Interdecadal Variability of East Asian Summer Atmospheric Rivers: Dominant Modes and Their Transition in the Late 1970s

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Abstract Based on seven reanalysis data sets and three atmospheric river (AR) detection algorithms, we investigate the dominant interdecadal modes of East Asian (EA) summer atmospheric rivers (ARs) from 1940 to 2024. The first mode exhibits a monopole pattern characterized by coherent AR enhancement, associated with a low‐level anomalous anticyclone and an intensified western North Pacific subtropical high (WNPSH). The anomalous anticyclone is maintained by the meridional wave train induced from the western tropical Pacific under the anomalous Indo‐West Pacific Walker circulation triggered by the negative sea surface temperature anomalies (SSTAs) over the southern Indian Ocean (IO), which is closely linked to the IO Basin mode. The second mode presents a zonal dipole pattern featured by opposite AR anomalies, corresponding to a pair of low‐level anomalous cyclonic and anticyclonic circulations and the northeastward WNPSH retreat. The dipole circulation is mainly sustained by the meridional wave train excited from the Maritime Continent (MC) when cold tropical eastern Pacific SSTAs and warm MC SSTAs generate an anomalous Pacific Walker circulation, accompanied by the combined effect of a wave train from the mid‐latitudes. The second mode is significantly modulated by the Pacific Decadal Oscillation. Particularly, the dominant EA AR mode varied from the monopole to dipole modes around 1977/1978 due to changes in oceanic forcing from the Indian to the Pacific Ocean, leading to a shift in EA AR frequency from an increasing trend to a relatively stable state.

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