Spatial and temporal variation of raindrop size distribution in Great Britain

Raindrop size distributions (DSDs) play a key role in revealing the underlying physical processes of rainfall. This study investigates the characteristics of the DSDs in Great Britain (GB) using data collected from eleven Thies laser precipitation monitors (LPMs) between 2017 and 2019. Around one million one-minute raindrop samples were fitted to a normalized gamma drop distribution model. This study examines the DSD characteristics from both temporal (seasons) and spatial (geography and topography) perspectives, considering different rain types(stratiform and convective) and rain rate clusters. The results indicate that the average mass-weighted mean diameter〈<i>D_m</i>〉 and the average normalized intercept parameter log₁₀〈<i>N_w</i>〉 are influenced by geographical and atmospheric conditions. The 〈<i>D_m</i>〉 tends to be lower and log₁₀〈<i>N_w</i>〉 is higher in the western and hilly regions, with the opposite pattern observed over the eastern plain of GB. Both parameters are strongly correlated with rain rate. Compared to subtropical/tropical regions, stratiform rain in GB exhibits smaller 〈<i>D_m</i>〉 and larger log₁₀〈<i>N_w</i>〉,while the characteristics of convective rain align with the maritime-like cluster. Significant differences in 〈<i>D_m</i>〉are observed between stratiform (0.78–1.00 mm) and convective (1.30–1.74 mm) rain, with both showing a significant negative linear correlation with log10〈<i>N_w</i>〉. Moreover, extreme convective events show distinct seasonality, with larger <i>D_m</i> and lower log₁₀(<i>N_w</i>) during the warm season. Furthermore, a bimodal distribution is observed for log₁₀(<i>N_w</i>) in light rain events over western and hilly regions, highlighting the complexity of microphysical processes associated with small raindrops. The characteristics of DSDs observed in this study provide valuable insights for future investigations into GB’s precipitation formation and quantitative precipitation estimation using weather radar.