Microphysical Characteristics of Frontal and Warm Sector Heavy Rainfall Over South China During the Pre‐Summer Rainy Season

Abstract Two distinct types of precipitation—frontal heavy rainfall (FR) and warm sector heavy rainfall (WR)—frequently occur in South China during early summer (April–June). FR and WR are produced within different environmental conditions, but their microphysical differences and the possible underlying causes remain unclear. We use polarimetric radar observations and the ERA5 reanalysis data to investigate the microphysical properties of convective cells (CCs) in FR and WR. Overall, both frontal and warm sector CCs produce maritime‐type convective rain, but FR events exhibit stronger convection intensity, larger raindrop sizes, and higher rain rates than WR events. The larger reflectivity above the freezing level and the higher occurrence frequency of large‐sized graupel in FR suggest more active riming process, which might be partly attributed to its stronger dynamic conditions (i.e., larger 0–3 km storm relative helicity and stronger 0–6 km shear) and higher supercooled liquid water content. Collisional coalescence serves as the primary growth mechanism for raindrops in both types of CCs below the melting layer. However, in frontal CCs having the top 10 percentile mass‐weighted mean raindrop diameters oversized raindrops undergo breakup. The ratio of ice and liquid water contents indicates that warm rain processes play a key role in the formation of rainfall particularly in WR. These findings provide new insights into the microphysical characteristics of heavy rainfall in the tropical monsoon region of South China.