Improving the energy balance closure over a winter wheat field by accounting for minor storage terms
Improving the energy balance closure over a winter wheat field by accounting for minor storage terms
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DOI：
10.1016/j.agrformet.2018.10.012
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发表时间：
2019-01-15
影响因子：
6.2
通讯作者：
Streck, Thilo
中科院分区：
文献类型：
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作者：
Eshonkulov, Ravshan;Poyda, Arne;Streck, Thilo
通过涡流协方差 (EC) 技术测量的地表湍流通量通常远小于净辐射和地面热通量之间的差值。这称为能量平衡闭合（EBC）问题。它对于验证陆地表面模型至关重要，因为它会给能量通量的大小和分配带来很大的不确定性。能量平衡的差距要求在土壤-植物-大气系统中寻找额外的能量项。为了评估这些次要储存条件对测量 EBC 的贡献，我们进行了一项实验研究，以评估这些次要储存条件对德国西南部 Kraichgau 地区连续两个生长季（2015 年和 2016 年）测量 EBC 的贡献。测量和计算的次要存储项包括植物冠层的焓变（S-e）、空气的焓变（S-a）、光合作用和呼吸作用的能量消耗和释放（S-p）以及大气湿度变化（S-q）。此外，还确定了 EC 足迹内不同位置的土壤蓄热量 (S-g)，并与 EC 站的 Sg 单点测量结果进行比较。进行量热和谐波分析来计算地面热通量。由于植物生长的生产阶段二氧化碳净吸收量较高，S-p 在改善 EBC 方面具有最强的效果。 2015年，所有次要存储条件合计EBC平均增长5.0%，5月份最高值达到7.4%，而2016年平均增长6.8%，5月份增长8.4%。基于板块数据的调和分析计算出的地面热通量比量热法将 EBC 缩小了 3%。总之，通过考虑次要存储条件并对地面热通量数据应用谐波分析，可以实现更好的 EBC。关于未来的研究，我们建议重点关注能源术语的全年测量，因为在生长季节储存的能量可能会在一年中的其余时间从系统中损失掉。尽管如此，次要能量项对 EBC 的显着贡献表明，当所有缺失的能量都被假设为湍流时，湍流能量通量很可能被高估，例如通过鲍文比闭合后方法校正通量时的典型方法。
Turbulent fluxes at the land surface measured by the Eddy Covariance (EC) technique are typically considerably less than the difference between net radiation and ground heat flux. This is known as the energy balance closure (EBC) problem. It is crucial for validating land surface models as it provokes substantial uncertainty to the magnitude and partitioning of energy fluxes. The gap in the energy balance calls for searching for additional energy terms in the soil-plant-atmosphere system. To evaluate the contribution of these minor storage terms to the measured EBC, we conducted an experimental study to evaluate the contribution of these minor storage terms to measured EBC in the Kraichgau region in southwest Germany over two consecutive growing seasons (2015 and 2016). The measured and calculated minor storage terms comprised the enthalpy change in the plant canopy (S-e), the air enthalpy change (S-a), the energy consumption and release by photosynthesis and respiration (S-p), and the atmospheric moisture change (S-q). Furthermore, the soil heat storage (S-g) was determined at different locations within the EC footprint and compared to the single point measurements of Sg at the EC station. Calorimetric and harmonic analysis were performed to compute ground heat flux. S-p had the strongest effect in improving EBC due to the high net CO2 uptake during the productive phase of plant growth. In 2015, all minor storage terms together increased EBC by 5.0% on average, with a maximum value of 7.4% in May, while the improvement in 2016 was 6.8% on average and 8.4% in May. Ground heat flux computed with the harmonic analysis based on plate data narrowed the EBC by 3% more than the calorimetric method. In summary, a better EBC can be achieved by considering minor storage terms and applying a harmonic analysis to ground heat flux data. Regarding future research, we recommend to focus on year-round measurements of energy terms because energy stored during the growing season might be lost from the system during the rest of the year. Nonetheless, the significant contribution of minor energy terms to EBC indicates that turbulent energy fluxes are most likely overestimated when all the missing energy is assumed to be turbulent the typical approach when fluxes are corrected by the Bowen ratio post-closure method for instance.