋研究所,杭州310012

出　　处：《上海交通大学学报》2012年第11期1862-1873,共12页Journal of Shanghai Jiaotong University

基　　金：国家自然科学基金(50679040);上海交通大学特聘教授基金(DP2009012);海洋工程国家重点实验室自主研究课题(GKZD010056-9)资助项目

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300kHz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-0.36～0.61m/s,南北向流速大小范围为-0.59～0.39m/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.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 equa tions available in the literature, density, buoyancy frequency and the gradient Richardson number were es timated 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）. Ver- tical profiles of velocity components, salinity, temperature, density, buoyancy frequency and the gradientRichardson 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

关 键 词：长江口外 羽状流 浮力频率 梯度Richardson数 混合 层化 

分 类 号：P731.26[天文地球—海洋科学]