四川盆地2023年7月11-13日一次持续性大暴雨的物理机制分析OA

A persistent heavy rainfall event occurred in the Sichuan Basin from July 11 to 13,2023,with the maximum cumulative precipitation reaching 656.5 mm,matching the historical record,while the second-high-est cumulative precipitation reached 650.4 mm,breaking the station's observational record.The torrential rain triggered secondary disasters such as flash floods,landslides,and debris flows,resulting in significant losses.This study utilizes dense surface automatic precipitation observation data,Wenjiang sounding data,ERA5 re-analysis data,and FY-4A satellite Brightness Blackbody Temperature(TBB)data to analyze the atmospheric cir-culation background and physical mechanisms of this persistent heavy rainfall event.The results indicate that the South Asian High dominated over Sichuan,while the Western Pacific Subtropical High(WPSH)remained sta-ble on the periphery of Sichuan and upper-level trough moved eastward.Continuous moisture transported from the South China Sea and the Bay of Bengal into Sichuan Basin,which provided ample water vapor for the heavy rainfall.Significant low-level warming and moistening in the western Sichuan Basin enhanced atmospheric insta-bility.The large-scale circulation background created favorable conditions for the occurrence of the persistent heavy rainfall.On the evening of July 10,airflow inertial oscillation generated a low-level jet over the eastern Yunnan-Guizhou Plateau,which enhanced wind speed and moisture advection into the basin.The southeasterly flow,obstructed by the western mountains,induced frontogenesis and moisture convergence ahead of the foot-hills,leading to convective instability.The airflow ascended along the mountain slopes,forming a vertical circu-lation cell over the basin.Orographic lifting and this vertical circulation jointly triggered convection.The persis-tent southeasterly flow,mechanically blocked by the terrain,generated northerly winds in front of mountain,which converged with the southeasterly winds and formed a shear line,promoting organized convective develop-ment.The trumpet-shaped terrain and canyon topography enhanced precipitation.From July 11 to 12,the intensi-fication of WPSH blocked the eastward movement of the southern branch flow and the trough from the plateau.This process,superimposed with the jet stream transport from the eastern Yunnan-Guizhou Plateau,resulted in enhanced convergence over the southern basin,triggering the development of Southwest Vortex.Latent heat re-lease provided thermal condition for the development of the Southwest Vortex,while divergence and vertical transport supplied the dynamic conditions.Guided by the WPSH's peripheral flow and influenced by latent heat-ing,the southwest vortex moved westward,triggering vigorous convective activity.In the early hours of July 13,an eastward-moving upper-level trough guided cold air to move southward along the western basin.The con-vergence of cold and warm air produced intense frontogenesis,triggering precipitation in the pre-frontal warm sector.The intensification of cold air enhanced the development of the cold front and prolonged the lifespan of the Southwest Vortex,resulting in increased rainfall intensity and a significant eastward expansion of the heavy rainfall area.