近57年江苏省雷暴变化趋势特征分析

VARIATION TRENDS OF THUNDERSTORMS IN JIANGSU FROM 1951 TO 2007

利用江苏省1951—2007年雷暴资料,采用气候倾向率、小波分析和保证率等气候诊断方法,探讨江苏省近57年雷暴的气候变化趋势、周期性特征、时空分布规律和不同保证率下初终期分布。结果表明:江苏省雷暴日数年际变化整体呈减少趋势,主要表现在夏季和秋季雷暴日数的减少。而春季的多年变化不明显。江苏省每10年雷暴日数减少约2天。在年代际变化中,年雷暴日数明显的正距平期主要分布在1960年代初、1960年代末—1970年代初中期,1980年代后期、1990年代后期。负距平期主要出现于1970年代后期—1980年代中期、1990年代中后期和1990年代后期—本世纪初期。不同保证率下雷暴初日、终日存在明显地区差异,50%保证率下雷暴初日(终日)在3月中旬—4月上旬(9月上旬—下旬),80%保证率下雷暴初日(终日)在3月下旬—5月上旬(10月上旬—下旬)。在周期分布上,江苏8～10 a以上的周期都相对比较稳定且具有全域性,而相对较短的周期一般都不具有全域性,从长周期分析江苏地区近几年年雷暴日数各地均处于偏多的周期内。

With the data of thunderstorms in Jiangsu province from 1951 to 2007, the climatological variation trends, periodicity features, temporal-spatial distribution, and initial and ending dates of thunderstorms under different assurance ratios during the recent 57 years, are analyzed by means of climatic trends, wavelets analysis, and assurance ratios. The result shows that the annual number of thunderstorm days has a decreasing trend. Decreasing trends mainly exist in summer and autumn, but they are not significant in spring. On average, there are decreases of about two thunderstorm days per decade. For the interannual change, the periods with large positive departures mainly happen in the early 1960s, from the late-1960s to the early-and middle-1970s, and late-1980s and 1990s. The negative departure periods are from the late-1970s to the mid-1980s, the mid- and late-1990s, and from the late-1990s to the early 2000s. Under different assurance ratios, the initial and ending dates of thunderstorms show large differences from one area to another. For an assurance ratio of 50%, the initial thunderstorm dates occur from the third pentad of March to the first pentad of April while the ending dates from the ftrst pentad to the last pentad of September. At an assurance ratio of 80%, the initial （or ending） dates of thunderstorms occur from the last pentad of March to the first pentad of May （or from the first pentad to the last pentad of October）. The results from the wavelets analysis show that the variation periods are stable and exist across the whole region when they are more than 8-10a, but they have no such features when the periods are shorter. Over the past few years, the number of thunderstorm days all distributes in periods of larger concentration in Jiangsu, according to the analysis of long periods.