本文利用1958～2000年ERA-40再分析每日资料和我国516台站降水资料以及EOF方法, 分析了我国东部季风区夏季降水异常主模态的年代际变化特征及其与东亚上空水汽输送通量时空变化的关系。分析结果表明了我国东部季风区夏季降水的时空变化存在两种主模态: 第1主模态不仅显示出明显的准两年周期振荡的年际变化特征且也有明显的年代际变化, 在空间上具有经向三极子型分布; 第2主模态显示出明显的年代际变化特征, 且在空间上具有经向偶极子型分布。这表明了这两主模态有明显的年代际变化, 在1958～1977年期间我国东部夏季降水异常分布为从南到北 “＋－＋” 经向三极子型分布, 而在1978～1992年期间降水异常出现了与1958～1977年相反的分布, 为从南到北 “－＋－” 经向三极子型分布。然而, 在1993～1998年期间, 由于第2主模态的作用增大, 我国东部夏季降水异常为从南到北经向三极子型与 “＋－” 偶极子型模态的结合, 这使华南夏季降水明显增加。并且, 分析结果还表明: 这两主模态的年代际变化与东亚上空夏季水汽输送通量的时空变化密切相关, 它不仅与东亚和西北太平洋上空似如东亚/太平洋型 (EAP型) 遥相关波列分布的夏季水汽输送通量异常年代际变化有关, 而且与欧亚上空中高纬度西风带似如欧亚型 (EU型) 遥相关波列的夏季水汽输送通量异常年代际变化密切相关。
Interdecadal variation of the leading modes of summertime precipitation anomalies in the monsoon regions of eastern China and its association with the spatio-temporal variations of summertime water vapor transport fluxes over East Asia are analyzed by using the daily data of the ERA-40 reanalysis and precipitation data at 516 observational stations of China for 1958－2000 and the EOF analysis method. The analysis results show that there are two leading modes in the spatio-temporal variations of summertime precipitation anomalies over the monsoon region of eastern China: The first leading mode exhibits not only a characteristic of obvious interannual variation with a quasi-biennial oscillation, but also a feature of interdecadal variability, and its spatial distribution is of a meridional tripole pattern. And the second leading mode exhibits a characteristic of obvious interdecadal variability, and its spatial distribution is of a meridional dipole pattern. This shows that these two leading modes have a significant interdecadal variability. During the period of 1958－1977, the distribution of summertime precipitation anomalies in eastern China exhibited a “＋－＋” meridional tripole pattern from the south to the north, and the distribution of precipitation anomalies for 1978－1992 showed a “－＋－” meridional tripole pattern in the region, which was opposite to that for 1958－1977, but during the period of 1993－1998, since the role of the second leading mode in summertime precipitation anomalies in eastern China was intensified, the distribution of summertime precipitation in this region showed a combination of “＋－＋” meridional tripole pattern and “＋－” meridional pattern, which caused the increase of summertime precipitation in South China. Moreover, the analysis results also show that the interdecadal variation of these two leading modes is closely associated with the spatio-temporal variations of summertime water vapor transport fluxes over East Asia, which is associated not only with the interdecadal variation of the EAP pattern teleconnection-like wave-train distribution of summertime water vapor transport flux anomalies over East Asia and the western North Pacific, but also with the interdecadal variation of the EU pattern teleconnection-like wave-train distribution of summertime waver vapor transport flux anomalies in the westerly zone over middle and high latitudes of Eurasia.