采用不同背景场的龙卷模拟结果对比分析

采用常规气象观测资料，对2014年5月21日17:40广州市黄埔区九龙镇一次西风带龙卷的环流背景场进行分析，并利用FNL和ERA5再分析资料作为背景场模拟该龙卷过程，研究了不同再分析场对模拟效果的影响，结果表明:对于雷达回波、垂直速度、水平风场及水成物，FNL资料作为初始场对西风带龙卷的模拟优于ERA5资料。FNL再分析资料作为初始场、边界场能有效地模拟出西风带龙卷的超级单体结构。5月21日17:45对流风暴与经典超级单体结构相似，出现了钩状回波特征与入流缺口，其垂直结构上强回波向东倾斜，形成穹窿结构。17:50超级单体钩状回波处有明显的强上升气流与后侧下沉气流，具备生成龙卷的必要条件；从垂直涡度的低层平面发现涡旋特征十分明显，其高度从250m伸展至2km，龙卷有可能发生在从地面一直延伸至2km向西北倾斜的小尺度气旋内。 

Comparative Analysis of Tornado Simulation Results with Different Background Fields

Using conventional meteorological observations data, the circulation background field of the westerly tornado in Jiulong Town, Huangpu District, Guangzhou City at 17:40, May 21, 2014 is analyzed. FNL and ERA5 reanalysis data are used as the background field to simulate the tornado process, and the influence of different reanalysis fields on the simulation results are studied.The results show that from the analysis of radar echoes, vertical velocity, horizontal wind field and hydromorphic material, the simulation of the westerly tornado with FNL data as the initial field is better than that with ERA5 data as the initial field. The FNL reanalysis data as the initial field and boundary field can effectively simulate the super monolithic structure of the westerly tornado. At 17: 45 on May 21, 2014, the convective storm was similar to the classical super monolithic structure, with hook-like echo features and inlet gaps, and its vertical structure showed that the strong echo tilted to the east to form a dome structure. At 17: 50, there was a strong updraft and a back-side downdraft at the hook echo of the super monomer, which had the necessary conditions to generate a tornado; the vortex features were obvious from the low-level plane of vertical vorticity, which extended from 250m to 2 km in height. Tornadoes may occur in small-scale cyclones ,which is streching northwestward from the ground to 2 km.