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.

中文翻译：

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夜间边界层湍流的多尺度剪切强迫：统计分析

较低的夜间边界层由间歇性湍流控制，这被认为是由所谓的亚中尺度运动的零星活动以复杂的方式触发的。我们基于次均值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 Fluxes over Snow Surfaces II 现场计划期间收集的 30 米塔的高分辨率夜间涡相关数据。使用离散小波变换将非湍流速度信号分解为三个尺度范围，解释为均值、喷射和亚中尺度。使用有限差分来估计次均值尺度的垂直梯度。湍流动能被建模为具有外生变量的离散时间自回归过程，其中后者是次均值尺度的垂直梯度。离散模型的参数根据局部主导的湍流产生尺度随时间变化。使用子空间聚类算法估计具有平均模型参数的三个状态，该算法说明了非常稳定的边界层的湍流和亚中尺度运动的能量相空间中的弱双峰分布。一种模式表示由亚中尺度运动调制的湍流。此外，