基于近地层垂直速度能谱尺度特征确定复杂下垫面零平面位移

本文利用位于南京市郊区的南京大学仙林校区SORPES观测站多层湍流观测数据分析了湍流谱特征,以白天不稳定条件下垂直速度能谱谱峰对应的长度尺度也就是离地高度为判据,探讨了运用该方法确定复杂下垫面零平面位移的可行性。统计分析表明,该方法确定的长度尺度呈现出较为一致的概率分布形状,概率最大的长度尺度对应于离地高度,在复杂下垫面情况下这个高度就是零平面位移高度到观测高度之间的距离,将观测点的离地高度减去这个距离就能得到零平面位移。本文同时运用不稳定条件下垂直速度方差在近地层中的相似关系来确定零平面位移,并与谱方法得到的结果进行对比。结果表明,谱方法和方差法得到的零平面位移非常接近。

Determining the zero-plane displacement height of complex surface from the length scale of vertical velocity power spectra measured in surface layer

This article analyzes the characteristics of turbulence spectra by using multi-layer turbulence observation data from the SORPES observation station at the Xianlin Campus of Nanjing University,located in the suburbs of Nanjing.Based on the criterion that the length scale corresponding to the vertical velocity power spectra peak under unstable conditions during the day (the ground height),the feasibility of this method used to determine the zero plane displacement of complex underlying surfaces was explored.Statistics show that the shapes of probability distribution of the length scales of the spectral peak at the two heights are similar,and the length scale with the maximum probability can be regarded as the height from the level of zero-plane displacement.The zero-plane displacement heights derived from the measurement data at the two levels are almost the same.Additionally,the zero-plane displacement height is also determined by using the relationship between the vertical velocity variance and stability parameter.Results show that the zero-plane displacement heights derived the two methods are close to each other.