Studies On The Characteristics And Potential Forecasting Of Tornadoes In China

Tornado is a funnel-shaped cloud column with violently rotating destructive winds. Because of the small scale and short life cycle, it is very difficult to detect and even harder to predict the tornado, which will definitely cause huge losses of both life and wealth. China is one of the favorable countries for occurring of tornadoes, especially for eastern China. Currently, the tornadoes over China are under the concern of Chinese scholars. How to make an accurate prediction for tornadoes is not really clear and deserves detailed investigation. In order to forecast the tornadoes and to reduce the influence and loss caused by the tornadoes, an environmental analysis using some of the existed parameters for Chinese tornadoes in nearly ten years were performed. Then further analysis of actual tornadoes’ weather and environmental conditions has been done. Quantitative analyses of the differences between the tornadoes and non-tornadic condition have been done to create a universal tornadic index designed to forecast activity in tornadic environment. We have also discussed the possibly effect of the cloud microphysical mechanism of aerosol on tornado occurrence.We have used reanalysis system from 2002 to 2009 and found that favorite significant tornado environments were concentrated in the eastern of China, most particularly in the southeast the East and the northeast. The potential regions as well as the potential numbers of tornadoes in China had an obvious decreasing trend. Tornadoes occurred as "westerly trough after the warm ridge" in Southern China, and as "subtropical high edge type "in Eastern China. Tornadoes can also happen result from typhoons. The wet-on-dry unstable stratification、high CAPE(>1500J kg-1)、 nearing the lower limit of 0-6km wind shear(3 X 10-3s-1) and exceeding the lower limit of 0-lkm wind shear (5×10-3s-1) in supercell were the common environmental conditions.An index has been formulated according to the analysis of tornadoes and non-tornadic cases. Firstly, meeting the conditions of severe thunderstorm is needed: ①CAPE≥550J kg-1,②1.6371og(S6)+2.3161og(CAPE)≥8.30.Then,we need to distinguish the tornadic and non-tornadic environment:③250S1-mlLCL≥1000,④S1 Ⅵ5m s-1,⑤mLCL≤1000m.CAPE is convective available potential energy, S1 and S6 represent for 0-1 km and 0-6 km vertical wind shear, mlLCL is lifting condensation level. The hit rate was about 23% for the period of 2004-2011 which had increased a dozen percentage compared to the past. The high value forecasting areas and actual high value area were almost the same, except for Guangxi、Zhejiang and other provinces.The concentration of aerosol is characterized by the cloud droplet concentration, and sensitivity experiments with three different cloud droplet concentration (3000cm-3,1000cm-3 and 100cm-3) are conducted to investigate the cloud microphysical impacts of aerosol on the tornadogenesis using the Advanced Regional Prediction System(ARPS) model. We could find the structure of the supercell thunderstorm in all three experiments. However, there are some differences in the structure and evolutions between the three, tornadic vortexes are all formed from the matured to the demise of the thunderstorm. In high concentrations of cloud droplets trial, tornadoes could be stronger and longer-lasting, which indicates effects on tornadoes result from changes in aerosols.The results of this study have created a universal tornadic index designed to forecast activity in tornadic environment. We have also explored the effects of the cloud microphysical processes on the occurrence and development on tornadoes. All the findings provide basis for the forecasting and warning of tornadoes in the future. If we can join the cloud microphysical aspects into the index or using the consultation of satellites and radar data analysis needs an ongoing effort on the research.