Statistical Characteristics of Raindrop Size Distribution in the South China Monsoon Region (Guangdong Province)

While heavy rainfall frequently takes place in southern China during summer monsoon seasons, quantitative precipitation forecast skills are relatively poor. Therefore, detailed knowledge about the raindrop size distribution (DSD) is useful in improving the quantitative precipitation estimation and forecast. Based on the data during 2018-2022 from 86 stations in a ground-based optical disdrometer measurement network, the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution (N(D)), mass-weighted mean diameter (Dm) and other integral DSD parameters such as radar reflectivity (Z), rainfall rate (R) and liquid water content (LWC). In addition, the effects of geographical locations, weather systems (tropical cyclones, frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered. The results are shown as follows. 1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation, and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution. The relationships between the Z and R for stratiform and convective precipitation are also derived for the province, i.e., Z = 332.34 R1.32 and Z = 366.26 R1.42 which is distinctly different from that of the Next-generation Weather Radar (NEXRAD) Z-R relationship in United States. 2) In the rainy season (April-September), the Dm, R and LWC are larger than those in the dry season (October -March). Moreover the above parameters are larger, especially in mid-May, which is the onset of the South China Sea summer monsoon. 3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dm and a larger normalized intercept parameter (log10Nw), suggestive of maritime-like rainfall. Dm is larger and log10Nw is smaller in the inland area, suggestive of continental-like rainfall. 4) Affected by such weather systems as the tropical cyclone, frontal system and summer monsoon, the DSD shows characteristics with distinct differences. Furthermore, frontal system rainfall tends to present a continental-like rainfall, tropical cyclone rainfall tends to have a maritime-like rainfall, and summer monsoon rainfall characteristic are between maritime-and continental-like cluster (raindrop concentration and diameter are higher than continental cluster and maritime cluster, respectively.)