Microphysical Characteristics of Tropical Cyclone Choiwan (2021) Outer Rainbands Derived From Polarimetric Radar Observations on a Research Vessel

Microphysical characteristics of tropical cyclones (TCs) over the open ocean remain elusive due to observation constraints. In this study, dual-polarization observations derived from a ship-borne C-band polarimetric radar are utilized to investigate the microphysical characteristics of an outer rainband associated with TC Choiwan during its evolution over the South China Sea from 0500 to 1300 UTC on 3 June 2021. Based on TC and convection intensity, the eight-hour period is categorized into three stages with distinct microphysical features: pre-mature, mature and post-mature. During the mature stage, both ice-phase and warm rain processes are active, resulting in a distribution pattern where most convective cells (CCs) contain high concentrations of small raindrops with a few exhibiting extremely large raindrops, and making raindrop size distributions (DSDs) fall between “continental-like” and “maritime-like”. In the pre-mature and post-mature stages, ice-phase processes predominantly govern the growth of raindrops, with CCs displaying “continental-like” DSD characteristics.