涡动相关仪和大孔径闪烁仪观测通量的空间代表性

Investigation of Spatial Representativeness for Surface Flux Measurements with Eddy Covariance System and Large Aperture Scintillometer

在对涡动相关仪和大孔径闪烁仪足迹模型进行敏感性分析的基础上,利用北京密云站2006年8月至2007年12月期间的观测资料,应用足迹模型对观测通量的空间代表性做了初步的分析。结果表明:涡动相关仪和大孔径闪烁仪的源区对风向、Monin-Obukhov长度,空气动力学粗糙度和观测高度/有效高度等因子比较敏感。密云站涡动相关仪的源区白天主要分布在仪器的西南与南面,而夜间则在东北与北面。大孔径闪烁仪的源区为西南—东北向分布。涡动相关仪各月源区形状不同,但大致分布在南北长1000 m、东西宽850 m的范围内,而LAS各月源区为西南—东北向分布,长约2060 m,最宽处约为620 m。对涡动相关仪通量有贡献的下垫面主要为园地(67%)和耕地(19%)。其中园地的通量贡献比例在夏、秋季比较大,冬、春季稍小,而耕地则相反。大孔径闪烁仪的主要通量贡献源区为园地、耕地和居民地,通量贡献比例分别为49%,28%和11%。其中园地和耕地通量贡献率的变化趋势与涡动相关仪的观测结果一致,但没有涡动相关仪的变化明显。

Based on the analysis of sensitivity of analytical footprint models of an eddy covariance system （EC） and a Large Aperture Scintillometer （LAS）, as well as the observation of EC and LAS at Miyun flux station of Beijing （from August 2006 to December 2007）, the flux spatial representativeness of EC and LAS were preliminarily analyzed. The results are as follows： （1）The source areas of EC and LAS are sensitive to wind direction, Monin-Obukhov length, aerodynamic roughness length and measurement height. （2）The source areas of the eddy covariance system distribute in the southwest and south area during the daytime, while in the northeast and north area during the nighttime. The source areas of the LAS are in the direction from southeast to northwest. The source areas of the eddy covariance system are dif- ferent in each month, but all locate in an area of 1000m （S--N） by 850 m （W--E） area. The source areas of the LAS are in the direction from southeast to northwest in each month, about 2060 m long and 620 m wide. （3）The main types of land use to determine the measured fluxes of the eddy covariance system are orchard （67%） and farmland （19%）. The flux contribution of orchard is larger in summer and autumn, but smaller in winter and spring. And it is contrary for farmland. The primary land use types of flux contribution for LAS are orchard （49%）, farmland （28%） and residential area （11%）. The seasonal variation of flux contribution of orchard and farmland is the same as the eddy covariance system, but it is not obvious.