Evolution of Microphysical Structure of a Subtropical Squall Line Observed by a Polarimetric Radar and a Disdrometer during OPACC in Eastern China

The evolution of the microphysical structures of a subtropical squall line observed during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in Eastern China is documented in this paper. The data collected from a C-band, polarimetric Doppler radar (reflectivity Z, differential reflectivity Z_DR, and specific differential phase K_DP) and a disdrometer are used to investigate the variations of microphysical characteristics within the convective region during the formative, intensifying, and mature stages of the squall line. The microphysical characteristics of the squall line are noticeably different among these three stages. When the squall line develops from the formative stage to the mature stage, its radar-derived drop-size distribution (DSD) in the convective region evolves from continental-like convection to more maritime-like convection. Contrary to previous studies, DSD characteristics of a convective line may not be simply locked to a geographical location but varied extensively throughout its life cycle. The polarimetric radar derived liquid water content below the freezing level in the convective region is three times higher than the ice water content above the freezing level. This, in conjunction with a low cloud base (~0.68 km) and a high freezing level (~5 km), indicates a deep warm cloud layer and the dominance of the warm rain process within this squall line.