基于大涡模拟对两类典型边界层参数化方案的评估分析

Evaluation of Two Typical PBL Parameterization Schemes Based on Large-Eddy Simulation Result

在WRF模式的三维动力框架和同一种外强迫下,基于大涡模拟结果对Yonsei University(YSU)和Mellor-Yamada-Janiic(MYJ)边界层参数化方案进行了评估。模式初始场由一个探空观测给定,模式的外强迫为观测得到随时间变化的地面感热、潜热通量及辐射传输模式得到的辐射冷却率。通过显式解析边界层的大涡模拟试验和采用边界层参数化方案的模拟试验结果表明,与大涡模拟结果相比,YSU方案模拟的混合偏强,MYJ方案偏弱;YSU方案模拟的边界层高度偏高,边界层内偏暖、偏干;MYJ方案模拟的边界层高度偏低,边界层内偏冷、偏湿。

The performance of two PBL schemes（YSU and MYJ） is evaluated by the large-eddy simulation（LES） within the same three-dimensional ARW dynamic framework.The model is initialized with a horizontally homogeneous sounding data set upon which a specified diurnal heat flux forcing and radiative cooling rate are imposed.The unique aspects in the approach are the employment of large- eddy simulations as a benchmark and highly idealized experimental design.Our approach is much easier to isolate the errors associated with a particular physical parameterization tested than that by using real-data simulation.Two group simulation test carried on,a group using explicit resolved boundary layer scheme（LES） with 50 meters horizontal resolution,a group using boundary layer parameterization scheme with 1000 meters horizontal resolution.Analysis of potential temperature and water vapor mixing ratio suggests that YSU over-predicts the mixing showing a higher PBL top with warmer,drier PBL structure than those from the LES,and MYJ under-predicts the mixing having a lower PBL top with colder,moister PBL structure.