Microphysics of Heavy Rain Associated With the Eyewall and Inner Rainbands of Typhoon Meranti (2016)

Abstract

AbstractHeavy rain in a tropical cyclone (TC) tends to occur in its eyewall and inner spiral rainbands. The distinct dynamical and thermodynamical structures between TC eyewall and inner rainbands were argued to be responsible for different rain microphysics by previous studies. Thus, this study investigated the microphysical characteristics of heavy rain (≥10 mm hr−1) associated with the eyewall and inner rainbands of Typhoon Meranti (2016), based on the joint observations of two disdrometers and a dual‐polarization radar (DPR) as well as automatic weather stations in Fujian province of China. The surface disdrometer observation showed that the eyewall rain has a larger mean raindrop diameter and a smaller mean concentration than the inner‐rainband rain. In general agreement with the disdrometer observation, the DPR observation confirmed larger sizes of raindrops near the ground in the eyewall. However, the vertical profiles of polarimetric variables showed larger values almost throughout the atmosphere in the eyewall, namely that more efficient ice‐ and warm‐cloud processes are evident for the production of ice and rain particles. This result looks contradictory to the lower concentration of the eyewall rain than the inner‐rainband rain as measured by surface disdrometers. This is because stronger updrafts observed in the eyewall not only facilitate the production and growth of hydrometeors, but also prevent small raindrops from falling to the ground. Consequently, the surface rain in the eyewall has larger raindrop diameter and lower concentration than that in the inner rainbands, despite a larger number of ice and rain particles in the atmosphere.