COLLABORATIVE RESEARCH: The Role of Canopy Structure on Variability of Water and Heat Fluxes from Forested Watersheds

本文研究了森林流域和大气边界层（ABL）之间的水汽、能量和动量交换，结合了新兴的湍流数值模拟工具和最近一次综合野外活动的结果。在1997年10月进行的实地实验中，七个研究小组在北卡罗莱纳州达勒姆附近杜克森林松树林中的七座塔上测量了陆地表面水蒸气、热量、二氧化碳和动量的通量。这里研究的数据集是第一个综合实验，包括在森林的冠层亚层中多达七个地点同时进行速度统计和通量测量，以及空间上详细的叶面积密度剖面测量。为了探索和推广森林结构与观测到的热、水汽通量之间的关系，提出了三维大涡模拟（LES）的研究方法。这些模拟首次明确考虑了叶面积密度在空间上的变异性，并采用辐射传输方案来真实地解释叶元素的能量衰减。模拟将树叶视为一个多重连接的多孔介质，将允许研究森林冠层的空间结构如何与能量/辐射和湍流传输动力学相互作用，从而产生观测到的冠层内部和上方陆地表面通量场的空间格局。预期的结果是了解在冠层亚层内通量测量中，通量的空间变异性可归因于冠层结构的空间变异性。这项研究的结果将指导未来的野外实验，这些实验试图通过塔式测量来估计全森林的平均通量，并将严格评估一维冠层模型的适用范围。

9903471 KatulThis study investigates the exchange of water vapor, energy, and momentum between forested watersheds and the atmospheric boundary layer (ABL), using a combination of emerging tools in numerical simulation of turbulent flow and transport through and above plant canopies and recent result from a comprehensive field campaign. The field experiment, conducted in October of 1997, included seven research groups measuring land surface fluxes of water vapor, heat, carbon dioxide, and momentum on seven towers situated within a pine forest at Duke Forest near Durham, North Carolina. The data set studied here is the first comprehensive experiment that includes simultaneous velocity statistics and flux measurements at as many as seven locations in the canopy sublayer of a forest along with detailed leaf area density profile measurements in space. To explore and generalize the relationship between forest structure and observed heat and water vapor fluxes, an investigation using three-dimensional Large Eddy Simulations (LES) is proposed. These simulations are the first to explicitly consider variability in leaf area density in space and employ radiative transfer schemes to realistically account for energy attenuation by foliage elements. The simulations, which treat the foliage as a multiply-connected porous medium, will permit investigating how the spatial structure of forest canopies interact with energy/radiation and the turbulent transport dynamics to give rise to the observed spatial patterns in land surface flux fields within and above the canopy. An anticipated result is an understanding of what spatial variability in fluxes could be attributed to spatial variability in canopy structure for flux measurements within the canopy sublayer. The results from this study will guide future field experiments that seek to estimate forest-wide average fluxes from tower measurement and will rigorously assess the range of applicability of one-dimensional canopy models.