Evolution of thermodynamic and microphysical structures of a meso-β-scale convection system responsible for extreme rainfall over North China

Extreme rainfall (ER) produced by convective storms moving from mountains to plain areas in North China has long been a great challenge in short-term forecasting, since the production of rainfall is closely related to the fine structure of convection. This type of ER event stroke the northern Beijing on 26 July 2025, causing widespread concern of the community. Based on multi-source observations and convectionpermitting simulation, this study attempts to reveal the thermodynamic and microphysical structures in the meso-β-scale convection system (MCS-k) which produced the ER. Observational facts show that the weakening of cold outflow together with the southeast wind in warm sector hindered the movement of MCS-k after going downhill, and the more abundant water vapor and stronger convective instability in plain areas led to its back-building development. The content of liquid water significantly increased, and more large raindrops were produced by the coalescence, indicating more intense warm-rain processes. Simulation experiments show that direct contribution of the warm-rain processes dominated the production of ER since they provided 77.8% of the increase in sedimentation of rainwater. Although the ice-phase 2 processes were intensified, most of the snow and graupel were transported out of the convection and did not directly contribute to the production of ER. Meanwhile, the latent heating of ice-phase processes played an important role. The sensitivity experiment dismissing the latent heat from production of snow and graupel significantly weakens the ascending motion and production of rainwater in MCS-k, which decreases the 6-h rainfall amount in northern Beijing by 44%.