Estimating the energy balance over forests including advection and horizontal flux divergence

测量地表通量的一个未解决的问题是可用能量（净辐射和由于储存变化引起的热通量之和）与在现场独立测量时的潜热和感热的湍流通量之间的差异。这就导致了所谓的能量平衡不足或闭合问题。关于感热和潜热的估计，有人怀疑被忽视的平流过程是造成这种缺乏的主要原因。此外，有证据表明，能源收支不平衡与其他标量通量（如CO2通量）之间可能存在联系。这对于通常根据涡动协方差测量来估计森林和生物圈的正确CO2吸收汇至关重要。在这个项目的框架内，平流对能量平衡闭合的影响将被检查。两个独特的长期数据集的密集测量活动在不同的森林网站（Tharandt，德国; Renon，意大利）将被用来评估更好地了解平流的作用，能量平衡。将研究垂直和水平平流以及水平通量发散。将讨论储存、异质性和地形对平流通量的影响，以确定在两个地点和其他地方观察到的不平衡的可能原因。

One of the unsolved problems of measuring surface fluxes is the difference between available energy (sum of net radiation and heat flux due to storage changes) and the turbulent fluxes of latent heat and sensible heat when measured independently in the field. This results in the so-called lack of energy balance closure or closure problem. Concerning the estimation of sensible heat and latent heat it is suspected that neglected advection processes are a main contributor to this lack. Also, there is evidence that there may be a link between the energy budget imbalance and other scalar fluxes like CO2 fluxes. This will be crucial for the estimation of correct CO2 sinks of forests and of the biosphere in general typically based on eddy covariance measurements. In the frame of this project the influence of advection on energy balance closure will be examined. Two unique long-term datasets of intensive measurement campaigns at different forest sites (Tharandt, Germany; Renon, Italy) will be used to assess better understanding of the role of advection on the energy balance. Vertical and horizontal advection as well as horizontal flux divergence will be investigated. The influence of storage, of heterogeneity and of topography on advective fluxes will be addressed to identify possible reasons for imbalances observed at the two sites and elsewhere.