Distinct Raindrop Size Distributions of Convective Inner- and Outer-Rainband Rain in Typhoon Maria (2018)

Unlike previous studies from a single disdrometer, this study investigates and compares the raindrop size distribution (RSD) characteristics of convective inner-rainband rain (CIR) and convective outer-rainband rain (COR) in Typhoon Maria (2018), simultaneously captured for the first time by a newly established observational network including nine disdrometers in the northeastern Fujian Province of China. It is shown that the radar reflectivity for the CIR increases sharply with decreasing height below the melting layer, whereas it remains nearly unchanged for the COR. This suggests the dominance of collision-coalescence process in the CIR, that is, the collection of small raindrops by larger ones as they fall. Thus, the surface-level CIR generally has far lower concentration of small raindrops and larger mean raindrop diameter than those previously found in the COR. Close to the tropical cyclone (TC) eyewall, it is found for the first time that although the raindrops are relatively large, the raindrop concentration is too low to yield a high rain rate. In contrast, high rain rates are concentrated at a distance of about 1.5-2.5 times the radius of maximum wind from the TC center, where there are appropriate normalized concentrations (log(10)N(w)) and corresponding raindrop diameters. In addition, this study demonstrates differences between the CIR and COR in terms of the RSD evolution with increasing rain rate and the radar reflectivity-rain rate (Z-R) and shape-slope (mu-?) relationships, confirming the existence of different rain microphysics in various rain regions of a TC.