Raindrop size distribution of rainfall system indirectly affected by Typhoon Kong-Rey (2018) passed through the southern parts of Korea

Abstract

The internal structure and microphysical properties of a rainband of Typhoon Kong-Rey (TY), which occurred in 2018, and of the rainfall system indirectly affected by the typhoon (IA) that passed through the southern part of the Korean Peninsula in October 2018, were analyzed by operational S-band weather radars and particle size and velocity (PARSIVEL) disdrometers.The height of maximum intensity (Hc in km) of the IA was located at an elevation of ~ 7.5 km; moreover, in the TY regime, the column maximum (Cmax in dBZ) continuously increased up to 45 dBZ at all observation sites, while Hc decreased to 5 km. The IA showed hardly any increase in temperature during precipitation, differently from the TY.In the TY, the maximum fall velocity (Vmax) of raindrops with maximum diameters (Dmax) comprised between 2 and 3 mm was about 1 m s−1 lower than that of drops during precipitation derived from the typhoon's indirect impact. Convective precipitation in the IA presented the following raindrop size distribution (DSD) characteristics within an interval of 18 h (from 21:00 local standard time (LST) on 4 October to 15:00 LST on 5 October): the mass-weighted mean diameter (Dm) and the logarithmic normalized intercept parameter (logNw) were comprised between 1.3 and 1.5 mm and 3.8–4.3, respectively. However, TY showed large temporal variation within an interval of 15 h: Dm and logNw ranged between 1.2 and 2.9 mm and 2.9–4.6, respectively. Additionally, at rainfall rates (R) of 5–15 mm h−1, the shape parameter (μ) of the IA varied between 4 and 7, while that of the TY between 2 and 10.