不同分辨率和微物理方案对飑线阵风锋模拟的影响

为研究不同分辨率和微物理方案对飑线阵风锋模拟的影响,利用WRF中尺度数值预报模式,对2009年6月5日发生在上海的一次飑线过程分别进行了3、1、0.5 km水平分辨率和一、二阶矩微物理方案的理想试验。结果表明,模式水平分辨率和微物理方案对模拟飑线阵风锋有明显的影响。随模式水平分辨率的提高,模式模拟的飑线弓状回波结构更精细。与3 km分辨率相比,1和0.5 km分辨率模式能很好模拟出飑线后部下沉气流和前部上升气流,模拟的冷池前沿最大风速相对更接近实况。二阶矩微物理方案更能模拟出飑线弓状回波前强后弱的结构特征和飑线过境地面降温幅度,模拟的飑线移动速度、冷池面积和强度、冷池前沿最大风速和雨水蒸发率等均小于一阶矩微物理方案的模拟值。采用1和0.5 km模式水平分辨率及二阶矩微物理方案模式模拟的飑线与WSR-88D多普勒天气雷达探测实况更接近。模式分辨率的提高有利于模拟飑线的维持。对业务数值预报模式模拟飑线阵风锋而言,在计算条件允许的情况下,模式水平分辨率达1 km并采用二阶矩微物理方案可能是需要的。结果还表明,冷池前沿最大风速、冷池强度、模式底层降温幅度、飑线移动速度与雨水蒸发率存在对应的变化趋势,飑线移动速度的变化对飑线阵风锋地面大风的预报有指示意义。改善数值模式对飑线阵风锋预报性能除需关注模式水平分辨率和微物理方案外,还需关注数值模式对雨水蒸发率的模拟能力。

Study of the influence of the different horizontal resolutions and microphysical setups on the idealized simulation of a squall line

Using the WRF (Weather Research and Forecasting) model, the idealized simulations of the 5 June 2009 squall line event in the Shanghai area are conducted in this paper for exploring the influences of the different horizontal resolutions and microphysical setups on the idealized simulations. Three different horizontal grid spacing, which are 3, 1 km and 0.5 km, and two different microphysical setups, with single-moment and double-moment microphysics, are used. The results show that the simulations of the gust front of the squall line are sensitive to both horizontal resolution and microphysical setup. The higher-resolution model has higher performance on simulating the fine structure of the bow echo in the squall line. Comparing with 3 km, the simulation with 1 km or 0.5 km horizontal resolutions can produce the front updraft and the rear downdraft of squall line clearly with similar gusts to each other. The double-moment microphysics simulations can produce the more reasonable bow echo structure of squall line and drops in temperature on the surface with slower movement, less cold pool area and intensity, less gust and less rainwater evaporation than the single-moment microphysics. Comparison against the WSR-88D observations shows that 1 km or 0.5 km horizontal resolution with the double-moment microphysics setup produces more realistic simulation than the others. The finer resolution is benefitial to simulating the evolution of squall line. For simulating the gust front of squall line, the operational NWP model maybe requires 1 km horizontal resolution with the double-moment microphysics setup. Furthermore, the evolution of gust, cold pool intensity, rate of cooling in the bottom of model, propagation of squall line and rainwater evaporation show a similar trend of evolution. The propagation speed of squall line is indicative of gust forecast. For improving the NWP performance of gust prediction, not only must horizontal resolution and microphysics setup be paid more attentions to, but also rainwater evaporation simulation must be improved.