夏季长江河口层化与湍流混合特征分析  

Summertime stratification and turbulent mixing in the Yangtze Estuary

作　　者：林姚坤 包芸[1] 陈起程 吴加学 LIN Yaokun;BAO Yun;CHEN Qicheng;WU Jiaxue(Department of Mechanics,Sun Yat-sen University,Guangzhou 510275,China;School of Marine Sciences,Sun Yat-sen University,Guangzhou 510275,China)

机构地区：[1]中山大学力学系,广东广州510275 [2]中山大学海洋科学学院,广东广州510275

出　　处：《热带海洋学报》2018年第5期33-39,共7页Journal of Tropical Oceanography

基　　金：国家重大科学研究计划全球气候变化研究专题(2013CB956502);国家自然科学基金面上项目(41576091)~~

摘　　要：利用2016年夏季长江河口现场水文特性与湍流微结构观测资料,分析了长江河口水体温盐结构、层化发育、湍流与混合特征。结果表明:1)夏季长江河口水体密度层化结构明显,根据各层水体密度梯度差异,可将水体分为底部混合层和上层密度跃层,两部分的密度层化界限与浮力频率等值线lgN^2=-4.0接近。2)底部混合层湍动能耗散率大,层化结构弱,水体分层稳定性弱;上层密度跃层湍动能耗散小,层化结构强,水体分层稳定性强,这有利于河口内波的发育与传播。3)在密度层化的作用下,水体的湍动能耗散率、湍动能剪切生成及浮力通量的能量关系在一定范围内符合湍动能局部能量平衡方程。不同层之间的湍流弗劳德数Fr_t和湍流雷诺数Ret在Fr_t-Re_t平面上呈现明显的分区,与经典的分层剪切流理论基本吻合。Hydrological and turbulent microstructural observations were conducted in summer 2016 to analyze the summertime stratification and turbulent mixing in the Yangtze Estuary.The temporal and spatial distributions of salinity,temperature,stratification,and turbulent mixing showed highly-stratified structures in the estuary.The vertical distributions of density vertical gradient in different layers demonstrated bottom mixed layer and upper pycnocline,where a division of the stratification was approximately along the contour line of lgN 2=?4.0.The bottom mixed layer had a stronger dissipation rate and unstably-stratified structure,while the upper pycnocline had a weaker dissipation rate and stably-stratified structure,where the formation and spread of internal waves would occur.Under the condition of stratified structure,the dissipation rate,turbulent shear production and buoyancy flux were found to satisfy the local turbulent kinetic energy balance.Turbulent Reynolds number Ret and turbulent Froude number Frt in the bottom mixed layer and the upper pycnocline were distributed in different regions of the Ret?Frt space,indicating that the stratification and mixing in the estuary was in line with the classical theory of Ivey and Imberger(1991).

关 键 词：分层流 浮力频率 底部混合层 上层密度跃层 长江河口 

分 类 号：P731.26[天文地球—海洋科学]