8.19华北暴雨模拟中微物理方案的对比试验

在中尺度模式多种物理过程中,微物理过程是一个非常关键的环节,其不仅直接影响降水预报,而且也影响模式的动力过程.微物理方案有明确的物理基础,但是在实际暴雨模拟中,究竟采取哪一种方案的结果更理想,需要深入比较,因为不同的微物理方案对降水模拟结果有着很大的差异.本文利用中尺度非静力模式WRF (V3.2.1版本),采用36 km、12 km和4 km的格点分辨率,选用七种微物理方案,对2010年8月18~19 日华北地区的暴雨过程进行了敏感性试验.从降水落区和强度方面对总降水的预报性能进行了对比,模拟结果表明:选用不同的微物理方案,可以不同程度地模拟这场暴雨的范围和强度,且选择合理的微物理方案对细网格（4 km）嵌套的模拟也可以相应的提高,从而提高了暴雨模拟的分辨率,为暴雨中小尺度成因分析提供了参考.其中,水平分辨率为36 km时,Lin方案模拟的雨带范围和降水强度与实况拟合的最好；水平分辨率为12 km时,Thompson方案模拟的强降水位置、强度与实况最为接近；而水平分辨率为4 km时,WSM6方案模拟的强降水位置、强度与实况拟合得较好.再结合垂直速度、涡度、散度和雨水混合比等基本物理量的诊断分析,可以更好地理解各微物理方案对降雨预报的影响,所得的结论对我国华北暴雨强降水预报和中尺度模式微物理过程在业务和研究方面有相当的参考价值.

The Effects of Different Microphysical Schemes in WRF on a Heavy Rainfall in North China during 18-19 August 2010

There are kinds of physical processes in the mesoscale model, in which, the microphysical process is of vital importance. It makes direct effect on the dynamical process of the model and the precipitation forecast as well. Different physical schemes have different physical basis, in the simulation of torrential rain, they will produce distinct results. It needs detailed comparison to justify which scheme has better performance in the heavy rain simulation. A heavy rainfall in North China during 18-19 August 2010 is simulated using the weather research and forecast modeling system (WRFV3.2.1 version). The study is carried out with seven microphysical schemes with the 36-km, 12-km, and 4-km resolutions, respectively. From the rainfall area and intensity of precipitation,forecast performances (model performance) are compared. The simulation results show that different microphysical schemes can result in different degrees of simulation effect including the scope and intensity of the rain. Reasonable selection of microphysical schemes can also improve the fine-mesh (4 km) nested simulation accordingly, thereby improving the resolution of the rainstorm simulation, which provides reference in the analysis of small- and medium-scale rainstorm. The project with the grid size of 36 km indicates that: by comparison, the simulated rainfall location and intensity with the Lin scheme are closer to observed ones. For 12-km resolution, Thompson scheme performs better than other schemes in simulating both the heavy rainfall center and strength. When the grid resolution reduced to 4 km, WSM6 scheme performs best. Combined with the diagnosis of the basic physical quantities, such as vertical speed, vorticity, divergence, and the rain mixing ratio, the role that microphysical schemes play in the rainfall forecast can be better understood. The conclusion is of certain reference value in the rainfall forecast and the mesoscale model microphysical processes in operation and research.