关键词: 龙卷, 对流有效位能, 垂直风切变, 气温

Abstract: 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 (E_CAPE) 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 E_CAPE , S₀₆, and their products (ES = E_CAPE×S₀₆) suggested that the centers of ES were more coincided with areas of frequent tornados. The significant decreasing in S06 in Jul.-Aug. of 1980-2009 in North China Plain might be responsible for the reduction of tornados in the plain after the 1980s.

Key words: tornado, convective available potential energy, vertical shear of wind, air temperature