南京雷暴天气异常的环流背景分析

使用南京站地面和高空观测资料及NCEP/NCAR再分析资料,对南京地区2000—2012年的雷暴天气特征进行了分析。南京全年和夏季雷暴日数分别呈现准5年和2～3年周期变化,年平均雷暴日数为30.6 d,其中夏季雷暴日数最多,平均为22.4 d,占全年总雷暴日数的73.1%,春季雷暴次之,平均为5.2 d,秋季和冬季最少,仅为2.2 d和0.8 d;南京雷暴天气的周期变化与环流异常密切相关,500 hPa高度上,北方低槽加深,夏季副热带高压系统西伸北抬,700 hPa和850 hPa环流调整导致中低层湿度增加;天气尺度垂直上升运动的强度是造成雷暴强度偏强、短时强降水和瞬时大风等灾害天气更加剧烈的重要原因。

Analysis of Circulation Background of Thunderstorms Anomalies in Nanjing

By using surface and upper air data from Nanjing observation station and NCAR/NCEP reanalysis data, characteristics of thunderstorms in Nanjing during 2000~2012 were analyzed, and following conclusions are drawn. Firstly, the annual and summer thunderstorm days in Nanjing show quasi-5 years and quasi-2~3 years cycle variations, respectively. Average number of annual thunderstorm days is 30.6 days, and about 73.1% of thunderstorm occurs in summer and the average number of thunderstorm days is 22.6 days. The average numbers in spring, autumn and winter when thunderstorm occurs less are 5.2 days, 2.2 days and 0.8 days, respectively. Secondly, cycle variations of Nanjing thunderstorm are closely related to circulation anomalies e.g. north trough deepening and subtropical high developing during summer in 500hPa and humidity increasing in lower 700hPa and 850hPa levels. Finally, intensity of vertical upward motion of synoptic-scale may cause thunderstorms with larger daily precipitation and extreme strong wind.