Analysis of a tornado process over Shantou on 16 June 2011

Using conventional data,radar data,surface intensive automatic weather station observations and NCEP 6-hourly reanalysis data with resolution 1°×1°,a tornado process over Shantou on 16 June 2011 was studied including environment field characteristics and the relationship between tornado and meso-and micro-scale systems on the ground,as well as the dynamic cause etc.The results indicate that the characters of circumstances in favor of tornado occurring in the lower and middle troposphere were: high energy center,strong vertical wind shear,strong wind in the middle troposphere,as well as strong positive horizontal helicity,thick positive vorticity zone and strong convergence in the low level coordinating with strong divergence in the high level.The interaction among synoptic scale,meso-scale and convective storm scale systems resulted in the occurrence of tornado.In the rich vorticity environment,strong echo intensity gradient in thunderstorm cell indicated strong vertical motion gradient in thunderstorm cloud clusters,while the strong vertical motion gradient was the main reason which led to the fast strengthening of the cyclonic rotation of surface wind to generate the tornado.