Fine‐Scale Characteristics and Forming Mechanisms of the Summer Regional Precipitation Events in the Middle and Lower Yangtze River Basin Under Different Dominant Synoptic Patterns

Abstract

Based on the hourly rainfall gauge data from 1,503 stations and ERA5 reanalysis data in summers of 2014–2024, this study reveals the morphology, coverage area (CA), movement and diurnal variation of regional precipitation events (RPEs) in the middle and lower Yangtze River basin (MLYRB) and their forming mechanisms. Results show that RPEs mainly occur under three dominant synoptic patterns: northerly weak‐Meiyu pattern (P1), southerly strong‐Meiyu pattern (P2), and low‐vortex pattern (P3), leading to 52.20%, 37.57%, and 10.23% of total occurrences of RPEs with the rainfall center concentrated in central, southern, and coastal MLYRB, respectively. The RPEs under Meiyu patterns exhibit more elongated morphologies, larger areas and faster movements relative to low‐vortex pattern. The RPEs under P2 are characterized by the weakest intensity but the largest CA among the three synoptic patterns. The diurnal variation of regional mean precipitation amount (RMPA) of RPEs under P1 shows a predominant morning peak at 08:00 Beijing time (BJT) and a secondary afternoon peak at 16:00 BJT, but only one morning (afternoon) peak under P2 (P3). Mechanism analysis indicates the dynamic configuration of much higher deformation and much lower vorticity in the low‐level winds leads to more elongated morphologies of RPEs. The intensity (CA) of RPEs under the Meiyu patterns is mainly governed by the convective instability (frontal convergence). Frontogenesis and stronger moisture convergence at nighttime driven by the acceleration of low‐level ageostrophic winds contribute to the morning peak of RMPA under Meiyu‐type RPEs. Convective instability controls the afternoon peak of RMPA under low‐vortex‐type RPEs.