中文摘要：

新疆北部汛期（7～8月）降水量具有明显的年际和年代际变化．针对年代际、除去年代际后年际和不同年代际背景下年际变化三种时间尺度，利用NECP／NCAR再分析资料，分析相应的大气环流．结果表明，三种时间尺度降水变化的物理机制不同，年代际背景非常重要．新疆北部汛期降水异常时，欧亚中高纬环流系统具有相当正压结构的显著异常．从气候角度和年代际大气环流变化，提出新疆年代际增湿存在索马里越赤道急流到新疆的三段式水汽接力输送方式，索马里急流和热带印度洋是中亚和新疆的重要水汽补充源之一．

英文摘要：

The precipitations in north Xinjiang in rainy seasons （July and August, or JA） show distinct interannual and interdecadal variations. In this study, analyses are performed by using NECP/NCAR reanalysis data on respectively atmospheric circulation anomalies associated with three time scales, which are interdecadal, interannual after remoying interdecadal variation, and interannual variations on different interdecadal backgrounds. The results show that there are different physical mechanisms for three time scales, and interdecadal backgrounds are important. Remarkable equivalent-barotropic structure circulation anomalies over Eurasia mid-high latitude are responsible for rainfall anomalies in Xinjiang. It is pointed out from climate and interdecadal circulation change that there are vapor anomalies associated with 3 - segment relayed transportation from Somali jet stream to Xinjiang. Both Somali jet stream and tropical India Ocean are also the important vapor resources for mid - Asia and Xinjiang.