Features Of Tornado In Guangdong Province And The Preliminary Study Of Tornado Early-warning Methods

Tornado is the most violent atmospheric convective weather, which can cause great casualties and property losses incurred. Guangdong, a prosperous economy, large population and is located in the southern region of China, it is a strong convective weather-prone areas, is also one of the major tornadoes occurred, therefore tornado research of Guangdong province has important scientific and practical significance.In this paper, the temporal and spatial distribution and the environmental characteristics of 62 times tornadoes of Guangdong recorded by "Yearbook of China Meteorological Disasters"(2004-2012) were analyzed by sounding data, weather charts and so on, concluded as follow:(1) Tornadoes of Guangdong occurred mainly in April-July, has a good relationship with the South China during the First Rainy Season. High incidence area are Zhanjiang, Foshan and Guangzhou.(2) Tornadoes of Guangdong occurred under ambient atmospheric conditions with a certain degree of instability, manifested as small Showalter index, K index, CAPE and vertical wind shear are great. Compared with other convective weather, tornadoes of Guangdong have lower Lifting Condensation Level and larger low-level vertical wind shear, with mean values were 944hPa and 11.1×10-3s-1.(3) Tornadoes of Guangdong were likely occur in the First Rainy Season and typhoon periphery. Southwest jet is the main reason of the tornadoes of Guangdong in the First Rainy Season, the moist southwest jet play an important role of power and heat, which allows a large low-level vertical wind shear and low lifting condensation level likely to be met; The great low-level vertical wind shear is the main reason for the tornadoes which generated in typhoon.(4) Four types of weather situation can be divided which caused tornadoes of Guangdong:type of typhoon, type of cold fronts, type of warm front pocket area and type of ground convergence line.Doppler weather radar with high spatial and temporal resolution is a powerful tool for identifying and tornado warning. In this paper, tornadoes of Guangdong were anylyzed by Guangzhou Doppler Weather Radar, concluded as follow:(1) The average of speed difference, speed difference of low-level and maximum of speed difference have little difference, the main difference is reflectivity:false alarms of tornadoes are larger than right alarms of tornadoes. Adjustment of the reflectivity threshold of tornado detection algorithms can reduce the possibility of false alarms. This paper shows that when the reflectivity threshold was taken as 20, alarms of tornadoes of Guangdong can achieve the best results.(2) Tornadoes usaually produce in the spiral rain bands of typhoone, bow echo and hook echo of radar images. The enhancement and increase of cyclone can increase the possibility of tornadoes, when TVS appears in the low-level of radar images, indicating tornado has been close to the ground, should be timely warning.