Evolution of Integrated Kinetic Energy and Energy Conversion Efficiency in Tropical Cyclones During Eyewall Replacement Cycles

Abstract

Integrated kinetic energy (IKE) provides a more comprehensive metric of tropical cyclone (TC) destructive potential than maximum wind speed. Previous studies have shown that the eyewall replacement cycle (ERC) is a key process promoting IKE growth, particularly in TCs with distant secondary eyewall formation. Using idealized numerical simulations and the Mean Airflow as Lagrangian Dynamics Approximation (MAFALDA), this study quantifies the respective roles of energy input and energy conversion efficiency in governing TC energetics during ERC. The results show that the increases in surface enthalpy fluxes during ERC are insufficient to explain the substantial rise in kinetic energy (KE) generation. Instead, the dominant factor is a marked improvement in the efficiency with which thermal energy is converted into KE. Before ERC, eyewall‐ and rainband‐associated thermodynamic cycles contribute comparably to total KE production. During ERC, however, vertical mass transport becomes increasingly concentrated within the eyewall, where thermodynamic cycles are inherently more productive and efficient. This redistribution enhances the system‐wide conversion efficiency and accelerates IKE growth. Concurrent structural adjustments, including strengthened eyewall ascent, a deepened inflow layer, and a steeper normalized tangential wind profile, produce a more energetically favorable post‐ERC circulation. Sensitivity experiments further indicate that TCs with more active outer rainbands tend to attain higher efficiency and faster IKE growth, likely because a larger reservoir of rainband‐driven mass transport can be redirected into eyewall overturning during ERC. These results offer an energetics‐based interpretation of the rapid IKE growth often observed in TCs with long‐lived concentric eyewalls.