Intraseasonal Variations in Spring East Asian Subtropical Jet: Role of Mid–High Latitude Wave Trains and Influence on Rainfall Anomalies in China

Abstract The spring East Asian subtropical westerly jet (EAWJ) is one of the most crucial atmospheric circulation systems, significantly influencing spring precipitation in China. In this study, by applying the empirical orthogonal function (EOF) analysis to the 200-hPa zonal wind anomalies, the first two dominant modes of the spring EAWJ are extracted. The principal components (PCs) of the two EOF modes (PC1 and PC2) exhibit a dominant periodicity of 10–30 days according to the power spectrum analysis results and show significant lead–lag correlations. Therefore, eight phases of the spring EAWJ intraseasonal variations are identified based on the PC1 and PC2, representing the spring EAWJ intraseasonal variability (EAWJ_ISV). Phases 1–4 of EAWJ_ISV exhibit northward EAWJ shifts with positive zonal wind anomalies over Mongolia–Northeast China. The northward-shifted EAWJ can enhance the moisture convergence and ascending motion over the Yangtze–Huai River valley (YHRV) by modulating secondary atmospheric circulation, consequently facilitating more precipitation over the region, and thus increase the probability of extreme precipitation events and regional consecutive cloudy-rainy events (RCCREs). Conversely, phases 5–8 are unfavorable for regional water vapor transport and upward motion, therefore, the spring precipitation intensity over the YHRV is relatively weak, and the probability of extreme precipitation events and RCCREs is also weak. Most rainy days (71.2%) occur in phases 1–4, while dry days (71.3%) occur in phases 5–8. Further analysis indicates that the EAWJ_ISV is influenced by an intraseasonal wave train over mid–high latitude Eurasia from the Ural Mountains to East Asia. Significance Statement The spring East Asian subtropical westerly jet (EAWJ) significantly influences spring precipitation in China. Using the empirical orthogonal function (EOF) analysis on 200-hPa zonal wind anomalies, the first two dominant modes of the spring EAWJ are extracted. Their principal components (PC1 and PC2) exhibit a 10–30-day periodicity and significant lead–lag correlations, forming the eight phases of EAWJ intraseasonal variability (EAWJ_ISV). Phases 1–4 feature positive zonal wind anomalies over Mongolia–Northeast China, reflecting a northward EAWJ shift. By modulating secondary atmospheric circulation, this enhances moisture convergence and ascending motion over the Yangtze–Huai River valley (YHRV), increasing precipitation and extreme precipitation events and regional consecutive cloudy-rainy events (RCCREs) over the region. Conversely, phases 5–8 weaken water vapor transport and upward motion, reducing YHRV precipitation intensity and extreme events. For each phase of the EAWJ_ISV, there is a well-organized wave train that propagates southeastward from the Ural Mountains to East Asia. Such a result indicates that the EAWJ_ISV is influenced by the intraseasonal wave train over mid–high latitude Eurasia.