Microphysical characteristics of frontal and warm-sector rainbands coexisting in Southern China

Abstract:

Heavy rainfall over Southern China is often characterized by the coexistence of double rainbands: one is an inland frontal rainband (FR) and the other is a coastal warm-sector rainband (WR). Previous studies have shown that the double rainbands exhibit different features in both dynamics and thermodynamics. However, their differences in microphysical properties has not been well understood. In the present study, S-band dual-polarization radar observations are utilized to investigate the differences in microphysical characteristic between the FR and WR in an event occurred on 12 June 2019 in Southern China. Convection embedded in the WR has larger horizontal radar reflectivity Z_H than that in the FR. Besides, the WR convection features greater differential reflectivity (Z_DR) below the freezing level but smaller Z_DR above the freezing level compared to the FR convection. Further analysis indicates that stronger updrafts in the WR convection transport more droplets to the layer above the freezing level, which promotes the production of graupel via riming and large raindrops melting from graupel particles. These microphysical processes thus result in larger Z_DR below the freezing level in the WR convection, and its rain size distributions (RSDs) partly exhibit continental-like convection characteristic. In contrast, ice-based microphysical processes are less active in the FR convection with more irregular oriented ice crystals remaining in the upper level, which leads to larger Z_DR above the freezing level. RSDs produced by the FR convection show marine-like convection characteristic.