Intermittent Turbulence Associated with a Density Current Passage in the Stable Boundary Layer
Intermittent Turbulence Associated with a Density Current Passage in the Stable Boundary Layer
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DOI：
10.1023/a:1019969131774
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发表时间：
2002-11
影响因子：
4.3
通讯作者：
Jielun Sun;S. Burns;D. Lenschow;R. Banta;R. Newsom;R. Coulter;S. Frasier;T. Ince;C. Nappo;J. Cuxart;W. Blumen;X. Lee;Xinzhang Hu
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文献类型：
--
作者：
Jielun Sun;S. Burns;D. Lenschow;R. Banta;R. Newsom;R. Coulter;S. Frasier;T. Ince;C. Nappo;J. Cuxart;W. Blumen;X. Lee;Xinzhang Hu
利用在合作大气-地面交换研究-99（CASES-99）期间部署的前所未有的观测能力，我们在1999年10月18日晚上发现了三个不同的湍流事件，每一个都与不同的现象有关：密度流、孤立波和来自低空急流的向下传播波。在本研究中，我们着重于第一个事件，密度流及其相关的间歇性湍流。当冷密度流通过CASES-99站点传播时，密度流上部的涡旋运动导致分层流的周期性翻转、局部热不稳定和湍流混合的向下扩散。异重流的传播引起了对流循环.随着密度流头部的下降运动导致强烈的层结，湍流急剧减少，风速突然增加。当风涌向地面传播时，剪切不稳定性产生向上扩散的湍流混合。我们详细地论证了与密度流动力学有关的局部热不稳定性和剪切不稳定性的高度和顺序是造成明显湍流的原因。
Using the unprecedented observational capabilities deployed duringthe Cooperative Atmosphere-Surface Exchange Study-99 (CASES-99),we found three distinct turbulence events on the night of 18October 1999, each of which was associated with differentphenomena: a density current, solitary waves, and downwardpropagating waves from a low-level jet. In this study, we focus onthe first event, the density current and its associatedintermittent turbulence. As the cold density current propagatedthrough the CASES-99 site, eddy motions in the upper part of thedensity current led to periodic overturning of the stratifiedflow, local thermal instability and a downward diffusion ofturbulent mixing. Propagation of the density current induced asecondary circulation. The descending motion following the head ofthe density current resulted in strong stratification, a sharpreduction in the turbulence, and a sudden increase in the windspeed. As the wind surge propagated toward the surface, shearinstability generated upward diffusion of turbulent mixing. Wedemonstrate in detail that the height and sequence of the localthermal and shear instabilities associated with the dynamics ofthe density current are responsible for the apparent intermittentturbulence.