Persistent precipitation extremes in the Yangtze River Valley prolonged by opportune configuration among atmospheric teleconnections

This study investigates whether and how three synoptic-scale teleconnections, i.e. East Asia/Pacific teleconnection (EAP), Silk-Road teleconnection (SR) and Eurasia teleconnection (EU), induce persistent precipitation extremes (PPEs) in the Yangtze River Valley. Results show that only the EAP teleconnection has the potential of independently incurring PPEs; while the other two teleconnections' influences on PPEs need to be exerted via their liaison with the EAP pattern. Cases are accordingly grouped into two subsets, i.e. single EAP-PPEs and three teleconnection-PPEs. In both groups, the EAP teleconnection evolves following a similar pathway that poleward energy dispersion dynamically links a westward-extended subtropical high, a deepened midlatitude trough and the Okhotsk blocking. EAP-induced circulation anomalies enhance low-level convergences and upper-level divergences, convey exceptionally abundant moisture, and hence give birth to a quasi-stationary front leading to PPEs in the Yangtze River Valley. Despite similarities, PPEs last noticeably longer in the three-teleconnection context. The EU teleconnection-related downstream energy dispersion at higher latitudes favours both earlier establishment and latter decay of the Okhotsk blocking. Constructed meridional flows at mid-high latitudes continuously steer migratory disturbances southeastward into the EAP trough. The SR plays a bigger role during the latter half of PPE life span (3 days after onset) via stimulating new cyclonic disturbances that largely overlap with the EAP trough spatially. Moreover, EU- and SR-excited disturbances could effectively extract baroclinic and barotropic energy from local mean flows to replenish components of the EAP tripole pattern, which therefore survives longer and prolongs PPEs by several days.