Recent Research and Operational Tools for Improved Understanding and Diagnosis of Tropical Cyclone Inner Core Structure

The inner core of a tropical cyclone (TC) is vital for TC energetics and often undergoes dramatic changes. This article provides a review on the understanding and operational practices of the structural changes in the TC inner core, mainly focusing on recent literature and activities. The inner core structure of a TC is generally described as an axisymmetric vortex in the vicinity of a hydrostatic and gradient wind-balanced state. However, this sche-matic can sometimes be oversimplified. Recent studies have documented small-scale features of the inner core, structural changes in TC rapid intensification, secondary eyewall formation, and eyewall replacement cycles using observational data, and idealized and sophisticated models. In line with the progress in understanding the inner core structure, several operational agencies have recently analyzed TC structural changes using their subjective analyses or diagnostic tools, contributing to disaster prevention. We also discuss potential impacts of climate change on the inner core structure, for which further work is required to reach a solid conclusion.