Wohlfahrt Georg, Hammerle Albin, Niedrist Georg, Scholz Katharina, Tomelleri Enrico, Zhao Peng
Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA; Institute for Alpine Environment, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY; Institute for Applied Remote Sensing, European Academy of Bolzano, Drususalle 1, 39100 Bolzano, ITALY.
Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, AUSTRIA.
Agric For Meteorol. 2016 Oct 15;226-227:37-49. doi: 10.1016/j.agrformet.2016.05.012.
In complex, sloping terrain, horizontal measurements of net radiation are not reflective of the radiative energy available for the conductive and convective heat exchange of the underlying surface. Using data from a grassland site on a mountain slope characterised by spatial heterogeneity in inclination and aspect, we tested the hypothesis that a correction of the horizontal net radiation measurements which accounts for the individual footprint contributions of the various surfaces to the measured sensible and latent heat eddy covariance fluxes will yield more realistic slope-parallel net radiation estimates compared to a correction based on the average inclination and aspect of the footprint. Our main result is that both approaches led to clear, but very similar improvements in the phase between available energy and the sum of the latent and sensible heat fluxes. As a consequence the variance in the sum of latent and sensible heat flux explained by available radiation improved by >10 %, while energy balance closure improved only slightly. This is shown to be mainly due to the average inclination and aspect corresponding largely with the inclination and aspect of the main flux source area in combination with a limited sensitivity of the slope correction to small angular differences in, particularly, inclination and aspect. We conclude with a discussion of limitations of the present approach and future research directions.
在复杂的斜坡地形中，净辐射的水平测量结果并不能反映下垫面用于传导和对流热交换的辐射能量。利用来自山坡上一个草地站点的数据，该站点在坡度和坡向方面具有空间异质性，我们检验了这样一个假设：与基于足迹平均坡度和坡向的校正相比，对水平净辐射测量值进行校正，考虑各种表面对测量的感热和潜热涡动协方差通量的个体足迹贡献，将产生更符合实际的平行于坡面的净辐射估计值。我们的主要结果是，两种方法都使可用能量与潜热和感热通量之和之间的相位有明显但非常相似的改善。因此，可用辐射解释的潜热和感热通量之和的方差提高了>10%，而能量平衡闭合仅略有改善。这主要是由于平均坡度和坡向在很大程度上与主要通量源区的坡度和坡向相对应，同时坡面校正对特别是坡度和坡向的小角度差异的敏感性有限。我们最后讨论了本方法的局限性和未来的研究方向。
