利用1981-2019年西北地区4月降水站点资料、美国国家环境预报中心第二套再分析资料（NCEP/DOE Ⅱ）、美国国家海洋和大气管理局（NOAA）海温场资料,研究了西北地区4月降水的异常特征以及对应的同期环流场特征,寻找可能的前兆海温信号并讨论其影响机制。结果表明：（1） 西北地区4月降水以全区一致性分布为主,具有明显的年际与年代际变化。（2） 当东北大西洋至东亚上空存在一个“负、正、负、正”的异常波列分布时,使得巴尔喀什湖低槽偏强,东亚大槽减弱,西北地区盛行显著的偏南气流,上升运动加强,加之来自东部海洋与孟加拉湾充足的水汽输送,在西北区形成强烈的水汽辐合区,有利于该区降水偏多;反之,情况则相反。（3） 前期2月北大西洋三极子指数与西北地区4月降水呈显著的正相关关系,可作为4月降水预测的前兆信号。进一步分析表明,北大西洋海温异常产生的非绝热加热可以激发Rossby波能量的下游频散,致使欧洲西部、乌拉尔山、巴尔喀什湖、东北亚地区呈现“负、正、负、正”的遥相关波列,而这种异常Rossby波能量频散与4月降水异常对应的Rossby波能量频散非常相似,从而影响到西北地区4月降水异常。

Using April precipitation data from stations in northwest China from 1981 to 2019, NCEP/DOE reanalysis data, and NOAA sea temperature field data, the anomalous characteristics of April precipitation in northwest China and the characteristics of the synchronous circulation field are studied to identify possible precursor SST signals and discuss influence mechanisms. The results indicate the following. (1) April precipitation in northwest China is, for the most part, uniformly distributed over the entire region, with obvious interannual and decadal changes. (2) When there exists a “negative, positive, negative, and positive” anomalous wave train distribution from the Northeast Atlantic to East Asia, the low trough over Balkhash Lake is relatively strong, the large trough over East Asia is weak, and a significant southerly airflow prevails in the northwest China with significant upward movement. In addition, sufficient water vapor transport from the eastern ocean of China and the Bay of Bengal form a strong water vapor convergence area in the northwest China, which is favorable to precipitation in northwest China. For the converse distribution, the situation is opposite. (3) In early February, the North Atlantic tripole index shows a significant positive correlation with the April precipitation in the northwest China; this can be used as a precursor to the April precipitation forecast. Further analysis shows that the non-adiabatic heating due to SST anomalies in the North Atlantic can stimulate the downstream dispersion of Rossby wave energy; as a result, Western Europe, the Urals, Balkhash Lake, and Northeast Asia present a “negative, positive, negative, and positive” teleconnection pattern. This type of abnormal Rossby wave energy dispersion is consistent with that of the abnormal precipitation in April, which affects the abnormal April precipitation in the northwest region of China.