Observations of submeso motions and intermittent turbulent mixing across a low level jet with a 132‐m tower
Observations of submeso motions and intermittent turbulent mixing across a low level jet with a 132‐m tower
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DOI：
10.1002/qj.3192
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发表时间：
2018
影响因子：
8.9
通讯作者：
L. Mortarini;D. Cava;U. Giostra;Otávio C. Acevedo;L. G. N. Martins;P. Oliveira;Domenico Anfossi
中科院分区：
文献类型：
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作者：
L. Mortarini;D. Cava;U. Giostra;Otávio C. Acevedo;L. G. N. Martins;P. Oliveira;Domenico Anfossi
本文研究了夜间稳定边界层中波浪状亚中尺度运动和各向异性间歇湍流的共存。不同特征和幅度的亚中尺度运动相互作用。这些相互作用可能导致间歇性湍流的产生，从而改变稳定边界层的湍流结构。另一方面，湍流的产生和传递影响亚中尺度运动的微妙平衡。在这项工作中，声波风速计数据收集在11个级别在巴西东南部已被用来研究一个案例的夜间边界层在沿海地区。天气尺度强迫的缺失使得微风环流得以发展，在微风环流上产生中等强度（4 m s−1）和低高度（约50 m）的低空急流。急流的发展与脏波相耦合，而急流的充分发展则与强烈的垂直温度梯度驱动的重力波相关联。以低空急流鼻为中心的层具有水平弯曲和非常弱的湍流强度的特征。低空急流最大值以下和以上的空气经历湍流强度显著增加的爆发，显示出三层结构。水平风分量的振荡表现出与温度振荡相同的频率，这表明存在足够的温度水平梯度是曲折现象的基本驱动因素之一。通过欧拉自相关函数检测弯曲时间及其振荡时间尺度，并通过连续Morlet小波函数检测重力波及其空间时间尺度和时间演化的特征，研究了所考虑的夜晚。
The coexistence of wave‐like submeso motions and anisotropic intermittent turbulence in a night‐time stable boundary layer is investigated. Submeso motions of different characteristics and amplitudes interact with each other. These interactions may lead to intermittent turbulence production which alters the turbulent structure of the stable boundary layer. On the other hand, the production and transfer of turbulence affect the delicate balance of submeso motions. In this work, sonic anemometer data collected at 11 levels in southeastern Brazil have been used to study a case of a nocturnal boundary layer at a coastal site. The absence of forcing at the synoptic scale allows the development of a breeze circulation on which a low‐level jet of moderate intensity (4 m s−1) and low height (about 50 m) takes place. The jet evolution is coupled with dirty waves, while its full development is associated with gravity waves driven by a strong vertical temperature gradient. The layer centred at the low‐level jet nose is characterized by horizontal meandering and very weak turbulence intensity. The air far below and above the low‐level jet maximum experiences bursts of significant increase of the turbulence intensity, showing a three‐layer structure. The oscillations of the horizontal wind components exhibit the same frequency as the temperature oscillations, suggesting that the presence of an adequate temperature horizontal gradient is one of the fundamental drivers of the meandering phenomenon. The considered night has been studied by means of the Eulerian auto‐correlation functions for the detection of the meandering hours and their oscillation time‐scales, and by means of the continuous Morlet wavelet function for the detection of the gravity waves and the characterization of their spatial time‐scales and temporal evolution.