An investigation into microphysical structure of a squall line in South China observed with a polarimetric radar and a disdrometer

Abstract

The evolution and microphysical structures of a squall line in South China are investigated by combining S-band polarimetric radar datasets with 2D-Video-Disdrometer measurements. The evolution of the squall line is partitioned into formative, intensifying, and mature stages based on convection patterns. Contrary to previous studies, the radar-retrieved drop size distribution in the convective area is found to be maritime-like [small mass-weighted diameter (Dm) and high logarithmic normalized intercept (log10Nw)] in the formative stage and it slowly evolves into a cluster with characteristics in between maritime and continental storms (large Dm and low log10Nw). The leading edge of the convective area is characterized by a differential reflectivity (ZDR) column, with high ZDR values (> 2 dB) extending vertically to over 4 km above the ground. This region contains large raindrops and wet graupel carried by the updraft. Due to warm rain processes (collision and coalescence) and ice rain processes (melting of graupel), log10Nw and liquid water content decrease steadily, but Dm increases from the ground to melting level. The results gained herein appear to have vital implications for understanding the cloud microphysical processes by S-band polarimetric radar and 2D-Video-Disdrometer observations, and provide guidance for cloud microphysics scheme verification in numerical models.