长江流域月降水的时空变化及其与AO/NAO的时滞相关分析

Analysis on spatiotemporal variability of monthly precipitation and its lag correlation with AO and NAO in Yangtze River Basin

运用旋转经验正交函数(REOF)和交叉小波变换方法,分析了长江流域1960—2012年月降水的时空分布特征及其与AO/NAO的时滞相关关系。结果表明:(1)长江流域月降水异常分布的局域特征明显,可划分为4个主要的空间异常型:两湖平原型、东南丘陵型、西南型及北方型;(2) 4个主要的空间异常模态的累计贡献率达45. 8%,其中REOF1(18. 9%)的正异常区位于巫山及两湖平原地区;东南丘陵一带为REOF2(12. 3%)的正值中心,REOF3(8. 9%)突出了云贵高原北部和四川盆地南部的正异常区; REOF4(5. 7%)的负值中心处于四川盆地北部及其以北地区。这4个模态的时间系数(RPCk)的变化幅度较大,且其位相均呈不规则的正负交替,表明各降水异常区具有复杂的时间演变特征;(3) 4个主要异常模态与AO、NAO在特定时间尺度皆存在显著相关的现象,巫山及两湖平原地区、四川盆地北部及其以北地区的月降水均对AO表现出及时响应;东南丘陵一带的月降水对AO、NAO的最佳滞后响应时间都较长。

The spatiotemporal variability of monthly precipitation and its lag correlation with AO and NAO from 1960 to 2012 in Yangtze River Basin are analyzed by applying the rotated empirical orthogonal function(REOF) and cross wavelet transform. The results are as follows:(1) The local characteristics of the anomalous distribution of monthly precipitation in the Yangtze River Basin are obvious. It can be divided into four main spatial anomalies: the plain of Hubei and Hunan type, southeast hill type and southwest type and north type;(2) The cumulative contribution rate of the four major spatial anomalies is 45.8%. REOF 1 (18.9 %) reveals that the positive anomaly area of this mode is located in Wushan and the plain of Hubei and Hunan, the southeast hilly area is the positive value center of the second mode REOF 2 (12.3 %), REOF 3 (8.9 %) highlights the northern Yunnan Guizhou Plateau and the southern Sichuan Basin as the positive anomaly area of this mode, and the negative center of the fourth mode REOF 4 (5.7 %) is located in the northern part of Sichuan Basin and areas to its north. The variation ranges of the four modes’ time coefficients are large, and their phases all show irregular positive-negative alternations, indicating complicated temporal evolution characteristics in different precipitation anomaly zones.(3) Each mode shows significant correlation with both AO and NAO at certain time scales. Monthly precipitation in Wushan, the plain of Hubei and Hunan, the northern part of Sichuan Basin and regions to its north all show timely responses towards AO, while the optimum response time of monthly precipitation in the southeast hilly area towards AO and NAO are both longer.