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

Abstract

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. K E Y W O R D S monsoonal stationary front, persistent precipitation extremes, Rossby wave energy dispersion and conversion, synoptic-scale atmospheric teleconnections, thermodynamic-dynamic mechanisms Q J R Meteorol Soc. 2019;145:2603-2626. wileyonlinelibrary.com/journal/qj © 2019 Royal Meteorological Society 2603 2604 CHEN ET AL.

Synoptic‐Scale Circulation Precursors of Extreme Precipitation Events Over Southwest China During the Rainy Season

“…Previous studies have noted that the eastward‐shifted and enhanced SAH favors summer precipitation over SWC on an interannual time scale (D. Chen et al., 2016) and over the Sichuan Basin on a subseasonal time scale (Ge & Ren, 2019). Previous research reported that more extreme precipitation occurs over the Yangtze River Valley with eastward‐extended intensified SAH (Y. Chen & Zhai, 2015, 2016; Y. Chen, Zhai, et al., 2019; Ning et al., 2017). Our study verifies the influence of the SAH on extreme precipitation over SWC at a synoptic scale.…”

“…Previous research reported that more extreme precipitation occurs over the Yangtze River Valley with eastward-extended intensified SAH (Y. Chen & Zhai, 2015Y. Chen, Zhai, et al, 2019;Ning et al, 2017).…”

Influence of Large‐Scale Circulation Patterns on Compound Dry and Hot Events in China

“…Precipitation and temperature (or dry and hot events) during summer in China have been shown to be associated with different atmospheric processes. The summer rainfall in western and northern China is closely related to the westerlies while that in eastern China is mainly affected by water vapor transport from the ocean (e.g., the Bay of Bengal, South China Sea, and western Pacific) associated with East Asia Summer Monsoon (EASM), which is related to the Western Pacific Subtropical High (WPSH), East Asian westerly jet (EAWJ), and South Asian High (SAH) (Y. Chen et al., 2019; W. Huang et al., 2015; Linderholm et al., 2011; Q. Sun et al., 2017; W. Wang et al., 2015; W. Wei et al., 2015; L. X. Zhang & Zhou, 2015; Zhu et al., 2015).…”

Mechanisms for regional compound hot extremes in the mid‐lower reaches of the Yangtze River

“…This spatial distribution of ‘positive–negative–positive’ height anomalies largely resembles the mid‐ to high‐latitude sections of the Pacific‐East Asian teleconnection pattern (Huang and Li, 1988), which controls weather and climate in China, but with a more northerly displacement. Such anomalies of large‐scale circulations tend to be relatively stable (Chen et al ., 2019), which is conducive to sustaining high temperatures and, therefore, to producing compound hot extreme events.…”

“…The dispersed energy stimulates disturbances over mid‐lower reaches of the Yangtze River, which subsequently extracts barotropic and baroclinic energy from the background mean flow (the subtropical westerly jet). Regions atop mid‐lower reaches of the Yangtze River are known as a hotspot for disturbance–flow interactions (Chen et al ., 2019). In particular, baroclinic energy conversion is more efficient in maintaining the anomalous anticyclone (disturbances), favouring its persistence through day and night and even over a period of several days.…”