1980—2009年我国龙卷事件变化

根据1980—2009年我国龙卷事件的变化特征,初步探讨了20世纪90年代以后龙卷事件显著减少的特征及原因。结果表明,1980—2009年龙卷事件呈现明显减少的趋势,20世纪80年代最多,90年代以后明显减少,尤其是夏季(7—8月),在我国东部地区减少最明显。对龙卷高发时段7—8月06时(UTC)对流有效位能(ECAPE)与深层垂直风切变(S06)以及二者乘积变量(ES)的分析表明:ECAPE和S06是影响龙卷的两个重要因子,ES的高值中心更好地对应于龙卷事件发生的集中区。地面气温的变化会影响ECAPE的变化。1980—2009年,我国华北平原地区7—8月S06明显下降是20世纪80年代以后我国华北地区龙卷事件减少的主要原因。

Change Characters of Tornados in China in 1980-2009

Using the 115 tornado events records from 725 stations over China during 1980-2009,geographic and temporal distributive characters of tornado events and reasons for tornado reduction since the 1990s were studied.The results show that tornados frequently occurred in eastern China,and the frequency of tornado events showed a significant decreasing trend in yearly number in 1980-2009,with the highest frequency in the Jul.-Aug.of the 1980s,followed by a distinctly decreasing period,especially in eastern areas.Two important convective parameters,i.e.,convective available potential energy(ECAPE) and vertical shear of 0-6 km wind(S06),in Jul.-Aug.in the period of 1980-2009 were examined to find out reasons for the tornado reduction.The analyses of the centers of ECAPE,S06,and their products(ES = ECAPE× S06) suggested that the centers of ES were more coincided with areas of frequent tornados.The significant decreasing in S06in Jul.-Aug.of 1980-2009 in North China Plain might be responsible for the reduction of tornados in the plain after the 1980s.