Diurnal Cycle of Extreme Rainfall Over the Dabie Mountain in Summer Under Typical Synoptic Patterns and Associated Mechanisms

Abstract Summer extreme rainfall frequently occurs in the Dabie Mountain (DM). The combined effects of synoptic patterns and local topography on the spatiotemporal variations of extreme rainfall in the summers from 2008 to 2020 have been investigated using an objective classification method. Results show that extreme rainfall in the DM mainly occurs under two typical synoptic patterns (P1 and P2). In the lower troposphere, the P1 type is characterized by southwesterly (easterly) winds south (north) to the DM, while the P2 type features southwesterly winds over the DM. These differences arise from the varying position of the Meiyu front. Under both types, extreme rainfall intensity reaches its diurnal maximum at around 09:00 local solar time (LST) because the low‐level southwesterly ageostrophic wind peaks in the early morning induced by inertial oscillation. The southwesterly ageostrophic winds bring abundant water vapor into the DM, resulting in the extreme rainfall along the windward slope. Extreme rainfall intensity decreases rapidly after 09:00 LST under the P2 type but sustains its maximum level for several hours under the P1 type. Two factors contribute to the prolonged high extreme rainfall intensity under the P1 type. One is the convergence between southwesterly and northeasterly ageostrophic flows over the DM. The other is the strengthening of the low‐level vortice over the DM from late morning to early afternoon. Overall, the synoptic patterns influence extreme rainfall by regulating the low‐level ageostrophic winds and the interactions between multi‐scale systems and the DM.