绿洲灌溉对垂直湍流热通量影响的大涡模拟研究

为了研究湍涡对中尺度绿洲灌溉的响应，利用WRF模式大涡模拟模块（WRF-LES）在西北半干旱区绿洲区开展灌溉前和灌溉后两个大涡模拟试验（分别简称为BI和AI），其中灌溉可能会改变绿洲非均匀强度。利用面积平均的办法计算湍流热通量并利用小波分析将湍流热通量模态分解到不同的尺度。结果表明灌溉增加了土壤湿度，引起绿洲内部非均匀强度增加，灌溉对垂直热通量以及通量频散都有较大影响。AI中的湍涡为网状，与BI中一致。AI与BI中的感热通量的频散高度都随着感热通量的减小而减小。AI与BI中感热通量小波能量谱尺度一致，但是BI中强度比AI小。潜热通量的频散高度依赖于感热通量，且潜热通量能量谱随高度减小。空间滞后相关系数的结果表明由于灌溉前地表加热较强，感热通量对地表热通量的响应高度在灌溉之前（BI）比灌溉后（AI）更高。灌溉后的通量模态的飘移距离小于灌溉前的。

Impact of Irrigation in the Oasis in Northwestern China on Vertical Turbulent Heat Flux Using Large-Eddy Simulation

This study aims to investigate the response of turbulent eddies to mesoscale, heterogeneous, land use change in the oasis in Northwestern China. For this purpose, two experiments were carried out using the WRF-LES model for the experiments before irrigation (BI) and after irrigation (AI), capturing the change of the heterogeneity strength due to irrigation in the oasis. The area-averaged method was used to calculate the area-averaged flux while the wavelet analysis was used to decompose the pattern of surface turbulent heat fluxes into multiscale patterns.The results show that irrigation has an important impact on vertical heat flux, soil moisture, and soil temperature. Irrigation increases the heterogeneity strength, which greatly impacts the dispersion of flux pattern. The dispersion height of sensible heat flux decreases with the decrease in sensible heat flux AI experiment. The shape of turbulent eddies in the AI experiment is reticular, which is similar to that in the BI case, but energy spectra of the sensible heat flux pattern decrease after irrigation. In addition, the dispersion height of latent heat flux depends on sensible heat flux, and energy spectra of latent heat flux pattern decrease in AI experiment. Regarding the results related to the spatial lag correlation coefficient, the height of the response of the vertical heat flux to the surface flux in BI is higher than the one in AI. The shift distance in AI is shorter than that in BI. Strong surface heating leads to large correlation coefficients and strong entrainment at the top of convective boundary layer.