| Tornado is a most violent and severest convection weather which can accumulate huge unstable energy in a small funnel-form vortex tube and release the energy constantly. Tornado is so devastating that it often pulls up trees, overturneds vehicles and destroies buildings, so it can cause casualties and property damage. Tornado may occur where there are thunderstorms in the world. Tornado is most violent and crinose in the Midwest Plain of USA where we often call it Tornado Alley.In Tornado Alley, there are about100000thunderstorms include10000strong thunderstorm in which there are about1000tornadoes, and in which there will be1000～2000funnels. The peak time of Tornado in USA is from April to August, especially in May. Most of tornadoes in USA are super cell-thunderstorm-tornadoes which are so violent that they can destroy reinforced concrete buildings, so study and forecast of tornado is highly valued by the U.S. government and the public.Tornado can also occur occasionally in China, which is more feeble and rare compared with tornadoes in USA. Hence, it hasnot been paid enough attention to. However, tornado can cause casualties and property damage once it occurs because of high-population-density in the eastern coastal region of China. Therefore, it is scientific and practical to research tornadoes in China.Based on statistical method, synoptics method, physical diagnosis and radar echo analyze and so on and by using Meteorological disasters yearbook from2004to2011, NCEP/NCAR, MICAPS and radar echo data, we analyzed the spacial-temporal characteristic and tTypical case of tornado in Mainland China. The conclusions are as follows,(1) Tornadoes in China are more in plain than in mountainous area, more in coastland than in inland, they concentrate on the following3areas:①Jiangsu, Anhui and Hubei etc., which are part of Yangtze Plain;②Guangdong southern coastal and Hainan;③Part of the Northeast China Plain and the North China Plain. Tornado in china mostly occurs in summer half year. The peak time is from June to August, especially in July.(2) Strength grade of tornado in China mostly is Fl, seldom is F0or F2and no tornadoes above F2.so tornado in china is more feeble.(3) It is hotter and more damp in the area of high-prevalence area of tornado in china, bigger lapse rate of temperature and humidity, assuming the unstable characteristic which is dry-cold in high-level and damp-hot in low-level.when tornado occurs, SI is very low,The whole layer of air column of precipitation is big, Vertical Wind Shear is big and the level of big Vertical Wind Shear is lower than ordinary thunderstorms.(4) Because of Gradually accelerating process of urbanization in china in recent years, more and more high-rise buildings lead to more significant Underlying surface roughness, and mixing layer is becoming higher, which may possibly play a part of the trend that tornado in China is weakening and reducing.(5) Typical Cases of Tornado indicates that when tornado occurs in Yangzhou, whichwas just at the left of upper-level jet stream exit at100～200hPa, and there were infrabar-groove and shear line at500hPa,warm type shear at850hPa, drastic vertical wind shear at1000hPa and depression of the dew point was low.We will lucubrate tornado’s mechanism, the key point for forecasting and relevant safeguard procedures in China. |
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