Mechanisms for a record‐breaking rainfall event over the eastern periphery of the Tibetan plateau: Dominant synoptic systems and cloud microphysical processes

Abstract A record‐breaking rainfall event (RBRE) with a maximum daily rainfall amount of 428.2 mm occurred in the eastern periphery of the Tibetan plateau (EPTP) on 10 August 2020. However, the mesoscale and cloud microphysical processes underlying such RBREs in regions with complex terrain remain unclear. Based on multisource observations and a convective‐permitting model, the dominant synoptic systems and key cloud microphysical processes associated with this RBRE are examined. The results reveal that the RBRE was primarily driven by the synergistic interaction between the Tibetan Plateau vortex (TPV) to the northwest of the EPTP region and the low‐level jet (LLJ) to the southeast. This interaction promoted local vorticity growth, leading to the formation of a meso‐β‐scale convective vortex accompanied by enhanced vertical motion, which drove the rapid development of the rainstorm. Further analysis demonstrated the vertically distinct mechanisms in vorticity enhancement: positive vorticity advected by the eastward‐moving TPV dominantly contributed to the vorticity above 500 hPa, and LLJ‐induced inhomogeneous diabatic heating prompted vorticity enhancement below 700 hPa. Latent heat budget analysis showed that diabatic heating in the upper levels was primarily driven by the deposition of water vapor into snow, while in the mid‐to‐lower atmosphere, it was mainly due to the condensation of water vapor into cloud water. The growth of rainwater particles primarily resulted from cloud water collection and snow melting, demonstrating the active roles of both collision–coalescence and ice‐phase microphysical processes. The results provide new insights into the physical mechanisms of heavy rainfall events in the EPTP region.