Downstream Amplification of Rossby Waves in Summertime Heavy Precipitation Events Over the Korean Peninsula

Abstract We investigate the characteristics of long‐lasting summertime heavy precipitation events (HPEs) over South Korea associated with quasi‐stationary atmospheric rivers (QSARs) based on the 29‐year (1996–2024) daily column water vapor (CWV) from the ERA5 reanalysis data and the Global Precipitation Climatology Project (GPCP) precipitation data. Through a case study and composite analysis, we found that the QSARs in the Pacific region gradually moved westward toward Korea, resulting in the stagnation of large amounts of CWV and precipitation near Korea. The dynamical mechanisms of the HPEs associated with the QSARs are investigated based on the finite‐amplitude local wave activity (LWA) calculated using the ERA5 reanalysis data. Downstream amplification of the LWA, which is associated with the westward movement of the Pacific QSAR, occurred approximately 1 week before HPEs over South Korea. These results suggest that LWA offers the potential to be used in forecasting long‐duration HPEs in South Korea in summer.