Intraseasonal variations in spring East Asian subtropical jet: Role of mid-to-high latitude wave trains and influence on rainfall anomalies in China

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 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 intraseasonal variability of spring EAWJ (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 increased 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%) in phases 5–8. Further analysis indicates that the EAWJ_ISV is influenced by an intraseasonal wave train over mid-to-high latitude Eurasia from the Ural Mountains to East Asia.