Based on ground automatic station, multi-band weather radar and sounding data, and the fifth generation atmospheric re⁃

analysis ERA5 from the European Centre for Medium-Range Weather Forecasts (ECMWF), the environmental conditions, mesoscale

characteristics and maintenance mechanisms of a rare squall line weather process in Yunnan Province on 7 July 2022 were analyzed. The results show that this squall line occurred within the convergence zone of the continental high and subtropical high, with environmental conditions characterized by strong convective available potential energy, moderate vertical wind shear, and significant intrusion of high-level dry and cold air. Changes in C-band radar reflectivity and radial velocity were closely associated with the occurrence of strong surface winds and hail. The squall line exhibited distinct features, with a pronounced inflow jet near the surface layer, accompanied by velocity ambiguity and gust front characteristics. The hail cells exhibited characteristics such as three-body scattering, midlevel convergence, and storm-top divergence. High spatial and temporal resolution observations from the X-band dual-polarization phased array radar showed that mature hail clouds had a strong reflectivity factor exceeding 55 dBZ. At the same time, a prominent differential reflectivity (ZDR) column was observed near the strong updraft, with vertical extension exceeding the height of the wet-bulb temperature 0 ℃ layer. Dual-polarization parameters further indicated that precipitation occurred during the hailfall process. The analysis found that the long-term maintenance of ground convergence lines, the coexistence of strong updrafts and tilted downdrafts within the storm, and the coupling of low-level convergence with high-level divergence was the main mechanisms sustaining this squall line.

squall line, mesoscale features, dual-polarization quantity, ground convergence line