Dimensionless criteria for the production‐dissipation equilibrium of scalar fluctuations and their implications for scalar similarity
Dimensionless criteria for the production‐dissipation equilibrium of scalar fluctuations and their implications for scalar similarity
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标量波动的产生耗散平衡的无量纲标准及其对标量相似性的影响
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发表时间：
2012
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通讯作者：
M. Chamecki
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作者：
D. M. Cancelli;N. Dias;M. Chamecki
在水资源中，通常认为两个标量在大气表层具有相似的行为。这是莫宁-奥布霍夫相似性理论的一个推论，其直接含义是两个标量之间的所有相似函数都是相等的。然而，许多工作表明，标量相似性并不总是保持在不稳定的条件下，这一事实往往是很难建立一个物理原因。在本文中，使用的数据集在冬季在巴西的热带湖泊（Furnas湖），我们发现温度-水汽相似性和表面强迫的强度之间的关系，我们还证实了经典的平衡梯度生产和分子耗散的标量方差和协方差是标量相似性的关键。这种平衡可能被三阶输运项的大值破坏，也可能被非平稳项破坏。与标量方差和协方差预算有关，我们提出了一组新的无量纲标量通量数，它们能够很好地诊断每个预算的上述平衡（或缺乏平衡）。事实上，不同的Monin-Obukhov函数并不同样能够识别标量相似性，并提出了一个新的标量通量相似性的整体指标，其绝对值，不像相对传输效率，是由1以上的限制;这个新的指标也适用于谱域。最后，我们验证了低频相异度对标量相似性的影响大于标量通量相似性。
In water resources it is common to consider that two scalars have a similar behavior in the atmospheric surface layer. This is a consequence of Monin‐Obukhov similarity theory whose direct implication is that all similarity functions between two scalars are equal. However, many works show that scalar similarity does not always hold under unstable conditions, a fact for which it is often difficult to establish a physical cause. In this paper, using a data set measured during winter over a tropical lake in Brazil (Furnas Lake), we found a relation between temperature–water vapor similarity and the strength of the surface forcing; we also confirmed that the classical balance between gradient production and molecular dissipation of scalar variance and covariance is key to scalar similarity. This balance can be disrupted by large values of the third‐order transport terms, and possibly by nonstationary terms as well. In connection with the scalar variance and covariance budgets, we propose a new set of dimensionless scalar flux numbers which are able to make a good diagnosis of the aforementioned balance (or the lack thereof) for each budget. The fact that different Monin‐Obukhov functions are not equally capable of identifying scalar similarity is also demonstrated and a new bulk indicator of scalar flux similarity is proposed whose absolute value, unlike the relative transfer efficiency, is bounded above by 1; this new indicator holds also in the spectral domain. Finally, we verify that low‐frequency dissimilarity has a larger impact over scalar similarity than over scalar flux similarity.