Characteristics of the Rain Drop Size Distribution in Two Squall Lines Measured By Two-Dimensional Video Disdrometer at Guangdong

Raindrop size distributions (DSDs) are an important characteristic of microphysical processes. Temporal evolution and spatial variations of the DSDs in two squall lines (Typical squall line and Typhoon Squall Line) are analyzed based on a two-dimensional video disdrometer (2DVD) from South China Cloud Physics and Heavy Rainfall Field Experiment Base. Results show that the variation of radar reflectivity and concentration of raindrop are nearly the same as precipitation rate. Moreover, the variation of the slope λ is connected with the μ shape parameter. In typical squall line, the enhanced changes of rainfall and radar reflective are related to number concentration of raindrop and the concentration of medium and large sized raindrops, while they are mainly related to number concentration in Typhoon squall line. According to the temporal variation of precipitation rate, the precipitations are divided into the convective and stratiform rain. For convective rain, where R is increasing, the DSDs are characterized by higher and lower number concentrations of large and small sized drops, higher radar reflective, broader raindrop size spectrum and gentler λ and μ in two squall lines. In contrast, where R is decreasing, the DSDs are characterized by lower and higher number concentrations of large and small sized drops, lower radar reflective, narrower raindrop size spectrum and steeper λ and μ in two squall lines. In typical squall line, the DSDs are characterized by “continental-like’’ clusters with higher concentration of medium sized drops for convective rain because of stronger atmospheric ascending motion and a higher concentration of small drops in stratiform rain. In typhoon squall line, the DSDs are characterized by narrower and smoother spectra, a higher concentration of midsize and small drops, respectively, also “maritime-like” and “continental-like’’ clusters for convective rain.