Characteristic of Climatologically Statistics about Thunderstorm and the Relationship with Instability Energy in Changsha District in Recent 40 Years

By using the observation data of four meteorological stations' records of thunderstorms over Changsha from 1971 to 2010,studied climatic characteristics of thunderstorms in Changsha. Research results showed that: the space distribution features of thunderstorms day number occurred more in east and west mountain than central plains in Changsha. Liuyang and Ningxiang which in Changsha's east and west,were the highest and second high in number of annual mean thunderstorm days,they were 62 days and 53 days,Mapoling which in the central area annual mean thunderstorm days only 39 days; in the monthly variation,Changsha's thunderstorms mainly occur in February to September,which shows typical of double-peak structure. Thunderstorms happened most frequently in April and August,and in June to September,thunderstorms day number in Liuyang was much higher than Ningxiang,Wangcheng and Mapoling,in the rest month,number of thunderstorm days of four stations had little difference. In daily variation,thunderstorms main appeared in the period of afternoon to evening of four stations in Changsha,of which 15 to 17 most,in 13 to 18,thunderstorms times in Liuyang was obviously more than other three stations. The annual number of thunderstorm days showed a decreasing trend in Changsha during 1971 to 2010,which in Liuyang reduction trend was most obvious. Since 2000,the initial thunderstorm date of Changsha's four stations was slightly delayed and final thunderstorm date significantly advanced; when thunderstorm occurred,Ningxiang on K index and SI index which represented the unstable energy was slightly higher than other three stations.