Fine-scale turbulent bursts in stable atmospheric boundary layer in complex terrain
Fine-scale turbulent bursts in stable atmospheric boundary layer in complex terrain
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DOI：
10.1017/jfm.2017.717
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发表时间：
2016-06
影响因子：
3.7
通讯作者：
Eliezer Kit;C. Hocut;Dan Liberzon;Harindra J. S. Fernando
中科院分区：
文献类型：
--
作者：
Eliezer Kit;C. Hocut;Dan Liberzon;Harindra J. S. Fernando
大气边界层中的湍流通常是用声速风速仪(Sonic)测量的，但由于声速的空间分辨率(10$cm)和时间分辨率(32$HZ)较低，无法直接测量湍流动能耗散率等细尺度参数。相反，$\Unicode[stix]{x1D700}$是使用基于Kolmogorov理论的技术进行估计的。在山区地形大气模拟和观测(MATHORHON)计划的实地活动中，使用音速和热膜风速计DYAD(“组合”探测器)对ABL湍流进行了精细尺度的测量，精度可达Kolmogorov尺度。热膜探头位于音速探头体积内的万向节上，并自动在水平面上旋转，以与音速测量的平均流量对齐。该方法不仅满足了热膜与平均流量对准的要求，而且可以对热膜探头进行现场校准。本文分析了一段类似于分层平行切变流的夜间气流。组合探测器的测量显示了一个有趣的现象--强爆发的发生，其特征是速度起伏的短期增加和TKE耗散率的数量级增加。这些爆发表明，在更细(0.1美元-0.4m)尺度上的异常湍流活动是不被音速捕捉到的，因为后者所分辨的最小尺度大于0.6m。在爆发存在的情况下，光谱在中间到惯性和耗散子范围的尺度上表现出凸起，类似于瓶颈现象。它的表现，虽然明确地与爆发有关，但可能不能令人信服地符合先前的瓶颈效应理论的框架，这些理论暗示粘性效应或浮力效应通过非局部效应改变局部能量级联。爆炸的起源尚不清楚。具有突发性的分层ABL表现出非Kolmogorov行为，因此应谨慎建模。
Turbulence in the atmospheric boundary layer (ABL) is usually measured using sonic anemometers (sonics), but coarse spatial ( ${\sim}10$ cm) and temporal ( ${\sim}32$ Hz) resolutions of sonics preclude direct measurement of fine-scale parameters such as the turbulent kinetic energy (TKE) dissipation rate $\unicode[STIX]{x1D700}$ . Instead, $\unicode[STIX]{x1D700}$ is estimated using techniques based on Kolmogorov theory. Fine-scale measurements of ABL turbulence down to Kolmogorov scale were made with a sonic and hot-film anemometer dyad (a ‘combo’ probe) during the field campaigns of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) programme. The hot-film probe was located on a gimbal within the sonic probe volume, and was automated to rotate in the horizontal plane to align with the mean flow measured by sonic. This procedure not only helped satisfy the requirement of hot-film alignment with the mean flow, but also allowed in situ calibration of hot-film probes. This paper analyses a period of nocturnal flow that was similar to a stratified parallel shear flow. The combo-probe measurements showed an interesting phenomenon – the occurrence of strong bursts, characterized by short-term increase of velocity fluctuations and simultaneous increase of TKE dissipation rate by orders of magnitude. These bursts were indicative of unusual turbulence activity at finer ( ${\sim}0.1$ –0.4 m) scales that are not captured by sonics since the smallest scales resolved by the latter are greater than 0.6 m. With bursting present, the spectra exhibited bumps at scales intermediate to inertial and dissipation subranges, resembling a bottleneck phenomenon. Its manifestation, although unequivocally related to bursts, may not convincingly fit into the framework of previous bottleneck-effect theories that allude to either viscous effects or buoyancy effects modifying the local energy cascade via non-local effects. The origins of burst are yet to be identified. Stratified ABL with bursts exhibits non-Kolmogorov behaviour, and hence should be modelled with caution.