Research on raindrop size distributions of strong precipitation events during the South China pre-flood season

To study the microphysical characteristics of warm-sector rainfall (WR) and frontal rainfall (FR) during the South China pre-flood season, the two-dimensional video raindrop spectrometer (2DVD) data, automatic station precipitation data, and ERA5 reanalysis data from four rainfall events were investigated in this study. The raindrop size distribution (DSD) parameters, the shape factor and slope factor (μ-Λ), and the relationship between radar reflectivity factor and rain intensity (Z-R) of FR events on June 17, 2017, and April 6, 2023, and WR events on June 22, 2017 and May 11, 2022 were analyzed. The results are as follows. (1) In both FR and WR events, convective precipitation dominates, which has a high concentration of each raindrop size (especially a diameter smaller than 1 mm) and a large raindrop diameter. Both the occurrence probability and precipitation contribution ratio of convective precipitation in WR events are higher than those in FR events. (2) During the convective development stage of precipitation in WR and FR events, the increase of rain intensity R usually lags behind that of radar reflectivity factor Z. The extreme values of R, mass-weighted diameter Dm, and generalized intercept parameter lgNw in WR are much larger than those in FR. (3) The value of Dm and lgNw is larger in WR events, showing that the distribution of convective precipitation in WR events is relatively dispersed, compared to the smaller Dm and lgNw in the stratiform precipitation of FR events. (4) The μ-Λ relationships and Z-R relationships of FR and WR events differ significantly. Also, the Z-R relationships in this study are different from the classical Z-R relationship of continental convective precipitation.