利用1966—2011年西藏自治区那曲地区所辖7个气象站的雷暴天气历史观测资料，综合运用天气学及线性统计方法、小波分析方法，分析那曲地区雷暴日数的时间和空间分布规律及影响因素。结果表明：那曲地区的雷暴日数存在显著减少趋势，减少趋势达到0．01的显著性水平，变化倾向率为每10年减少5 d；那曲地区雷暴日数空间分布特征为北部多南部少，东部高山峡谷多于西部湖盆；雷暴日数高值出现在东北部，低值出现在东南部。季节分布为夏季最多，春、秋季相对较少，冬季很少出现雷暴；雷暴初日推迟，而雷暴终日提前，雷暴期有缩短趋势。多雷期、少雷期的差异主要表现在西太平洋副热带高压脊线西伸脊点的经度位置、巴尔克什湖东部至青藏高原处高压脊和高原短波槽的位置和强弱上。那曲地区5—9月雷暴日数存在5～10年、20年两种尺度的周期变化规律，从不同时间尺度周期的变化趋势可以看出那曲地区将逐渐进入多雷期。%Using synoptic meteorology,linear statistical methods and wavelet analysis,thunderstorm data from seven meteorological observatories in Nagqu Prefecture from 1966 to 2011 are analyzed to find the trend and space distribution of the number of thunderstorm days and influencing factors.A significant decreasing trend is found in the number of annual thunderstorm days,and the decreasing rate is around five days per decade.The cause for this trend might be that stronger latitudinal atmospheric circulation and weaker lon-gitudinal circulation in the context of global warming reduces the intensity and frequency of cold air,and the mechanical lifting of moist air,which is not conductive to the formation of thunder clouds.Spatially, there is a deceasing number of thunderstorm days from the north to the south,from high mountainous val-leys in the east to plains in the west with the highest number of thunderstorm days in the northeast and the lowest in the southeast.This feature is closely associated with differences in topography,thermal condi-tions,moisture conditions and climate across the prefecture.Due to high temperatures and strong convec-tive activities in summer,there are significantly more thunderstorm days in spring and fall,and there are less thunderstorm days in winter with cold drying weather and relatively stable atmospheric stratification. As the weather becomes drier in winter,thunderstorms start later and end earlier with a decreasing trend in the period of thunderstorm activity within a year.The inter-annual difference in the number of thunder-storm days mainly depends on the westward move of the subtropical high over the West Pacific Ocean,the position and strength of the ridge line between the east Lake Balkhash high and the Tibetan Plateau high, and the shortwave trough off the Tibetan Plateau.When the west Pacific subtropical high weakens or moves eastward,and the warm moist airflow is prevalent in Nagqu,the number of thunderstorm days is higher.When the west Pacific subtropical high strengthens or moves westward,and the northwest airflow is prevalent in Nagqu,the number of thunderstorm days is lower.Two variation periods of 5-10 years and 20 years are found in the number of mean annual thunderstorm days between May and September. These variations indicate that Nagqu Prefecture will experience a period of a higher number of thunder-storm days .
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