The evolution of a stratified turbulent cloud
The evolution of a stratified turbulent cloud
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层状湍流云的演化
DOI：
10.1017/jfm.2013.612
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发表时间：
2013
影响因子：
3.7
通讯作者：
N. Swaminathan
中科院分区：
文献类型：
--
作者：
Andrea Maffioli;P. Davidson;S. Dalziel;N. Swaminathan
摘要本文研究的是分层流体中的局部湍流区或湍流云，它主要研究湍流区和周围静止区之间的边缘动力学。通过实验室实验和数值模拟的层状湍流云，我们确认，边缘动力学可以细分为物质驱动的入侵和水平传播的内部波包。三维可视化显示，内部重力波包实际上是大规模的煎饼结构，从湍流云生长到相邻的静止区域。对这些波包进行了时间跟踪，发现它们的速度服从线性重力内波的群速关系。能量的传播波，其中包括相对于水平倾斜的波形，也被认为是，它被发现，经过一段时间的两个涡流周转时间，内部重力波携带高达16%的云动能进入最初的静止区域。自然界中的湍流事件通常是以衰变湍流云的形式出现的，因此，从初始云辐射的内部重力波可能在大气和海洋中能量和动量的重组中发挥重要作用。
Abstract Localized regions of turbulence, or turbulent clouds, in a stratified fluid are the subject of this study, which focuses on the edge dynamics occurring between the turbulence and the surrounding quiescent region. Through laboratory experiments and numerical simulations of stratified turbulent clouds, we confirm that the edge dynamics can be subdivided into materially driven intrusions and horizontally travelling internal wave-packets. Three-dimensional visualizations show that the internal gravity wave-packets are in fact large-scale pancake structures that grow out of the turbulent cloud into the adjacent quiescent region. The wave-packets were tracked in time, and it is found that their speed obeys the group speed relation for linear internal gravity waves. The energetics of the propagating waves, which include waveforms that are inclined with respect to the horizontal, are also considered and it is found that, after a period of two eddy turnover times, the internal gravity waves carry up to 16 % of the cloud kinetic energy into the initially quiescent region. Turbulent events in nature are often in the form of decaying turbulent clouds, and it is therefore suggested that internal gravity waves radiated from an initial cloud could play a significant role in the reorganization of energy and momentum in the atmosphere and oceans.