signature=ef3e82acb9c8bcbda0842267436c4261,Observations of the tornado occurred at Foshan on 4 Octob...

Observations of the tornado occurred at Foshan on 4 October 2015

LI Zhaohui;WANG Donghai;MAI Xuehu;WU Kailu;LIU Ying;WANG Hongyan;ZHU Jianjun;YAN Lijun;LI Cailing;CHEN Huixian;LONG Yanyan;Foshan Meteorological Bureau Foshan Tornado Research Center;School of Atmospheric Sciences,Sun Yat-Sen University;State Key Laboratory of Severe Weather,Chinese Academy of Meteorological Sciences;Civil Aviation Flight University of China;

A tornado,rated as a category 3 storm on the enhanced Fujita scale(EF3),occurred at Foshan as part of Typhoon"Mujigae"(2015)between 15:28 BT and16:00BT4 October 2015.This tornado lasted for 32 min and destroyed a large number of factories and houses.The tornado swath was about 31.7 km,and the largest tornado swath diameter reached up to577 m.Photos and tornado videos were collected in the survey of damages caused by the tornado.In addition,the surface automatic weather station data,regular observational data,and Doppler radar data were used in this paper to analyze this tornado process.The tornado life cycle was divided into three stages:The developing stage,the mature stage,and the dissipating stage.The tornado moved faster in the developing and mature stage than in the dissipating stage when it slowed down due to changes in the intensity of the supercell and surface roughness.The large-scale circulation featured by obvious wind shear and high moisture in the lower levels was favorable for the tornado genesis.Cold air extended to the south as the small trough stretched southward in the surface layer,high SWEAT index,high K index and low lifting condensation level(LCL)were found in the unstable layer.These were necessary environmental conditions for tornado genesis.The bell shape terrain of the Pearl River Delta region is also favorable for the development of convergence and local vortex genesis in the surface layer.The variables recorded by the surface automatic weather stations showed strong signals when the tornado passed by.The distribution of 3 s gust and 3 s minimum pressure extended along the northwest—southeast direction,which was consistent with the tornado swath.The pressure and temperature dropped sharply while the wind speed increased dramatically during the tornado development period,and cyclonic convergent winds circled around the tornado.The rainfall started to increase 5 to 10 min before the tornado arrived,and the main rainfall zone was located to the left of the tornado path,indicating that the tornado was situated in the right-rear flank of the supercell.The pressure was higher and temperature was lower after the tornado left than that before the tornado came.The Tornadic Vortex Signature(TVS),the hook echo,and bounded weak echo region were detected when the tornado touched down.The heights of the TVS's top,base and the centroid decreased as the storm strengthened and descended to the lowest level when the tornado touched down on the ground.The wind shear was much higher than that of the detected mesocyclone,which also increased when the tornado touched down.

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