A diapycnal diffusivity model for stratified environmental flows
A diapycnal diffusivity model for stratified environmental flows
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DOI：
10.1016/j.dynatmoce.2013.02.002
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发表时间：
2013-06-01
影响因子：
1.7
通讯作者：
Boegman, Leon
中科院分区：
文献类型：
--
作者：
Bouffard, Damien;Boegman, Leon
密度的垂直扩散系数K-rho调节着海洋环流、气候和沿海水质。在这些分层湍流中，K-rho很难测量和建模，因此需要从更容易测量的流量中发展K-rho参数化。通常，K-rho是用Osborn- cox模型从湍流温度波动参数化的，或者用Osborn模型从浮力频率N、运动粘度nu和湍流动能耗散率epsilon参数化的。最近，Shih等人（2005，J.流体力学，525:193-214）提出了一个实验室尺度参数化K-rho，在普朗特数（粘度与分子扩散率之比）Pr = 0.7时，湍流强度参数Re-b = epsilon/(nu N-2)，这是湍流的不稳定效应与分层和粘度的稳定效应之间的比率。在本研究中，我们扩展了SKIP参数化，针对广泛的已发表数据集，超过0.7 < Pr < 700，并在野外尺度上验证了它。我们的研究结果表明，必须对SKIF模型进行修改，以包括一个新的浮力控制的混合体系，在分子和过渡体系之间，其中K-rho分别使用分子扩散率和Osborn模型来捕获。浮力控制状态发生在10(2/3)Pr(-1/2) < Re-b < (3ln根Pr)(2)，其中K-rho = 0.1/Pr-1/4 nu Re-b（3/2）与Pr相关。这一范围被证明是湖泊和海洋的特征，Osborn和Osborn- cox模式系统地低估了这一区域的K-rho。(C) 2013 Elsevier B.V.版权所有
The vertical diffusivity of density, K-rho, regulates ocean circulation, climate and coastal water quality. K-rho is difficult to measure and model in these stratified turbulent flows, resulting in the need for the development of K-rho parameterizations from more readily measurable flow quantities. Typically, K-rho is parameterized from turbulent temperature fluctuations using the Osborn-Cox model or from the buoyancy frequency, N, kinematic viscosity, nu, and the rate of dissipation of turbulent kinetic energy, epsilon, using the Osborn model. More recently, Shih et al. (2005, J. Fluid Mech. 525: 193-214) proposed a laboratory scale parameterization for K-rho, at Prandtl number (ratio of the viscosity over the molecular diffusivity) Pr = 0.7, in terms of the turbulence intensity parameter, Re-b = epsilon/(nu N-2), which is the ratio between the destabilizing effect of turbulence to the stabilizing effects of stratification and viscosity. In the present study, we extend the SKIP parameterization, against extensive sets of published data, over 0.7 < Pr < 700 and validate it at field scale. Our results show that the SKIF model must be modified to include a new Buoyancy-controlled mixing regime, between the Molecular and Transitional regimes, where K-rho is captured using the molecular diffusivity and Osborn model, respectively. The Buoyancy-controlled regime occurs over 10(2/3)Pr(-1/2) < Re-b < (3 ln root Pr)(2), where K-rho = 0.1/Pr-1/4 nu Re-b(3/2) is Pr dependent. This range is shown to be characteristic to lakes and oceans and both the Osborn and Osborn-Cox models systematically underestimate K-rho in this regime. (C) 2013 Elsevier B.V. All rights reserved.