ENVIRONMENTAL CONDITIONS AND RADAR MONITORING OF THE TORNADO ON JULY 21,2021 IN QINGYUAN DISTRICT,BAODING CITY

WANG Fuxia; YU Xiaoding; XUE Xuewu; PEI Yujie; YANG Luyuci; WANG Zongmin; GUO Zhiqiang; ZHU Gang; WANG Yuhong

doi:10.16032/j.issn.1004-4965.2023.058

Abstract：The current study presented a detailed analysis of the tornado events on July 21,2021,in Donglü Village,Qingyuan District,Baoding City,Hebei Province,by using data from the SA-band Doppler Weather Radar in Shijiazhuang City and the X-Band Phased Array Doppler Weather Radar in Xiong'an New Area,ERA5 Reanalysis data and conventional observations data.The results were as follows:(1)The tornado began at 15:53 and lasted 22 minutes.According to the extent of damage,the tornado was classified as EF2.The tornado was not caused by a typical weather system;instead,there were shear or wind speed convergence areas below 500hPa.The 700 hPa jet stream brought warm and moist air,enhancing instability and increasing vertical wind shear,which facilitated the development of strong convection.(2)The environmental characteristics of the mini-supercell storm that generated the tornado included a convective available potential energy of 1680.3 J/kg.The vertical wind shear for 0～3 km was 17.1 m/s,indicating a strong shear.The vertical wind shear for 0～1 km was 7.1 m/s,while for 0～6 km,it was 7 m/s,indicating a smaller shear.The wet layer was relatively deep,and the lifting condensation level was observed at 316.1 km.(3)The starting and ending time,intensity,extension height,and evolution trend of the mesocyclone above 1 km observed by the SA-band Doppler Weather Radar and the X-band Phased Array Radar were basically consistent.(4)The X-band Phased Array Radar provided precise observations with its high radial resolution and proximity to the tornado.It continuously monitored a low-level mesocyclone below 1 km from 5 minutes before the tornado formation until its end,indicating the imminent occurrence of the tornado.The X-band Phased Array Radar also clearly observed the convergent flow field near the apex of the hook echo with convergence heights reaching more than 2 km,confirming the presence of a convergent flow field along the tornado's path.(5)The rear-side downdraft of the supercell storm was observed by the X-band Phased Array Radar 14 minutes before tornado formation.The temperature of the rear-side downdraft was lower than the environmental temperature.Strong convergence and upward movement were observed in the middle and lower layers of the area where the tornado formed,consistent with the formation mechanism of mesocyclones in the lower layers proposed by American scholars.(6)After the mesocyclone was formed in the lower layer,the X-band Phased Array Radar observed a rapid strengthening of convergence in the lower layers.The tornado formed when the convergence reached its peak,validating the mechanism proposed by American scholars that strong convergence in the lower layers and upward vertical uplift of the strong updraft in the middle layers are necessary for tornado formation.