Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany
Evaluating multi-year, multi-site data on the energy balance closure of eddy-covariance flux measurements at cropland sites in southwestern Germany
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DOI：
10.5194/bg-16-521-2019
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发表时间：
2019-01
期刊：
影响因子：
4.9
通讯作者：
Ravshan Eshonkulov;Arne Poyda;J. Ingwersen;H. Wizemann;Tobias K. D. Weber;Pascal Kremer;P. Högy;Alim Pulatov;T. Streck
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作者：
Ravshan Eshonkulov;Arne Poyda;J. Ingwersen;H. Wizemann;Tobias K. D. Weber;Pascal Kremer;P. Högy;Alim Pulatov;T. Streck
抽象的。涡旋协方差(EC)测量的能量平衡通常不是封闭的，这导致了评估和解释EC通量数据的主要挑战之一。能量平衡关闭(EBC)是验证和改进区域和全球气候模型的关键。为了研究农业生态系统EBC缺口的性质，我们分析了德国西南部两个气候反差地区(Kraichgau-KR-和Swabian Jura-SJ)的EC测量结果。数据是从2010年到2017年在六个设备齐全的EC站点获得的。能量平衡比(EBR)是由湍流通量和有效能量的商计算出来的，它与剩余能项之间的关系通过普通线性回归来量化。为了检查EBC差异的潜在原因，我们比较了不同环境条件下的EBC，并调查了各种可能的控制措施。总体而言，EBC的变化在冬季比夏季更大。此外，我们确定，地点对EBC有统计上显著的影响，但对作物和地区都没有显著影响(KR和SJ)。所有欧共体站点的时变足迹是根据2015年测量的数据估计的，并辅之以沿盛行风向的微地形分析。年平均能量平衡差值最小，KR为17%，SJ为13%。最高的EBR主要是来自盛行风向的风。在不稳定的大气条件、强浮力和高摩擦速度下，EBRS的扩散明显缩小。由于增加了同质性，较小的占地面积导致了更好的EBC。在相应的风力条件下，风速计后盖造成的流动扭曲对EBC产生了负面影响。
Abstract. The energy balance of eddy-covariance (EC) measurements is typically not closed, resulting in one of the main challenges in evaluating and interpreting EC flux data. Energy balance closure (EBC) is crucial for validating and improving regional and global climate models. To investigate the nature of the gap in EBC for agroecosystems, we analyzed EC measurements from two climatically contrasting regions (Kraichgau – KR – and Swabian Jura – SJ) in southwestern Germany. Data were taken at six fully equipped EC sites from 2010 to 2017. The gap in EBC was quantified by ordinary linear regression, relating the energy balance ratio (EBR), calculated as the quotient of turbulent fluxes and available energy, to the residual energy term. In order to examine potential reasons for differences in EBC, we compared the EBC under varying environmental conditions and investigated a wide range of possible controls. Overall, the variation in EBC was found to be higher during winter than summer. Moreover, we determined that the site had a statistically significant effect on EBC but no significant effect on either crop or region (KR vs SJ). The time-variable footprints of all EC stations were estimated based on data measured in 2015, complimented by micro-topographic analyses along the prevailing wind direction. The smallest mean annual energy balance gap was 17 % in KR and 13 % in SJ. Highest EBRs were mostly found for winds from the prevailing wind direction. The spread of EBRs distinctly narrowed under unstable atmospheric conditions, strong buoyancy, and high friction velocities. Smaller footprint areas led to better EBC due to increasing homogeneity. Flow distortions caused by the back head of the anemometer negatively affected EBC during corresponding wind conditions.