中国东部夏季季节内降水异常及其伴随的热带和中高纬度大气环流演变特征

利用1981—2020年夏季（5—8月）CPC（Climate Prediction Center）逐日降水资料、NCEP/NCAR逐日再分析资料以及NOAA的向外长波辐射资料，通过经验正交函数（EOF）分解、超前滞后合成等方法，分析了中国东部夏季季节内降水异常的主要模态（即南方型和江淮型降水异常）及其伴随的热带和中高纬度大气季节内振荡（ISO）信号演变特征，初步讨论了中国东部夏季季节内降水异常的成因。结果表明:（1）南方型降水异常事件在早、中、晚夏发生次数接近，江淮型降水异常事件主要发生在中夏。（2）早夏南方型降水异常主要表现为长江以南降水异常，中、晚夏长江以北的降水异常也比较明显。（3）南方型降水异常的形成受到热带和中高纬度大气季节内振荡的共同影响，热带大气对流信号传播携带的暖湿气流输送与中高纬度大气罗斯贝波列传播伴随的冷空气活动在南方地区形成水汽辐合，有利于降水异常的发展维持。且热带和中高纬度大气季节内振荡信号受海表温度、副热带高压和西风急流季节内变化的调节。从早夏、中夏到晚夏，热带大气季节内振荡的源地和传播路径均发生变化，中高纬度对流层高层罗斯贝波列的传播路径和强度也有差别。（4）江淮型降水异常主要表现为长江中下游和华南沿海降水异常反相变化，并伴随着西太平洋副热带高压的西伸东退。热带从赤道西太平洋北传和西北传的异常对流信号，以及中高纬度乌拉尔山阻塞高压与鄂霍次克海阻塞高压在季节内尺度上的协同变化，是造成江淮型降水异常的主要原因。 

Intra-seasonal summer precipitation anomaly over eastern China and evolution characteristics of its associated tropical and mid-to-high latitudes atmospheric circulation

Based on CPC(Climate Prediction Center)daily precipitation data,NCEP/NCAR daily reanalysis data and NOAA outgoing longwave radiation data from May to August for the period 1981-2020,the characteristics of main modes of summer intraseasonal precipitation anomalies in eastern China(named Southern type and Jiang-huai type precipitation anomalies)and the evolution features of associated atmospheric intra-seasonal oscillation(ISO)signals in tropical and mid-to-high latitudes are analyzed using EOF decomposition and lead-lag composite analysis.The causes of intra-seasonal precipitation anomalies are preliminarily discussed as well.The results show that:(1)The Southern type precipitation anomaly events are almost evenly distributed in early,middle and late summer,while the Jiang-huai type precipitation anomaly events mainly occur in middle summer.(2)In early summer,the Southern type precipitation anomalies are mainly presented as precipitation anomalies in the south of the Yangtze River,and in middle and late summer,while the precipitation anomalies in the north of the Yangtze River are also significant.(3)The Southern type precipitation anomaly events are affected by atmospheric ISO signals in the tropical and mid-to-high latitudes.The warm and moist air transport carried by the tropical atmospheric convection and the cold air activity accompanied by the propagation of the Rossby wave train in the mid-to-high latitudes generate water vapor convergence in the southern region,which is conducive to the development and maintenance of precipitation anomalies.In addition,atmospheric ISO signals in the tropical and mid-to-high latitudes are modified by intra-seasonal variations of sea surface temperature,subtropical high and jet stream.From early summer,mid-summer to late summer,the ISO source and propagation path of the tropical atmosphere have changed,and the propagation path and intensity of the Rossby wave train in the upper troposphere at mid-to-high latitudes are also different.(4)Reversed change of the middle and lower reaches of the Yangtze River and South China coast appears during Jiang-huai type precipitation anomaly events,accompanied by the east-west movement of the Western Pacific Subtropical High.The convective anomaly propagating northward and northwestward from the equatorial western Pacific Ocean and the intra-seasonal combined variation of the blocking highs over the Ural Mountains and the Sea of Okhotsk at mid-to-high latitudes are the main reasons for the formation of Jiang-huai type precipitation anomalies.