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Analysis of the energy balance closure over a FLUXNET boreal forest in Finland

机译：芬兰FLUXNET北方森林能量平衡的封闭性分析

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The imbalance in the surface energy budget, when using eddy-covariancetechniques to measure turbulent fluxes, is still an unresolved problem.Important progresses have been reported in recent years identifyingpotential reasons for this lack of energy balance closure. In this paper wefocus on the data collected in a FLUXNET boreal forest site inSodankyl?, Finland. Using one month half-hourly data, an average EnergyBalance Ratio (EBR) of 0.72 is obtained. The inclusion of the heat storageterms in the energy budget yields an improvement of about 6% in the totalclosure. The sensitivity of the energy balance closure to the turbulenceintensity is analysed in terms of the friction velocity, and atmosphericstability/instability conditions. Significant better closure is obtained forhigh values of the friction velocity and unstable conditions. The mismatchin variable footprints for different fluxes is checked by analysing thedependence of the closure on wind direction. The inhomogeneities of theemplacement surrounding the flux tower induce a critical decrease in the EBRof up to 30% for specific wind directions. After filtering allunfavourable conditions, EBR=0.94. This is a reasonable good result for theenergy balance closure. However there is still a 6% of the availableenergy unaccounted. Part of this remaining imbalance could be justified asthe impossibility of the 30 min averaging time to capture the low frequencyflux contributions, since the closure is improved by a 5% when theaveraging time is expanded to 2 h.
机译：当使用涡度协方差技术测量湍流时，表面能收支的不平衡仍然是一个尚未解决的问题。近年来，人们报告了重要的进展，查明了缺乏这种能量平衡封闭的潜在原因。在本文中，我们重点研究在芬兰Sodankyl？的FLUXNET北方森林站点收集的数据。使用一个月的半小时数据，平均能量平衡比（EBR）为0.72。将储热条件包括在能源预算中可以使总封闭面积提高约6％。根据摩擦速度和大气稳定性/不稳定性条件，分析了能量平衡闭合对湍流强度的敏感性。对于高摩擦速度值和不稳定条件，可获得明显更好的闭合效果。通过分析封闭件对风向的依赖性，检查了不同通量的不匹配足迹。对于特定的风向，通量塔周围位置的不均匀性导致EBR的严重降低，最高可降低30％。过滤所有不利条件后，EBR = 0.94。这对于关闭能量平衡是一个合理的好结果。但是，仍然有6％的可用能源尚未解决。这种剩余的不平衡的部分原因可以证明是30分钟的平均时间无法捕获低频通量贡献，因为当平均时间扩展到2 h时，封闭效果提高了5％。

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