黑河绿洲区不均匀下垫面大气边界层结构的大涡模拟研究

Large-Eddy Simulation of Atmosphere Boundary Layer over Heterogeneous Land Surface in Oasis Area of Heihe River Basin

采用RAMS模式中大涡模拟的方法,加入高分辨率的植被和土壤资料,模拟了黑河绿洲区(张掖地区)不均匀下垫面条件下大气边界层演变过程。分析了模拟的地表通量、边界层的平均结构和湍流二阶量,并用黑河试验的观测资料检验了模式的模拟性能。结果表明,模拟的平均结构较好地展现了不均匀下垫面条件下边界层内从稳定层结到混合层发展,夹卷层形成,底层逆温层出现,混合层过渡到残留层等的演变过程,呈现出了从初始的稳定边界层发展到对流边界层,最后又形成夜间稳定边界层的日变化规律。湍流二阶量的分析显示,在非均匀下垫面条件下边界层内湍流二阶量的垂直分布与边界层的发展相对应,白天湍流二阶量出现两个峰值,分别位于近地层和混合层顶。与观测资料和现有研究的对比表明,RAMS中陆面模块(LEAF)地表参数不能较好地反映黑河地区的植被特征,模拟的白天地表感热和潜热通量偏小,气温白天偏低、夜间偏高,相对湿度也有偏差。

The atmosphere boundary layer over heterogeneous land surface in oasis area （Zhangye） of Heihe river basin is studied with the large-eddy simulation option of Regional Atmospheric Modeling System （RAMS） by adding highly-resolved land use type and soil texture. The simulated mean structure and second-order moments of ABL are analyzed, and the resulting temperature and relative humidity are compared with the observed data during HEIFE. The results indicate that simulated mean structure correctly exhibit the ABL diurnal variation from primary stable stratification to mixing layer developing and entrainment forming, then inversion appearing and mixing layer evolving to residual layer. The second-order moments show two peaks at surface layer and top of mixing layer respectively. However, because of the difference between the vegetation parameters in land surface model （LEAF） and ones used by simulation of Yan Yuping in Heihe river basin, the simulated surface sensible and latent heat flux are lower than observed in daytime, and so temperature is lower in daytime and higher at nighttime, while deviation of relative humidity is slightly large.