Eurasian wave-train dynamics modulating July rainfall extremes along the East Asian quasi-stationary rainy front

During the early summer monsoon in East Asia, quasi-stationary frontal precipitation in July accounts for approximately 41% of Korea’s total summer rainfall. Despite including the global warming hiatus period, interannual trends in frontal rain from 1991 to 2024 were not statistically significant across Korea and most of East Asia. Interannual analysis reveals that July precipitation wet years in Korea (JPW-K) are associated with more heavy-rainfall days (> 27.9 mm day⁻ 1 , 90th percentile). In contrast, July precipitation dry years in Korea (JPD-K) exhibit a higher proportion of moderate-rainfall days (< 2.7 mm day⁻ 1 , 50th percentile). This study focuses on 12 representative years—seven JPW-K and five JPD-K years—to examine how Eurasian wave-train dynamics modulate the extreme variability of East Asian frontal rainfall. Upper-tropospheric Eurasian wave-train activity regulates rainfall extremes, with near-surface temperature anomalies emerging as a thermodynamic response to wave-induced changes in circulation. During JPW-K, a wavenumber-3 Eurasian wave train propagated eastward across the continent, inducing blocking highs over eastern Siberia. The primary mechanism driving enhanced July precipitation over Korea during JPW-K is the dynamical circulation anomaly: an intensified subtropical high to the south of ~ 30°N, combined with an anomalous trough and cyclonic circulation over East Asia, strengthened southwesterly moisture transport and convergence toward the Yellow Sea–Korea (YK) region, leading to heavy rainfall. Near-surface temperature anomalies and the associated meridional temperature gradient are interpreted as diagnostic indicators of frontal intensity and as a thermodynamic response to the wave-train-induced circulation, rather than as the primary driver of precipitation anomalies. In contrast, during JPD-K, a wavenumber-5 Eurasian wave train collocated with the subtropical jet at ~ 40°N established a zonally elongated mid-latitude anticyclonic belt that directly suppressed July precipitation over Korea through large-scale subsidence, adiabatic warming, and weakened southwesterly moisture transport.