Abstract
Persistent heavy rainfall events (PHREs) over the Yangtze–Huaihe River Valley (YHRV) during 1981–2020 are classified into three types (type-A, type-B and type-C) according to pattern correlation. The characteristics of the synoptic systems for the PHREs and their possible development mechanisms are investigated. The anomalous cyclonic disturbance over the southern part of the YHRV during type-A events is primarily maintained and intensified by the propagation of Rossby wave energy originating from the northeast Atlantic in the mid–upper troposphere and the northward propagation of Rossby wave packets from the western Pacific in the mid–lower troposphere. The zonal propagation of Rossby wave packets and the northward propagation of Rossby wave packets during type-B events are more coherent than those for type-A events, which induces eastward propagation of stronger anomaly centers of geopotential height from the northeast Atlantic Ocean to the YHRV and a meridional anomaly in geopotential height over the Asian continent. Type-C events have “two ridges and one trough” in the high latitudes of the Eurasian continent, but the anomalous intensity of the western Pacific subtropical high (WPSH) and the trough of the YHRV region are weaker than those for type-A and type-B events. The composite synoptic circulation of four PHREs in 2020 is basically consistent with that of the corresponding PHRE type. The location of the South Asian high (SAH) in three of the PHREs in 2020 moves eastward as in the composite of the three types, but the position of the WPSH of the four PHREs is clearly westward and northward. Two water vapor conveyor belts and two cold air conveyor belts are tracked during the four PHREs in 2020, but the water vapor path from the western Pacific is not seen, which may be caused by the westward extension of the WPSH.
Highlights
In recent years, the duration of persistent heavy rainfall events (PHREs) in many regions has shown a notable increasing trend (Trenberth et al, 2003; Du et al, 2019)
We found that the criteria worked well for both datasets, that chosen events from both datasets during 1981–2011 were roughly the same, and that most of the identified non-typhoon PHREs in the Yangtze–Huaihe River Valley (YHRV) were consistent with the events in other studies (Chen and Zhai, 2013)
After eliminating the cases with correlation coefficient < |0.3|, a total of 39 PHREs were classified into three types (Table 1): rainbands in the southern part of the YHRV, rainbands in the northern part of the YHRV, and rainbands along the Yangtze River Valley
Summary
The duration of persistent heavy rainfall events (PHREs) in many regions has shown a notable increasing trend (Trenberth et al, 2003; Du et al, 2019). The increased precipitation frequency for regions around the Bohai Sea Rim and South China is largely caused by the prolonged duration of rainfall events (Li et al, 2016). Some specific PHREs have been investigated in terms of the climatology and synoptic weather circulations, e.g., the PHREs during the mei-yu season of 1991, 1998, and 1999 in the YHRV (Ding, 1993; Ding and Sun, 2001; Tao et al, 2001) These studies indicated that PHREs often occur in a quasi-stationary pattern, when the synoptic scale and mesoscale systems coexist in the same area or propagate along the same paths, resulting in significant cumulative rainfall (Ding, 1993).
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