Abstract: Based on daily precipitation data at 45 meteorological stations of northern Xinjiang and NCEP/NCAR reanalysis data from June to August during 1961-2017, the threshold of summer extreme precipitation events was determined by using percentile method in northern Xinjiang. The temporal variation characteristics of summer extreme precipitation with different grades and their relationship with maximum daily precipitation in summer and corresponding monthly precipitation were analyzed in northern Xinjiang. The precipitation distribution of twelve cases for wide-range summer extreme precipitation with five-level was clustered by using Euclidean distance method, and on this basis their circulation characteristics were discussed emphatically. The results show that the frequency of summer extreme precipitation with different grades (except for four-level) presented significant rising trend in northern Xinjiang during 1961-2017. The daily precipitation at most stations during the wide-range extreme precipitation process was the maximum daily precipitation in summer of the same year, and the averagely accounted for 28.6% of corresponding monthly precipitation in northern Xinjiang. There were three patterns for the distribution of wide-range summer extreme precipitation in northern Xinjiang. The axis of 200 hPa westerly jet in western Asia subtropical zone was southward, and the westerly winds enhanced in the south of 40°N. The cold air moved southward under the guidance of Ural high pressure ridge, the low value system was active in West Siberia or Central Asia, and the high pressure system was strong in downstream Baikal region on 500 hPa, but the location, range and intensity of these systems were different, which led to different falling areas of wide-range extreme precipitation. Meanwhile, there were anomalous cyclonic and anti-cyclonic water vapor flux anomalies in Central Asia and the lower reaches of eastern Xinjiang, respectively, and the anomalous southward or eastward water vapor transport in northern Xinjiang provided favorable conditions for wide-range extreme precipitation.

Key words: northern Xinjiang, distribution patterns of wide-range extreme precipitation, circulation characteristics, cluster analysis

摘要： 基于1961—2017年夏季新疆北部45个气象站逐日降水资料和NCEP/NCAR再分析资料，采用百分位法确定夏季极端降水事件阈值，分析新疆北部夏季不同等级极端降水频数的时间变化特征及雨量与夏季最大日降水量、同月降水量的关系，并通过欧式距离法对12个5级大范围极端降水个例进行聚类分析，重点探讨大范围极端降水分布的环流特征。结果表明：近57 a新疆北部夏季不同等级（4级除外）极端降水频数均呈显著上升趋势，多数站点5级大范围极端降水量为当年夏季最大日降水量，平均占研究区同月降水量的28.6%。夏季大范围极端降水空间分布表现为3种类型，对应200 hPa西亚副热带西风急流轴偏南，40°N以南地区西风加强，500 hPa乌拉尔山高压脊引导冷空气南下，西西伯利亚或中亚地区低值系统活跃，下游贝加尔湖地区高压系统强盛，但系统位置、范围和强度不同，导致大范围极端降水落区不同。同时，中亚地区和新疆东部下游地区分别存在异常的气旋式和反气旋式水汽通量距平，新疆北部异常偏南或偏东的水汽输送为大范围极端降水的发生提供了有利条件。

关键词: 新疆北部, 大范围极端降水空间分型, 环流特征, 聚类分析