利用大涡模式模拟黄土高原地区对流边界层特征

Simulate of Convective Boundary Layer Characteristics in the Loess Plateau by WRF Large-Eddy

边界层湍流所引起各物理量的垂直输送在大气过程中起着重要作用。研究对流边界层特征对分析污染物扩散条件,认识陆气间物质、能量的输送交换机制和提高数值模式模拟能力具有重要意义。受限于目前许多地区通量观测站较少、资料时空分辨率较低,为了研究黄土高原地区大气边界层结构及其特征,将中尺度气象模式WRF(The Weather Research and Forecasting Model)与大涡模式WRF Large-Ed‐dy Simulation(WRF-LES)嵌套使用,分析了黄土高原夏季温湿廓线情形下,由热力驱动的边界层结构特征。结果表明:(1)WRF-LES模拟的地面风温场能较好地显示边界层典型湍流结构,其他气象要素的模拟结果也比较符合边界层实际。(2)混合层顶所在的1000 m高度处垂直湍流强度最大,强夹卷作用导致湍涡尺度减小且涡旋数量增多。(3)在模拟区选定的参数化方案下,采用夏季实际粗糙度0.062 m替换模式默认值0.1 m,发现使用实际粗糙度的模拟温度较之前低0.4 K,与模拟区中心处的观测数据更接近,说明采用合理的粗糙度对提高WRF-LES模拟效果有重要作用。

The vertical transport of physical quantities caused by atmospheric turbulence plays an important role in the atmospheric process.Studying the characteristics of the convective boundary layer is of great significance for analyzing the diffusion conditions of pollutants,understanding the exchange mechanism of materials and en‐ergy between land and air,and improving the ability of numerical model simulation.Due to the limited number of flux observation stations and low spatial-temporal resolution in many regions,in order to study the structure and characteristics of the atmospheric boundary layer in the Loess Plateau,the Weather Research and Forecasting Model(WRF)and the WRF Large-Eddy Simulation(WRF-LES)are nested.The characteristics of the boundary layer structure driven by heat under the condition of summer temperature and humidity on the Loess Plateau were analyzed.The results show that:(1)The surface wind field and temperature field simulated by WRF-LES can display the typical turbulent structure of the boundary layer well,and the simulation results of other meteorologi‐cal elements also conform to the boundary layer law.(2)The vertical turbulence intensity is the highest at the height of 1000 m where the top of the mixed layer is located.The strong entrainment results in a reduction in the scale of the turbulence and an increase in the number of vortices.(3)Under the parameterization scheme selected in the simulation area,the default value of 0.1 m is replaced by the actual roughness in summer of 0.062 m.It is found that the simulated temperature using the actual roughness is 0.4 K lower than before,which is closer to the observed data in the center of the simulated area,indicating that the reasonable roughness is important to im‐prove the simulation of WRF-LES.