Analysis of raindrop size distribution characteristics of typhoon "Chaba" (2203) at different stages from the South China Sea to inland China

To reveal the evolution of microphysical characteristics of precipitation during different development stages of a typhoon, this study utilizes raindrop disdrometer data from the Sansha, Sanya, and Fuchuan stations, corresponding to the developing, intensifying, and weakening stages of Typhoon Chaba (2023), respectively, as it moved from the South China Sea to inland China. A comparative analysis of the raindrop size distribution (DSD) and microphysical mechanisms across the three stages is conducted. The results are as follows. (1) The DSD exhibits significant differences among the different intensity stages. In the developing and intensifying stages, the spectra are unimodal, with the spectral width broadening from 4.25 mm to 6.5 mm. Large raindrops up to 7.5 mm in diameter appear in the intensifying stage, while the spectrum shifts to a bimodal structure in the weakening stage. (2) The microphysical characteristics show stage-dependent variations. The developing stage is characterized by maritime convective features, dominated by warm-rain coalescence. The intensifying stage exhibits both maritime and continental characteristics, with active ice-phase processes, coalescence, and breakup; raindrops with D>3 mm contribute 23.76% to the rainfall intensity. The weakening stage is predominantly continental, with rainfall intensity mainly relying on raindrops of 1–3 mm in diameter. (3) The Gamma function generally provides a good fit to the DSD, but overestimates raindrops with D<1 mm and fails to capture the bimodal structure of precipitation in the weakening stage. The μ–λ relationship differs markedly among the stages, and the corrected Z–R relationship can effectively reduce errors in radar quantitative precipitation estimation.