Different Influence of Two Intraseasonal Oscillations on the Spring Long-Lived and Medium-Lived Consecutive Cloudy-Rainy Events in the Yangtze-Huaihe River Valley

In this study, the mechanisms for the long-lived and medium-lived regional consecutive cloudy-rainy events (RCCREs) in the Yangtze-Huaihe River valley (YHRV) are investigated by comparing the influences of 10–30-day and 30–90-day intraseasonal oscillations (ISOs). The evolution of medium-lived RCCREs is generally dominated by the 10–30-day ISO, while the 10–30-day and 30–90-day ISOs synergistically contribute to the occurrence of long-lived RCCREs. Further analysis reveals that, when the East Asian westerly jet (EAWJ) shifts northward to the north of YHRV, a RCCRE in the YHRV occurs in 2 days later. In the medium-lived RCCREs, the EAWJ retreats southward rapidly; while in the long-lived RCCREs, the stronger 30–90-day ISO prevents the southward retreat of EAWJ, which favors the persistence of the RCCREs in the YHRV. The northward shifted EAWJ facilitates the RCCREs by modulating the secondary atmospheric circulation, consequently enhancing the moisture convergence and ascending motion anomalies over the YHRV. The RCCREs-related precursor wave train originates from northern Europe with at least a 4-day lead. The wave train propagates southeastward to excite an anomalous high over East Asia, which contributes to the northward shift of EAWJ and subsequently the occurrence of RCCREs. Different from the rapid weakness of the precursor wave train associated with the medium-lived RCCREs, the precursor wave train associated with the long-lived RCCREs can be maintained by the 30–90-day ISO, which consequently leads to a persistence of the northward located EAWJ and long-lived RCCREs in the YHRV.