Microphysical Characteristics of a Northeast China Cold Vortex Squall Line and Its Contrast with Meiyu-Front Precipitation: A Polarimetric Radar and Disdrometer Study

Extreme precipitation in Northeast China is often influenced by the Northeast China Cold Vortex (NCCV), yet the microphysical processes operating within such systems remain poorly characterized. In this study, we investigate an NCCV-associated squall line that occurred over Liaoning Province by integrating S-band polarimetric radar with ground-based disdrometer measurements. The analysis focuses on raindrop size distribution (DSD) characteristics and three-dimensional microphysical structure in both convective and stratiform regimes. A comparison is also performed between this squall line and a Mei-yu frontal event, with emphasis on DSD differences and the underlying mechanisms. Observations indicate that convective precipitation within the NCCV squall line exhibits a continental-type DSD, marked by relatively low drop concentrations but larger raindrops when compared with other heavy rainfall regimes across China. In contrast, the Mei-yu frontal convection displays a transitional DSD, falling between maritime and continental types, characterized by smaller but more numerous raindrops. Vertically, the mature squall line features well-defined columns of differential reflectivity (ZDR) and specific differential phase (KDP) extending above the melting level within convective regions, signaling vigorous riming growth of graupel and hail sustained by strong updrafts. Meanwhile, the stratiform region is dominated by ice crystals and aggregates, formed primarily through deposition and aggregation. As these ice-phase particles melt, subsequent collision-coalescence and evaporation-driven size sorting collectively shape the observed surface DSD, which is large in size yet sparse in number. In contrast to the Mei-yu frontal system, the NCCV squall line develops under drier and more unstable atmospheric conditions that favor deep convection and active ice-phase microphysics. The Mei-yu environment, by contrast, is relatively moist and stable, promoting shallower convection where warm-rain processes prevail. These differences in thermodynamic settings directly account for the distinct DSD signatures observed between the two systems. Future research involving multi-case analyses with integrated observational datasets will be essential to quantitatively assess how environmental and aerosol factors modulate these heavy precipitation events.