Technical note: On the ice microphysics of isolated thunderstorms and non-thunderstorms in southern China – a radar polarimetric perspective

Abstract. Determining whether a cloud will evolve into a thunderstorm is beneficial for understanding thunderstorm formation and also important for ensuring the safety of society. However, a clear understanding of the microphysics of clouds in terms of the occurrence of lightning activity has not been attained. Vast field observations and laboratory experiments indicate that graupel, which is rimed ice, is a vital hydrometeor for lightning generation and is the foundation of riming electrification. In this study, polarimetric radar and lightning observations are used to compare the ice microphysics associated with graupel between 57 isolated thunderstorms and 39 isolated non-thunderstorms, and the differences in radar parameters are quantified. Our results for the occurrence of lightning activity in clouds revealed the following results: (1) the maximum difference in graupel volume at the −10 °C isotherm height between thunderstorms and non-thunderstorms reached approximately 7.6 km3; (2) the graupel particles approached spherical shapes, with a mean differential reflectivity (ZDR) value of 0.3 dB, which likely indicated that heavily rimed graupel was present; (3) the median values of horizontal reflectivity (ZH) or ZDR at positions where the source initiation and channel of the first lightning flashes were nearly 31 dBZ or 0 dB; and (4) 98.2 % of the thunderstorms were equipped with a ZDR column, and the mean depth was ∼ 2.5 km. Our study deepens our understanding of lighting physics and thunderstorm formation.