2014年6月3日佛山龙卷风过程分析

Analysis of the Process of a Tornado June 3,2014 in Foshan

利用广州多普勒天气雷达、常规气象观测和NCEP再分析等资料，分别从环流背景、物理量特征、中尺度特征等方面，对2014年6月3日广东佛山的龙卷风天气过程进行了分析。结果表明：中低层的辐合切变及高层的辐散“抽吸”作用为该次强对流风暴的发生发展提供了有利的大尺度环流背景条件；上干下湿的位势不稳定层结，低层高湿、增温为强对流天气提供了有利的环境条件；冷空气南压和地面中小尺度辐合系统提供了触发机制；K、SI、SWEAT、TT等物理量指数清晰地反映出大气的极端不稳定，中等以上强度的对流有效位能（CAPE）、较低的抬升凝结高度以及较强的0—1km低层垂直风切变为龙卷产生提供了可能性；龙卷等强对流风暴的发展加强与地面中小尺度辐合系统加强有密切关系，珠江三角洲的喇叭口地形以及佛山东南低西北高的独特地理地形条件有利于地面中小尺度辐合系统的形成和加强。多普勒雷达径向速度捕捉到该次龙卷过程的中气旋特征，涡旋持续了6个体扫，垂直伸展局限于3km的低层大气，强度达到了中等到强中等气旋，反射率因子图上最强回波达到60dBz。

With the data of Doppler weather radars in Guangzhou, conventional meteorological observations and NCEP reanalysis, we studied the process of a tornado weather that happened in Foshan, Guangdong on June 3, 2014 by the associated circulation background and the characteristics of physical quantities and mesoscale features. The result is as follows. A converging shear at the middle and low levels and sucking effect at the upper level provided favorable large -scale environmental conditions for the generation and development of this severe convective storm. Favorable environmental conditions also included a geopotentially unstable stratification （ of being drier in the upper level than in the low level） and high humidity and warming in the low level. Southward - progressing cold air and surface meso - and fine - scale converging systems triggered the severe weather. Indexes of physical quantities, such as K, SI, SWEAT and TF, all clearly indicated the extreme instability of the atmosphere ; CAPE was more than moderate, and the height of lifting and condensation was low and the vertical wind shear was strong in the 0 - to 1 - km layer, making it possible for the tornado to take place. The development and enhancement of tornadoes and other severe convective storms are closely related to surface meso - and fine - scale converging systems and the terrain of a bell -mouth shaped estuary of the Pearl River Delta, in association with the unique geographical and topographical conditions of Foshan where it is lower in the southeast than in the northwest, help the systems form and strengthen. During the event, the Doppler radars captured a meso - cyclone with the radial velocity. The vortex lasted for six volume scans with its vertical extension limited to low - level atmosphere below 3 kin. Its intensity was moderate to severe with the strongest echo of reflectivity being 60 dBz on the scan map.