Diagnosing Coherent Structures in the Convective Boundary Layer by Optimizing Their Vertical Turbulent Scalar Transfer
Diagnosing Coherent Structures in the Convective Boundary Layer by Optimizing Their Vertical Turbulent Scalar Transfer
复制标题
通过优化垂直湍流标量传递来诊断对流边界层中的相干结构
DOI：
10.1007/s10546-019-00480-1
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发表时间：
2019
影响因子：
4.3
通讯作者：
Efstathiou G
中科院分区：
文献类型：
--
作者：
Efstathiou G
本文介绍了一种新的识别对流边界层相干结构的方法，该方法是通过优化大涡模拟所模拟的双流体湍流运动的垂直标量通量来实现的。新方法通过最大化由流体2和流体1中的平均性质决定的标量通量的一部分，将垂直速度和传输标量的联合频率分布(JFD)划分为相干结构(流体2)及其环境(流体1)。该方法不依赖于任何关于流动划分的先验准则，也不依赖于任何关于JFD形状的先验假设。基于最大化总的(流体1流体2)或流体2分辨的标量通量，以及是否考虑所有可能的分区或仅考虑一个子集，检验了不同风格的优化方法。这些选项可以导致相干结构的不同导出面积分数。将优化方法诊断出的相干结构的特性与表面发射衰变示踪剂的条件采样进行了比较，其中相干结构被定义为示踪剂扰动大于某一高度相关的阈值。结果表明，该优化方法能够平滑地确定水平方向和垂直方向上的相干热结构。此外，用流体-2分辨通量优化湍流传输产生了与示踪剂阈值方法非常相似的相干结构，特别是在它们的面积分数和上升气流速度方面。尽管如此，对JFD划分的进一步分析表明，尽管相干结构的面积分数可能相似，但它们的定义可以占据JFD的不同象限，这意味着不同的物理机制对边界层中的湍流传输的贡献。最后，根据相干结构的定义标准，研究了相干结构的运动学和热力学特性。
A new method is introduced to identify coherent structures in the convective boundary layer, based on optimizing the vertical scalar flux in a two-fluid representation of turbulent motions as simulated by a large-eddy simulation. The new approach partitions the joint frequency distribution (JFD) of the vertical velocity and a transported scalar into coherent structures (fluid 2) and their environment (fluid 1) by maximizing that part of the scalar flux resolved by the mean properties in fluid 2 and fluid 1. The proposed method does not rely on any a priori criteria for the partitioning of the flow nor any pre-assumptions about the shape of the JFD. Different flavours of the optimization approach are examined based on maximizing either the total (fluid 1fluid 2) or the fluid-2 resolved scalar flux, and on whether all possible partitions or only a subset are considered. These options can result in different derived area fractions for the coherent structures. The properties of coherent structures diagnosed by the optimization method are compared to the conditional sampling of a surface-emitted decaying tracer, in which coherent structures are defined as having tracer perturbation greater than some height-dependent threshold. Results show that the optimization method is able to smoothly define coherent thermal structures in both the horizontal and the vertical. Moreover, optimizing the turbulent transfer by the fluid-2 resolved flux produces very similar coherent structures to the tracer threshold method, especially in terms of their area fraction and updraft velocities. Nonetheless, further analysis of the partitioning of the JFD reveals that, even though the area fraction of coherent structures might be similar, their definition can occupy different quadrants of the JFD, implying the contribution of different physical mechanisms to the turbulent transfer in the boundary layer. Finally, the kinematic and thermodynamic characteristics of the coherent structures are examined based on their definition criteria.
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影响因子：
4.3
作者：
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DOI：
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期刊：
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DOI：
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发表时间：
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期刊：
Journal of Applied Meteorology
影响因子：
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