Radiative Effects on Tropical Cyclone Development in Different Life Stages

Abstract

A tropical cyclone (TC) is a powerful, rotating storm that typically originates over warm tropical oceans and creates strong winds and heavy rain; it is usually a natural disaster with respect to human life and property if it moves over land. This work examines effects of varying radiative forcing on the evolution of two typhoon cases—Typhoon Lionrock (2016) and Typhoon Hagibis (2019)—with the Weather Research and Forecasting (WRF) Model. Hagibis was a rapidly intensifying and quickly moving TC, whereas Lionrock gradually developed and was slow moving. Numerous sensitivity experiments in which shortwave and longwave radiative heating rates were modified were conducted. This study examined latent heating and radiative heating for each experiment. Substantial differences between the sensitivity simulation members indicated that radiative effects can strongly influence TC development. The analysis of diabatic heating sources shows that, before eyewall formation, the differential cooling effect, which indicates that longwave cooling rates between cloud clusters and clear sky differ, can promote low-level inflow and increase relative humidity in the cloud clusters. If the initial relative humidity is low, this effect becomes important because, without differential cooling, the relative humidity remains low, which can promote the generation of cold pools that will prevent cyclone development. After eyewall formation, both the change in temperature lapse rate due to a vertical gradient of radiative heating/cooling and the change in the warm core due to radiative heating/cooling can affect the intensity of a TC; however, the net effect may depend on the magnitude of these influences.