Multiscale Shear Forcing of Turbulence in the Nocturnal Boundary Layer: A Statistical Analysis
Multiscale Shear Forcing of Turbulence in the Nocturnal Boundary Layer: A Statistical Analysis
复制标题
夜间边界层湍流的多尺度剪切力：统计分析
DOI：
10.1007/s10546-020-00583-0
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发表时间：
2020
影响因子：
4.3
通讯作者：
N. Vercauteren
中科院分区：
文献类型：
--
作者：
V. Boyko;N. Vercauteren
夜间低层边界层是由间歇性湍流控制的，这被认为是由所谓的亚中尺度运动的零星活动以一种复杂的方式触发的。我们基于次平均尺度的垂直梯度与湍流动能之间的假设关系来分析间歇性湍流。我们分析了在雪面通量II现场计划期间从30米塔顶收集的高分辨率夜间涡旋相关资料。利用离散小波变换将非湍流速度信号分解为平均、喷流和亚中尺度三个尺度范围。次平均尺度的垂直梯度是用有限差分估计的。湍流动能被模拟为具有外生变量的离散时间自回归过程，其中外生变量是次平均尺度的垂直梯度。离散模式的参数随时间演化取决于局部主导的湍流产生尺度。用子空间聚类算法估计了模式参数平均后的三个区域，对于非常稳定的边界层，这三个区域在湍流和亚中尺度运动的能量相空间中呈弱双峰分布。一种模式表示由次中尺度运动调制的湍流。此外，如果次中尺度强度超过强层结平均动能的10%，将出现间歇性湍流。
The lower nocturnal boundary layer is governed by intermittent turbulence which is thought to be triggered by sporadic activity of so-called sub-mesoscale motions in a complex way. We analyze intermittent turbulence based on an assumed relation between the vertical gradients of the sub-mean scales and turbulence kinetic energy. We analyze high-resolution nocturnal eddy-correlation data from 30-m tower collected during the Fluxes over Snow Surfaces II field program. The non-turbulent velocity signal is decomposed using a discrete wavelet transform into three ranges of scales interpreted as the mean, jet and sub-mesoscales. The vertical gradients of the sub-mean scales are estimated using finite differences. The turbulence kinetic energy is modelled as a discrete-time autoregressive process with exogenous variables, where the latter ones are the vertical gradients of the sub-mean scales. The parameters of the discrete model evolve in time depending on the locally-dominant turbulence-production scales. The three regimes with averaged model parameters are estimated using a subspace-clustering algorithm which illustrates a weak bimodal distribution in the energy phase space of turbulence and sub-mesoscale motions for the very stable boundary layer. One mode indicates turbulence modulated by sub-mesoscale motions. Furthermore, intermittent turbulence appears if the sub-mesoscale intensity exceeds 10%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10 \%$$\end{document} of the mean kinetic energy in strong stratification.