The boundary condition for vertical velocity and its interdependence with surface gas exchange
The boundary condition for vertical velocity and its interdependence with surface gas exchange
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垂直速度的边界条件及其与表面气体交换的相互依赖性
DOI：
10.5194/acp-17-8177-2017
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发表时间：
2017
影响因子：
6.3
通讯作者：
A. Kowalski
中科院分区：
文献类型：
--
作者：
A. Kowalski
抽象的。线动量守恒定律适用于地面气体交换，采用尺度分析来诊断边界层中的垂直速度（w）。地面层中的净向上动量是由蒸发（E）强迫的，并定义了非零的垂直运动，其大小由E与空气密度之比定义，即w = E/ρ。这是真的，甚至在表面上，边界条件是w| 0 = E/ρ| 0（其中w| 0和ρ| 0代表地面空气的垂直速度和密度）。这种斯特凡流速意味着向上传输的非扩散性质，这是对流层的一般特征，但特别重要的是在表面，它有助于分子扩散与向上的气体迁移（例如H2O），但反对向下扩散的物种，如CO2在白天。通量梯度关系（涡流扩散率）的定义需要整流，以排除不依赖于标量梯度的非扩散输运。在微观尺度上，非扩散性运输在蒸发过程中的作用，从一个狭窄的管道内-与蒸汽运输到一个覆盖，水平气流-很久以前在经典力学中描述，并经常占化学工程师，但一直被忽视的科学家研究气孔导度。正确地解释通过气孔的非扩散性运输，可以明显减少净CO2运输，并略微增加水蒸气的运输，应该改善生态系统和植物功能的特性。
Abstract. The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E/ρ . This is true even right down at the surface where the boundary condition is w|0 = E/ρ|0 (where w|0 and ρ|0 represent the vertical velocity and density of air at the surface). This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, for example) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux–gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal airstream – was described long ago in classical mechanics and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterisations of ecosystem and plant functioning.
影响因子：
5.2
作者：
Beer, C.;Ciais, P.;Wohlfahrt, G.
通讯作者：
Wohlfahrt, G.