Effects of Gentle Topography on Forest‐Atmosphere Gas Exchanges and Implications for Eddy‐Covariance Measurements
Effects of Gentle Topography on Forest‐Atmosphere Gas Exchanges and Implications for Eddy‐Covariance Measurements
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DOI：
10.1029/2020jd032581
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发表时间：
2020-06
期刊：
影响因子：
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通讯作者：
Bicheng Chen;M. Chamecki;G. Katul
中科院分区：
文献类型：
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作者：
Bicheng Chen;M. Chamecki;G. Katul
对森林上方基于塔的涡流协方差（EC）湍流通量测量的解释取决于三个关键假设：(1)流量统计的稳定性，(2)标量源或汇的平面均匀性，(3)流量统计的平面均匀性。大涡模拟（LESs）用于控制前两种模式，以探索第三种模式对理想和真实温和地形的破坏，例如亚马逊河流域的地形。在覆盖复杂地形的均匀森林中采用均匀分布的源进行LES运行，将标量湍流通量的空间格局与地形特征联系起来。结果表明，地形引起的流量特征对通量有很强的调制作用，包括大面积的负通量补偿“烟囱”区，其通量几乎比景观通量大一个数量级。显著的空间异质性至少持续到两个冠层高度，其中大多数涡动相关测量是在高大森林上方进行的。引入异质性指数来表征和对比不同的情景，并表明地形分类在确定负通量和增强通量区域方面具有预测能力。
The interpretation of tower‐based eddy‐covariance (EC) turbulent flux measurements above forests hinges on three key assumptions: (1) steadiness in the flow statistics, (2) planar homogeneity of scalar sources or sinks, and (3) planar homogeneity in the flow statistics. Large eddy simulations (LESs) were used to control the first two so as to explore the break‐down of the third for idealized and real gentle topography such as those encountered in Amazonia. The LES runs were conducted using uniformly distributed sources inside homogeneous forests covering complex terrain to link the spatial patterns of scalar turbulent fluxes to topographic features. Results showed strong modulation of the fluxes by flow features induced by topography, including large area with negative fluxes compensating “chimney” regions with fluxes almost an order of magnitude larger than the landscape flux. Significant spatial heterogeneity persisted up to at least two canopy heights, where most eddy‐covariance measurements are performed above tall forests. A heterogeneity index was introduced to characterize and contrast different scenarios, and a topography categorization was shown to have predictive capabilities in identifying regions of negative and enhanced fluxes.