Atmospheric Rivers in East Asia Summer as the Continuum of Extratropical and Monsoonal Moisture Plumes

Abstract East Asian atmospheric rivers (ARs) exhibit the most pronounced activity in summer with significant impacts on monsoon rainfall. However, their occurrence mechanisms are yet to be revealed in detail. In this study, we unravel the inherently complex nature of East Asian summer ARs by applying a multiscale index that quantifies the relative importance of high-frequency (HF) and low-frequency (LF) moisture transports in AR development. It is found that both HF and LF processes contribute to shaping the summertime ARs in East Asia, contrasting to the wintertime ARs dominated by HF processes. Stratification of ARs with the multiscale index reveals that HF-dominant ARs are driven by baroclinically deepening extratropical cyclones, analogous to the widely accepted definition of canonical ARs. In contrast, LF-dominant ARs result from an enhanced monsoon southwesterly between a quasi-sta…