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Diverse Multiscale Synergies Underlying Persistent Heavy Rainfall Formation During the Meiyu Period Over the Yangtze-Huaihe Region
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DOI：10.1002/joc.70494.png)
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Abstract
En 中文
Persistent heavy rainfall (PHR) during the Meiyu period frequently leads to severe flooding in China. Since the early 2000s, such events have become increasingly common over the Yangtze-Huaihe region, the northernmost sector of China's Meiyu monitoring region, where precipitation exhibits pronounced multiscale characteristics. However, a systematic understanding of how multiscale processes interact to sustain PHR remains lacking. Based on 43 PHR events over the Yangtze-Huaihe region during the Meiyu period of 1961–2020, this study investigates their formation mechanisms from a multiscale perspective and classifies them into three types. Multiscale contribution decomposition reveals that coupling of the background (> 30 days), quasi-biweekly (10–30 days), and synoptic-scale (< 10 days) wind fields with the background moisture field accounts for 93.8% of total precipitation. The events are classified into three types: background-persistent (13 events), synoptic-transient (11 events), and multiscale hybrid (19 events). The background-persistent type is dominated by background circulation with broad, stable moisture transport from the northwestern Pacific. The Meiyu frontal zone is the strongest and most persistent among the three types, which in turn intensifies the upper-level subtropical jet and causes its eastward displacement. The enhanced jet strengthens the secondary circulation at the jet entrance, while the 10–30 days variability gains energy from the basic flow, strengthening the vertical circulation. The synoptic-transient type is dominated by synoptic-scale disturbances (> 54% contribution), with rainfall depending on wave trains propagating along the jet that induce low-level northerly–southwesterly confluence, and the frontal zone shows large variability. The multiscale hybrid type reflects the combined influence of an intensified subtropical jet, a 10–30 days meridional wave train, and intensified synoptic-scale wave trains, with a relatively weak frontal zone. Overall, this study provides a scientific basis for classification-based monitoring and refined forecasting of PHR events over the Yangtze-Huaihe region.
Keywords:
formation mechanism
Meiyu period
multiscale decomposition
objective classification
persistent heavy rainfall
Yangtze-Huaihe region
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