Analysis of flux footprints in fragmented, heterogeneous croplands

IF 1.9 4区地球科学 Q3 METEOROLOGY & ATMOSPHERIC SCIENCES

Meteorology and Atmospheric Physics Pub Date : 2024-02-15 DOI:10.1007/s00703-023-01004-w

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引用次数: 0

Abstract

An accurate quantification of fluxes from heterogeneous sites and further bifurcation into contributing homogeneous fluxes is an active field of research. Among such sites, fragmented croplands with varying surface roughness characteristics pose formidable challenges for footprint analysis. We conducted two flux monitoring experiments in fragmented croplands characterized by two dissimilar surfaces with objectives to: (i) evaluate the performance of two analytical footprint models in heterogeneous canopy considering aggregated roughness parameters and (ii) analyze the contribution of fluxes from individual surfaces under changing wind speed. A set of three eddy covariance (EC) towers (one each capturing the homogenous fluxes from individual surfaces and a third, high tower capturing the heterogeneous mixed fluxes) was used for method validation. High-quality EC fluxes that fulfill stationarity and internal turbulence tests were analyzed considering daytime, unstable conditions. In the first experiment, source area contribution from a surface is gradually reduced by progressive cut, and its effect on high-tower flux measurements is analyzed. Two footprint models (Kormann and Meixner ‘KM’; analytical solution to Lagrangian model ‘FFP’) with modified surface roughness parameters were applied under changing source area contributions. FFP model has consistently over predicted the footprints (RMSE_FFP = 0.31 m⁻¹, PBIAS_FFP = 19.00), whereas KM model prediction was gradually changed from over prediction to under prediction towards higher upwind distances (RMSE_KM = 0.02 m⁻¹, PBIAS_KM = 8.50). Sensitivity analysis revealed that the models are more sensitive to turbulent conditions than surface characteristics. This motivated to conduct the second experiment, where the fractional contribution of individual surfaces (α and β) to the heterogeneous fluxes measured by the high tower (T3) was estimated using the principle of superposition (FT3 = α FT1 + β FT2). Results showed that α and β are dynamic during daylight hours and strongly depend on mean wind speed (U) and friction velocity (u*). The contribution of fluxes from adjoining fields [1 − (α + β)] is significant beyond 80% isopleth. Our findings provide guidelines for future analysis of fluxes in heterogeneous, fragmented croplands.

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分析破碎、异质耕地中的通量足迹

摘要准确量化来自异质场地的通量，并进一步将其分叉为同质通量，是一个活跃的研究领域。在这些地点中，具有不同表面粗糙度特征的破碎耕地给足迹分析带来了巨大挑战。我们在以两种不同表面为特征的破碎耕地中进行了两次通量监测实验，目的是：(i) 评估两种分析足迹模型在异质冠层中的性能，同时考虑到粗糙度参数的聚合；(ii) 分析风速变化时来自单个表面的通量贡献。方法验证使用了一组三个涡度协方差（EC）塔（每个塔捕获来自单个表面的同质通量，第三个高塔捕获异质混合通量）。考虑到白天的不稳定条件，对符合静止性和内部湍流测试的高质量 EC 通量进行了分析。在第一个实验中，通过渐进式切割逐渐减少了表面的源面积贡献，并分析了其对高塔通量测量的影响。在改变源面积贡献的情况下，应用了两个修改了表面粗糙度参数的足迹模型（Kormann 和 Meixner "KM"；拉格朗日模型的解析解 "FFP"）。FFP 模型对足迹的预测一直偏高（RMSEFFP = 0.31 m-1，PBIASFFP = 19.00），而 KM 模型对上风距离的预测从偏高逐渐变为偏低（RMSEKM = 0.02 m-1，PBIASKM = 8.50）。敏感性分析表明，模型对湍流条件比对表面特征更敏感。这促使我们进行了第二次实验，利用叠加原理（FT3 = α FT1 + β FT2）估算了各个表面（α 和 β）对高塔（T3）测量的异质通量的贡献率。结果表明，α 和 β 在白天是动态的，与平均风速 (U) 和摩擦速度 (u*) 密切相关。来自邻近区域的通量[1 - (α + β)]在 80% 等距线以外的区域具有重要作用。我们的研究结果为今后分析异质、破碎耕地的通量提供了指导。

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来源期刊

Meteorology and Atmospheric Physics 地学-气象与大气科学

CiteScore

4.00

自引率

5.00%

发文量

审稿时长

6-12 weeks

期刊介绍： Meteorology and Atmospheric Physics accepts original research papers for publication following the recommendations of a review panel. The emphasis lies with the following topic areas: - atmospheric dynamics and general circulation; - synoptic meteorology; - weather systems in specific regions, such as the tropics, the polar caps, the oceans; - atmospheric energetics; - numerical modeling and forecasting; - physical and chemical processes in the atmosphere, including radiation, optical effects, electricity, and atmospheric turbulence and transport processes; - mathematical and statistical techniques applied to meteorological data sets Meteorology and Atmospheric Physics discusses physical and chemical processes - in both clear and cloudy atmospheres - including radiation, optical and electrical effects, precipitation and cloud microphysics.