大涡模式水平分辨率对边界层夹卷过程及示踪物垂直传输的影响

Effect of Large Eddy Horizontal Resolution on Simulation of Entrainment and Tracer Vertical Transport

利用敦煌干旱区野外加密观测资料,结合大涡模式模拟研究模式水平分辨率对边界层对流、夹卷过程及示踪物垂直传输的影响。结果表明:模式水平分辨率越高,模拟的边界层对流泡个数越多,尺度越小,且对流强度越强;提高模式水平分辨率,夹卷层位温方差增大,水平速度方差减小,垂直速度方差增大,且上升冷气流对夹卷层热通量的贡献最大。模式水平分辨率越高,垂直速度、位温及示踪物绝对质量浓度概率密度函数分布变化范围相对越广,且模拟的细微变化特征越清晰。另外,提高模式水平分辨率,模拟的示踪物空间分布特征更加细致,示踪物传输高度也较高。综合考虑到分辨率越高在模拟过程中产生的噪音越大且计算时间越久等问题,认为采用200 m水平分辨率时,模式既能较好地模拟出边界层对流的平均结构,又能模拟出边界层湍流的较细微分布特征,是较为理想的选择。

The effects of horizontal resolution of the model on convection,entrainment process and vertical transmission of tracers in boundary layer were studied by using the field intensive observation data in Dunhuang arid area and large eddy model(LEM).The results show when the horizontal resolution of the model was improved,the more the number of convection bubbles,the smaller the scale and the stronger the convection intensity in the boundary layer were simulated.And the potential temperature variance increased,the horizontal velocity variance decreased,the vertical velocity variance increased,and the upward cold flow contributed the most to the heat flux in the entrainment layer.The higher the model horizontal resolution was,the wider the distribution range of probability density functions(PDF)of vertical velocity,potential temperature and tracer concentration were,and the more distinct the subtle variation characteristics were.In addition,the spatial distribution of tracer was simulated to be more detailed and the tracer transport was also higher with increasing the horizontal resolution of the model.Considering the greater noise generated in the simulation process and the longer computing time in the high resolution simulations,the use of 200 m grid spacing as LEM horizontal resolution in simulating was an ideal choice,which could not only simulate the average structure of the boundary layer convection,but also the smaller distribution of the boundary layer turbulence could be simulated.