Differences in the raindrop size distributions of pre-monsoon thunderstorms and tropical cyclones observed over eastern India

Investigations on the raindrop size distributions (RSDs) are essential for understanding the dynamical and microphysical processes contributing to precipitation. Empirical relationships derived from RSD parameters, like radar reflectivity–rainfall rate (Z–R), mass-weighted mean diameter–rainfall rate (D_m–R), shape–slope (μ–Ʌ), and normalized intercept parameter–rainfall rate (log₁₀N_w–R) relationships, can enhance the rainfall estimation, and cloud modeling simulations. In the present study, four years (2018–2021) measurements of a Laser Precipitation Monitor (LPM; Thies) disdrometer installed at the National Institute of Technology Rourkela, India, are used to investigate the RSD characteristics of thunderstorms (TSs) and tropical cyclones (TCs) observed during pre-monsoon (March–May) season. Along with the disdrometer data, auxiliary parameters like convective available potential energy (CAPE), convective inhibition (CIN), total column water vapor (WV), vertical profiles of temperature (T) and relative humidity (RH) from reanalysis data sets of ECMWF (European Centre for Medium-Range Weather Forecasts) fifth-generation reanalysis (ERA5) are also used in this study. TCs have dominant small-sized raindrops, whereas moderate and large-sized raindrops predominate in TSs. Diurnal variation of RSD indicates that raindrop sizes during TCs are limited to 4.5 mm. The mean values of R, Z, D_m, μ, and liquid water content (W) are maximum during the TSs and the normalized intercept parameter (log₁₀N_w) and slope parameter (Ʌ) are maximized during the TCs. The average RSD indicated significant variations between TSs and TCs precipitation with a significant difference in Z–R, D_m–R, μ–Ʌ, log₁₀N_w–R relationships. The Z–R relationships during the TSs and TCs are Z = 543.22R^1.46 and Z = 291.3R^1.31, respectively. The diurnal variations in Z–R coefficient ‘A' and exponent ‘b’ values are associated with sizeable diurnal variations of CAPE and CIN.