The linkage between two ENSO types/modes and the interdecadal changes of ENSO around the year 2000

This study focuses on the interdecadal changes in ENSO properties emerging around the year 2000. Compared to 1980-1999, after 2000, the ENSO amplitude weakened, the occurrence of the central Pacific （CP） Et Nino increased, and the eastern Pacific （EP） El Nino became suppressed. Meanwhile, the dominant period of ENSO shortened from quasi-quadrennial （QQ） to quasi-biennial （QB）. The authors show that these changes in ENSO properties are evidently consistent with the change in the stability of the ENSO mode through connecting the two ENSO types with the two coupled ENSO modes, i.e. the QQ and QB modes. It is suggested that the relative activity or stability of the two ENSO modes changed after the year 2000. The intensity of both the QQ and QB mode weakened. The QQ mode, which is linked to EP ENSO and was significantly strong during 1980-1999, became much weaker after 2000 in terms of the EP type almost disappearing. Compared with the weakness of the QQ mode, the QB mode, as manifested by the CP type, remained active and became dominant in the tropical Pacific after 2000. Analysis shows that the changes in mean states in the tropical Pacific were likely responsible for the interdecadal ENSO changes around the year 2000.

厄尔尼诺和南方涛动(ENSO)在2000年前后发生了明显的年代际变化。与1980-99年相比,2000年以后ENSO的振幅减弱,主周期缩短,中太平洋(CP)型ENSO的发生频率升高,且没有典型的东太平洋(EP)型ENSO出现。本文将两种类型ENSO与两个ENSO模态联系起来,发现ENSO在2000年前后的年代变化实质上是两个ENSO模态的相对活跃性发生了改变:与EP型ENSO相联系的准四年模态在2000年之后活跃性明显降低,与CP型ENSO相联系的准两年模态依然活跃,并成为热带太平洋地区的主模态。分析表明,热带太平洋地区气候平均态的改变可能是这次ENSO年代际变化的主要原因。