Abstract:
Based on the hourly precipitation data from automatic weather stations, hourly temperature data from multi-source fusion, high-altitude observation data, meteorological satellite data of FY-4A, X-band dual polarization radar data and ERA5 reanalysis data , the mesoscale characteristics and causes of a warm-sector rainstorm process in Panxi area, southern Sichuan from 20:00 on October 4th, 2022 to 12:00 on October 5th, 2022 is analyzed.The results show that:(1)This process manifested as a β-γ mesoscale convective system on satellite imagery, which has gone through three stages of developing, strengthening and weakening in Zemulong Village area. The mesoscale convective system of rainstorm tilts east from bottom to top, allowing the convective system to maintain and develop for a longer period.(2)The radar echo in Zemulong Village area shows a strip-shaped distribution, the back-propagation and echo training effects is significant. The strong echo nuclei is relatively low, mostly below 4.5km and its individual nuclei weakens rapidly, thus it has a high precipitation efficiency.(3)In this process,the atmosphere is in an unstable state of dryness above and wetness below, with a low level of CCL, LCL, LFC, thus the gas mass does not need to be lifted too strongly to move upward vertically and cause water vapor condensation, then the thunderstorm system can develop rapidly. The weak vertical wind shear also reduces the involvement of unsaturated dry cold air, weakens the entrainment rate and improves the precipitation efficiency. (4)The convergence and cyclonic flow field formed by the blocking effect of the terrain on the northwest edge of Panzhihua are the main factors generating the continuous convection and forming the training effects, thus extreme precipitation occurs in Zemulong Village area. In Guanyintang Village, the southwest low-level jet stream is nearly orthogonal to the northeast mountains, which force the airflow to rise and forming strong precipitation in the low-lying areas in front of the mountain. Due to the southwest low-level jet, convergence of wind speeds caused by terrain, the terrain circulation caused by terrain temperature gradient also promotes the formation of heavy precipitation.