Realistic forests and the modeling of forest-atmosphere exchange
Realistic forests and the modeling of forest-atmosphere exchange
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DOI：
10.1002/essoar.10506854.1
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
E. Bannister;A. R. MacKenzie;Xiaoming Cai
中科院分区：
文献类型：
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作者：
E. Bannister;A. R. MacKenzie;Xiaoming Cai
森林覆盖了地球近三分之一的陆地面积，并与大气交换质量、动量和能量。对这些交换的大多数研究，特别是使用数字模型，都认为森林的结构已经大大简化。在许多景观中，这些简化是不现实的。不均匀的地形和不稳定的天气条件产生了流体动力学特征，导致观测被不准确地解释、偏见或过度概括。在第一部分中，我们讨论了在理解现实森林上的湍流交换方面的实验、理论和数值进展。在现实环境中，标量输送不一定跟随水流，这意味着在斑驳的森林周围标量很少达到平衡，并且在森林丘陵的背风处可能形成显著的标量通量。缝隙和斑块会产生巨大的空间通量，而目前的模型和观测都忽略了这一点。大气不稳定增加了森林边缘通量调节的距离。在落叶林中，斑块的影响因季节而异；与直觉相反的是，旋涡深入到树叶茂盛的树冠(因为它们在空气动力学上更粗糙)。空气包裹在斑块状森林中的停留时间可能比同质森林要短得多，特别是在边缘附近。在第二部分中，我们提出了使森林-大气数值模式更加逼真的实用方法，包括考虑重新配置和真实的冠层结构，并开始在湍流解析模式中包括更多的化学和物理过程。未来的挑战包括：(A)根据实际研究地点定制数值模型，(B)将空间和时间尺度连接起来，(C)在数值模型中纳入更大范围的天气条件。
Forests cover nearly a third of the Earth's land area and exchange mass, momentum, and energy with the atmosphere. Most studies of these exchanges, particularly using numerical models, consider forests whose structure has been heavily simplified. In many landscapes, these simplifications are unrealistic. Inhomogeneous landscapes and unsteady weather conditions generate fluid dynamical features that cause observations to be inaccurately interpreted, biased, or over‐generalized. In Part I, we discuss experimental, theoretical, and numerical progress in the understanding of turbulent exchange over realistic forests. Scalar transport does not necessarily follow the flow in realistic settings, meaning scalar quantities are rarely at equilibrium around patchy forests, and significant scalar fluxes may form in the lee of forested hills. Gaps and patchiness generate significant spatial fluxes that current models and observations neglect. Atmospheric instability increases the distance over which fluxes adjust at forest edges. In deciduous forests, the effects of patchiness differ between seasons; counter intuitively, eddies reach further into leafy canopies (because they are rougher aerodynamically). Air parcel residence times are likely much lower in patchy forests than homogeneous ones, especially around edges. In Part II, we set out practical ways to make numerical models of forest‐atmosphere more realistic, including by accounting for reconfiguration and realistic canopy structure and beginning to include more chemical and physical processes in turbulence resolving models. Future challenges include: (a) customizing numerical models to real study sites, (b) connecting space and time scales, and (c) incorporating a greater range of weather conditions in numerical models.