[目的]研究陕北黄土高原夏季降水异常的变化特征及成因.[方法]利用1961 ～ 2008年陕北黄土高原15个测站的夏季降水资料及NCEP/NCAR资料,采用线性趋势估计及合成方法,分析了陕北黄土高原夏季降水的变化特征.[结果]陕北大部分地区夏季降水为减少的趋势,但陕北的西部和南部为增加的趋势.陕北夏季降水有明显的年际及年代际变化特征,20世纪70年代中期至90年代中期为降水相对偏多期,90年代中期以后进入降水偏少期,近年来又有增加的趋势.多雨年在中高纬度地区乌拉尔山西部到贝加尔湖以北为大片的正异常区,表明乌拉尔山有阻塞高压存在；鄂霍次克海以北到贝加尔湖为负异常区.西北太平洋到我国渤海湾以及华北地区为大范围显著正异常区,有利于西太平洋副热带高压的北抬西伸.少雨年的环流配置与此相反,中高纬度为“-、+、-”的波列分布,鄂霍次克海一带为正异常区,西太平洋副高也偏南、偏东.在多雨年,主要的水汽输送来自于东南方向,充沛的水汽造成了陕北夏季降水偏多.少雨年为偏西风转向偏南气流带来的水汽输送,水汽输送明显偏弱且偏东.[结论]该研究为陕北黄土高原夏季降水资源的合理利用提供了参考.%[ Objective] The research aimed to study change characteristics and formation cause of the summer precipitation abnormality in Lo-ess Plateau of northern Shaanxi Province. [ Method ] Based on summer precipitation data of 15 observation stations in Loess Plateau of northern Shaanxi Province and NCEP/NCAR dataset from 1961 to 2008, change characteristics of the summer precipitation in the region were investigated by using linear trend estimation and composite analysis. [ Result] Summer rainfall in most parts of northern Shaanxi Province had decrease trend, but it had increase trend in western and southern regions. The interannual and interdecadal variations were obvious. It had a large a-mount of precipitation from the mid-1970s to the mid-1990s, while summer rainfall had decrease trend after the mid-1990s and increase trend in recent years. In wet years, it was a large positive anomaly zone from western Ural Mountains to northern Lake Baikal at middle and high latitudes , indicating that there was a blocking high over the Ural Mountains, while it was negative anomaly zone from northern Sea of Okhotsk to Lake Baikal. From Northwest Pacific Ocean to Bohai Bay and North China, it was a wide range of significant positive anomaly zone, which was favorable for Western Pacific subtropical high extending westward and northward. The analysis in dry years showed opposite circulation configuration. It was " - , + , - " wave train distribution in middle and high latitudes and positive anomaly zone along the Sea of Okhotsk. Western Pacific subtropical high was also by south and east. Major water vapor was from southeast direction in wet years, and abundant water vapor caused more summer rainfall in northern Shaanxi. In dry years, water vapor was from westerly turning southerly flow. It was weaker and by east. [ Conclusion] The research provided reference for reasonable utilization of the summer precipitation in the zone.
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