The climatology of atmospheric rivers (ARs) and their roles on precipitation extremes have been extensively researched over western North America and Europe, yet ARs in Asia, especially for those affecting the densely populated countries including Bangladesh, China, India, Thailand and Vietnam are not adequately understood. Here, the climatological characteristics of landfalling ARs, including their frequency and intensity, in the Asian monsoon region for the period 1979-2017 are investigated using the ECMWF ERA-Interim reanalysis dataset. The inter-annual variability of landfalling ARs associated with the combination of the El Niño-Southern Oscillation (ENSO) and the Quasi-Biennial Oscillation (QBO) is presented. The results suggest frequent AR activities over southern India, Indochina Peninsula, southern China, Korea and Japan from May to September. ARs are found to contribute up to 44% of the total summer precipitation over the coastal regions of East Asia and up to 36% in South Asia. Also, ARs are associated with up to 68% of the summer extreme precipitation amount in East Asia and 52-56% in South Asia. The connection between ARs and extreme precipitation is partly explained by the increased precipitation efficiency when ARs occur, indicating a stronger ability of the atmospheric dynamical factors to deplete moisture and generate strong precipitation. The analyses of the combined ENSO-QBO effects on ARs show that ARs in the subtropics tend to become less frequent in the years preceded by an El Niño event due to the weakening of the low-level monsoonal flows associated with the weakened land-sea thermal contrast and upper-level tropical easterly jet, and such modulations tend to become more significant under the easterly phase of QBO.

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forcing strong descending motion and forming an anomalous anticyclone north of the equator. Meanwhile, the positive SST anomalies in the southeastern portion act as a heat source that forces anomalous divergent westerlies and northwesterlies toward the warmer SST area. Thus, anomalous descending motion is induced around the equator.