Comparative Analysis of Rainfall Droplet Spectra of Typhoon Wipha (201907) in Chongzuo and Fangchenggang, China

We analyzed the structural characteristics and differences in raindrop spectrum at different precipitation stages on the inland leeward side (LSI) and near-coast windward side (WSC) during the impact of typhoon Wipha from August 2 to 3, 2019. We used the raindrop spectrum observation data from Chongzuo National Meteorological Observatory and Fangcheng National Reference Climate Station, combined with rainfall data and radar observation data for the analysis. The results show that typhoon Wipha’s rainfall is mainly contributed by medium and small raindrops, with the proportion of medium raindrops consistently exceeding 70%. The rainfall at LSI is dominated by stratiform clouds with relatively gentle rain intensity, while the rainfall at WSC is characterized by mixed cumulus clouds with considerable rain intensity and severe fluctuations. Raindrop concentration and diameter are significantly larger at WSC than at LSI due to the considerable convective activity and upward velocity. The main factor for the increase in rain intensity at LSI after typhoon landfall is an increase in raindrop diameter. Meanwhile, the increase in rain intensity at WSC after the change from typhoon eye wall to a strong convective spiral rain band is mainly due to an increase in raindrop number concentration. The average mass-weighted mean diameter of typhoon Wipha’s convective precipitation is 1.85 mm, with a logarithmic normalized intercept of 3.95 mm⁻¹ m⁻³. Convective precipitation occurs in the maritime convective region at LSI, while it occurs between maritime and continental convection at WSC.