A Study of Spectra, Structure and Correlation Functions and Their Implications for the Stationarity of Surface-Layer Turbulence
A Study of Spectra, Structure and Correlation Functions and Their Implications for the Stationarity of Surface-Layer Turbulence
复制标题
谱、结构和相关函数的研究及其对表层湍流平稳性的影响
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
C. M. P. Okawa
中科院分区：
文献类型：
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作者：
N. Dias;M. Chamecki;Akemi Kan;C. M. P. Okawa
在Monin-Obukhov相似理论的框架内，平稳性和积分时间尺度的存在和值的相关概念是分析微气象数据的能力的核心。该理论不仅强烈地依赖于平稳性假设，而且湍流矩的估计及其精度取决于相应的积分时间标度的值。尽管这些概念总体上很重要，但与它们相关的研究相对较少。此外，虽然每个湍流变量都有它自己的积分尺度，但在估计数值时往往忽略了这一事实。在这项工作中，我们研究了三个地表逆温形成的白天事件，即明显存在非平稳周期的事件。我们的分析揭示了温度数据中的低频成分并没有被简单的(但在湍流数据分析中经常使用)一阶递归滤波完全去除，必须在频域中过滤掉这个成分，然后才能恢复温度和湿度统计描述符(在这种情况下是结构函数)之间的相似性。在应用一个简单的准则来估计积分时间尺度的数值之后，我们能够估计积分尺度的存在与相应过程的平稳性之间的关系。最后，我们发现在二阶矩的情况下，萨曼诺夫定理并不总是适用的。然后简要讨论了对这些分量的精度估计的影响。
The related concepts of stationarity and the existence and values of integral timescales are central to the ability of analyzing micrometeorological data within theframework of Monin–Obukhov similarity theory. Not only does the theory strongly hinge on the stationarity assumption, the estimation of turbulence moments and their accuracies are dependent on the values of the correspondent integral time scales. In spite of the general importance of these concepts, there are relatively few studiesconcerned with them. Moreover, although each turbulence variable has its ownintegral scale, this fact is often overlooked when numerical values are estimated.In this work we study three daytime events of surface inversion formation, that is,events where a nonstationary period is clearly present. Our analysis reveals alow-frequency component in the temperature data that is not totally removed bya simple (but often used in turbulence data analysis) first-order recursive filter.This component has to be filtered out in the frequency domain, after which we areable to recover similarity between temperature and humidity statistical descriptors(in this case, the structure function). After applying a simple criterion to estimatenumerical values of the integral time scales, we are able to assess the relationshipsbetween the existence of integral scales and the stationarity of the correspondingprocess. Finally, we find out that in the case of second-order moments the Sarmanovtheorem does not always apply. The implications for accuracy estimates of thesemoments are then briefly discussed.