大气湍流是大气的一种重要运动形式，其对大气中的动量、热量、水分和 CO2等交换和输送十分重要，而大尺度涡旋则是其中重要一环。众多的观测数据表明，大尺度涡旋的出现会导致涡动相关仪观测的湍流通量被低估，进而造成能量平衡不闭合问题的出现，也会造成闪烁仪与涡动相关仪的观测差异。对复杂下垫面出现的大尺度涡旋进行研究，有利于进一步阐述地表能量平衡不闭合问题的成因及解释不同观测尺度仪器间的观测差异，为地表水-热-碳过程的精细刻画提供支持。本文基于2012年5-9月在黑河流域中游开展的“非均匀下垫面地表蒸散发的多尺度观测实验:通量观测矩阵”、2020-2021年黑河流域中游大满超级站的涡动相关仪和闪烁仪的观测数据，首先构建基于小波变换和经验模态分解方法的大、小尺度涡旋分离算法，然后在平流日与非平流日进行大、小尺度涡旋的分离工作， 并对比和分析分离结果;最后基于上述方法进行应用，探究大尺度涡旋对地表能量平衡闭合问题的影响，本研究的主要结论如下:
(1)本文改进了两种大尺度涡旋分离方法，主要包括:从高频数据变换尺度提升和小波方差极大值确定指标这两个角度改进小波分析方法，并结合复小波变换完善基于小波变换的大尺度涡旋的分离方法;从引入频谱和进行希尔伯特变换这两个方面改进经验模态分解方法，并定量化表征大尺度涡旋的能量贡献。
(2)基于2012年通量观测矩阵的7月14日与7月31日(平流日与非平流日)数据，小波变换和经验模态分解方法均分离出大尺度涡旋并展现大尺度涡旋随时间的变化规律，二者的分离结果彼此吻合互为补充，但二者的侧重略有不同，小波变换方法对下垫面的异质性较为敏感，经验模态分解方法的适用性更广。
(3)平流的到来会提高能量闭合率，由于观测原理的差异，双波段闪烁仪对大尺度涡旋的捕捉能力优于涡动相关仪，相比涡动相关仪，双波段闪烁仪的能量闭合率提高更大。其中，针对通量观测矩阵:基于复小波变换的涡旋周期结果在绿洲和荒漠下垫面具有明显差异，但在绿洲间的站点差异不明显。大尺度涡旋的能量比例的变化幅度在绿洲下垫面明显大于荒漠下垫面;大尺度涡旋的能量比例的变化与能量闭合率的变化在绿洲下垫面有明显的正相关性。针对双波段闪烁仪的观测数据结论如下:对于涡动相关仪来说，平流时刻相比于非平流时刻能量平衡闭合率平均提高了25.1%;对于双波段闪烁仪来说，平流时刻相比于非平流时刻能量平衡闭合率平均提高了40.1%。由于观测原理的差异，双波段闪烁仪对大尺度涡旋的捕捉能力优于涡动相关仪。

Atmospheric turbulence is an important form of atmospheric motion, which is very important for the exchange and transport of momentum, heat, water and matter in the atmosphere, and large- scale eddies are an important part of it. Numerous observational data show that the occurrence of large-scale vortices will lead to the underestimation of the turbulent flux observed by the eddy covariance (EC) system, and then cause the energy balance unclosed problem. Further, the large scale eddies can also cause the observation difference between the scintillometer and eddy covariance.
Therefore, the study of large-scale eddies on the complex underlying surface is helpful to further explain the causes of the energy balance unclosed problem and explain the observation differences among the observing instruments, and provide support for the fine characterization of land surface processes. Based on the special experiment of " HiWATER-MUSOEXE " conducted in the middle reaches of Heihe River Basin from May to September 2012, and the observation data of eddy covariance and scintillometer (LAS and OMS) at Daman Superstation in the middle reaches of Heihe River Basin from 2020 to 2021, Firstly, a large-scale eddy separation algorithm based on wavelet transform and empirical mode decomposition method is constructed. Then, large-scale eddies are separated on advection days and non-advection days, and the separation results are described, compared and analyzed. Finally, based on the above methods, a case study was carried out to explore the influence of large-scale eddies on the closure of surface energy balance. The main conclusions of this study are as follows:
(1) In this paper, two large-scale eddy separation methods are improved, mainly including: Improving the wavelet analysis method from the two perspectives of scaling up the high-frequency data transform and determining the index by the maximum value of wavelet square difference, and combining the complex wavelet transform to improve the separation method of large-scale eddies based on wavelet transform; The empirical mode decomposition method is improved by introducing spectrum and Hilbert transformation, and the energy contribution of large-scale eddies is quantified.
 (2) Based on the data of July 14 and July 31 (advection day and non-advection day) of the flux observation matrix in 2012, both wavelet transform and empirical mode decomposition method separate large-scale eddies and show the variation rule of large-scale eddies with time. The separation results of the two are consistent with each other and complement each other, but their emphasis is slightly different. The wavelet transform method is more sensitive to the heterogeneity of underlying surface and the empirical mode decomposition method is more applicable.
(3) Advection will improve the energy closure rate. Due to differences in observation principles, the dual-band scintillator has a better capturing ability for large-scale eddies than the eddy covariance instrument. Compared with the eddy covariance instrument, the dual-band scintillator has a greater improvement in the energy closure rate.In terms of flux observation matrix, the vortex period results based on complex wavelet transform have significant differences in oasis and desert underlying surface, but not significant differences between oasis sites. The variation amplitude of the energy ratio of large-scale eddies under oasis is obviously greater than that under desert. There is a positive correlation between the energy proportion of large-scale eddies and the energy closure rate.The observation data of the dual-band scintillator are as follows: for the eddy correlation instrument, the energy balance closure rate at advection time is increased by 25.1% on average compared with that at non-advection time. For dual-band scintillator, the energy balance closure rate at advection time is increased by 40.1% on average compared with non-advection time. Due to the difference of observation principle, the dual band scintillation instrument has better ability to capture large-scale eddies than eddy correlator.