Comparative analysis of damage surveys and observations with two different types of wind disaster

Abstract

Damage survey, conventional observations and Doppler weather radar data are used to analyze the tornado occurred on 8 June 2018 at Nanhai District in Foshan City and microbursts occurred on 18 August 2016 at Leizhou County in Zhangjiang City. Results show that Nanhai tornado intensity is rated F1 and EF1 and the microburst at Leizhou is rated F2 and EF2. The flows caused by microburst have multiscale and small spatio-temporal scale characteristics. Two high wind events both occurred in the environmental conditions including low-level convergence, upper-level divergence and superposition of strong jet at mid and low levels. The tornado occurred in the inner region of typhoon Ewiniar, while the microburst occurred in the peripheral of typhoon Dianmu. Environmental parameters are shown to be relatively weak conditional instability, low convection inhibition and low condensation uplift height. However, the low level(0-1 km) vertical wind shear in the tornado case is much stronger. Two storm cells are both accompanied by mesocyclones. However, the mini supercell forming the tornado has obvious hook echo feature, which is accompanied by medium-intensity mesocyclones, and the scale of mesocyclones is much smaller. The mesocyclone has the smallest scale and the lowest vertical extension height when tornado appears. The microbursts are formed in an elliptical β mesoscale storm which is accompanied by moderate to strong mesocyclone. The mesocyclones have divergent rotating structure with higher base height and larger diameter. Features of mid-level radial velocity convergence and strong reflectivity factor core drop can be detected when the microbursts come.

Keywords

• damage survey
• tornado
• microburst
• environmental conditions
• radar echo feature