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Contrasting dynamic characteristics of shear turbulence and Langmuir circulation in the surface mixed layer
在上混合层内剪切湍流和朗缪尔环流的动力特征差异
Received:August 07, 2013  Revised:December 18, 2014
DOI:
Key words:Ocean surface mixed layer  South China Sea  Shear turbulence  Langmuir circulation  large eddy simulation
中文关键词:  海洋上混合层  南海  剪切湍流  朗缪尔环流  大涡模拟
基金项目:国家重点基础研究发展计划(973计划)
Author NameAffiliationAddress
Guojing LI State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 广东省广州市海珠区新港西路164号2号楼903A室
Dongxiao WANG* State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 510301
Yeqiang SHU State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 
Ju CHEN State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 
Jinglong YAO State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 
Dandan SUI State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,CAS 
Lili ZENG South China Sea Institute of Oceanology Chinese Academy of Sciences 
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Abstract:
      Large eddy simulation (LES) is used to investigate contrasting dynamic characteristics of shear turbulence (ST) and Langmuir circulation (LC) in the surface mixed layer (SML). ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downwelling jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 2~3 Stokes depth scale and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy (TKE) generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Km are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear (S2) near the SML base. In addition, the large-scale eddies and S2 induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.
中文摘要:
      采用大涡模拟模式探究了在南海上混合层中剪切湍流与朗缪尔环流的特征。风场和波浪场均沿着径向方向;波浪场为对应风速的稳定单色波。结果表明风诱导剪切湍流其最大的向下的速度为1.7cm/s。朗缪尔环流抑制了水平方向上的速度,特别是顺风方向的速度,但增加了向下的速度且最大向下的速度达到了3.8cm/s。朗缪尔环流诱导的强向下射流速度诱导了比剪切湍流更大的动量通量。朗缪尔环流诱导的涡粘和涡扩散系数要比剪切湍流大得多,朗缪尔环流诱导的涡粘与涡扩散系数的最大值位于斯托克斯深度尺度并逐渐振荡减小,但在垂直风速方向上的动量最大值的上部,涡粘与涡扩散系数突然增大而后逐渐减小。剪切湍流涡粘与涡扩散系数的最大值位于混合层的中部。朗缪尔环流诱导的湍动能在海表5m以下大于剪切湍流诱导的湍动能,大的湍动能能够诱导大的混合系数,但是湍动能和涡粘与涡扩散系数的形状差异巨大,因此在对朗缪尔环流进行参数化时不能仅依赖于湍动能。对于深的混合层,朗缪尔环流能够在混合层底部诱导强的剪切,并导致了朗缪尔环流诱导的标量通量要大于剪切湍流诱导的标量通量,所以在的参数化朗缪尔环流时需要充分考虑朗缪尔环流诱导的混合层底部的强剪切。
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