On the relationship between the eddy covariance, the turbulent flux, and surface exchange for a trace gas such as CO2
On the relationship between the eddy covariance, the turbulent flux, and surface exchange for a trace gas such as CO2
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DOI：
10.1007/s10546-007-9171-z
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发表时间：
2007-08-01
影响因子：
4.3
通讯作者：
Serrano-Ortiz, Penelope
中科院分区：
文献类型：
--
作者：
Kowalski, Andrew S.;Serrano-Ortiz, Penelope
在 CO2 表面交换估计的背景下，结合扩散和标量守恒基本原理的分析表明，混合比是定义（涡流协方差）湍流通量以及表达边界层预算方程中湍流通量和表面交换之间关系的适当变量。有时选择的其他标量强度变量，即二氧化碳密度和摩尔分数，容易受到热量和水蒸气表面交换的影响。对塔测量高度以下的边界层“控制体积”应用测高分析揭示了先前应用方法的缺陷：(a) 不能假设不可压缩性来简化质量守恒（以二氧化碳密度表示的预算）； (b) 压缩性本身就使得质量守恒分析容易受到与所得非零垂直速度相关的不确定性的影响，该速度太小而无法在真实地形上进行测量或建模； (c) WPL（Webb 等人（1980）Quart J Roy Meteorol Soc 106：85-100）“零干燥空气通量”假设无效，除了表面边界外。然而，WPL 项的定义和删除并不取决于最后一个假设，因此可以使用开路或闭路设计的气体分析仪通过涡流协方差准确确定湍流 CO2 通量。附录讨论了推导 WPL 术语所需的假设和适当的解释。
In the context of CO2 surface exchange estimation, an analysis combining the basic principles of diffusion and scalar conservation shows that the mixing ratio is the appropriate variable both for defining the (eddy covariance) turbulent flux and also for expressing the relationship between the turbulent flux and surface exchange in boundary-layer budget equations. Other scalar intensity variables sometimes chosen, both the CO2 density and molar fraction, are susceptible to the influence of surface exchange of heat and water vapour. The application of a hypsometric analysis to the boundary-layer "control volume" below the tower measurement height reveals flaws in previously applied approaches: (a) incompressibility cannot be assumed to simplify mass conservation (the budget in terms of CO2 density); (b) compressibility alone makes the analysis of mass conservation vulnerable to uncertainties associated with resultant non-zero vertical velocities too small to measure or model over real terrain; and (c) the WPL (Webb et al. (1980) Quart J Roy Meteorol Soc 106:85-100) "zero dry air flux" assumption is invalidated except at the surface boundary. Nevertheless, the definition and removal of the WPL terms do not hinge upon this last assumption, and so the turbulent CO2 flux can be accurately determined by eddy covariance using gas analysers of either open- or closed-path design. An appendix discusses the necessary assumptions and appropriate interpretations for deriving the WPL terms.