上海地区雷暴天气的气候变化及可能影响因素

Climatic Changes Related to Thunderstorm Days And Probable Impact Factors in Shanghai

分析了上海地区雷暴的气候变化及可能影响因素。经验正交函数分析结果表明：上海地区雷暴的年际变化呈较明显的下降趋势；其空间分布主要呈现市区少、郊区多的特点。上海地区的“城市热岛”效应可能会增加城区和城乡交界地区雷暴的发生频数。通过小波分析得到上海地区雷暴日年变化的主周期约为6年。上海地区雷暴异常年6～8月平均大气环流与同期500hPa大气环流特征的关系为多雷暴年整个东亚的位势高度距平场出现大范围的负距平，当年夏季西太平洋副热带高压较弱，位置偏东；少雷暴年则相反。持续型（秋季型）的El Nino事件可能会引起上海地区年雷暴日数异常偏多，而少雷暴年则多为ENSO（El Nino／Southern Oscillation）冷暖事件的更替年。

In this paper, the climate characteristics of thunderstorms in the Shanghai area are analyzed using EOF （Empirical Orthogonal Function） and wavelet analysis methods. The analysis shows a decreasing tendency in the thunderstorm frequency in Shanghai from 1960 to 2004. The thunderstorms are distributed less in the urban areas but more in the suburbs. The influence of the ＂urban heat island＂ may increase the thunderstorm occurrence in the vicinity of the urban areas. It is also shown that the dominant period of the annual thunderstorm variations is about 6 years in Shanghai. In thunderstorm anomalous years, the relationship between the average atmospheric circulation and the geopotential height at 500 hPa from June to August suggests that an obvious negative anomaly exists in eastern Asia. The subtropical high is relatively weak and to the east in active thunderstorm years, and vice verse in less active thunderstorm years. Durative El Nino events are likely to induce the abnormal increment of the thunderstorm frequency while fewer thunderstorms occur in the period of ENSO （El Nino/Southern Oscillation） transformation years.