Characterizing the Kinetic Energetics of Eyewall Axisymmetry and Asymmetries during the Rapid Intensification of an Idealized Tropical Cyclone

Abstract A new formulation of the spectral horizontal kinetic energy (HKE) budget in cylindrical coordinates is developed to study multiscale kinetic energetics of tropical cyclones (TCs). Compared to previous studies, it precisely constructs the energy nonlinear transfer term and comprehensively represents budget contributions from various physical processes. With this formulation, the eyewall axisymmetry and asymmetries during the rapid intensification (RI) of an idealized TC simulation are investigated. The area-averaged eyewall HKE is mainly determined by the following physical processes at the axisymmetric mode: the vertical pressure-gradient work term generates positive contributions nearly at the whole troposphere, with increased HKE redistributed downward by the pressure transverse (radial-vertical) circulation flux divergence and upward by the HKE transverse circulation flux divergence; at the low layer, the nonlinear transfer makes a significant negative contribution, even exceeding that from the vertical pressure-gradient work term, and an additional negative contribution involving axisymmetric–asymmetric coupling is embedded in the HKE transverse circulation flux divergence. Decomposition of the nonlinear transfer reveals that the azimuthal and vertical components produce a weak upscale transfer thereby feeding the eyewall axisymmetric HKE, whereas the radial component produces a much stronger downscale transfer thereby consuming the eyewall axisymmetric HKE. Further analysis shows that the final-formed radius of maximum wind acts as a dynamical boundary separating inner and outer energy transfer regimes. This study provides direct evidence for the net negative role of asymmetries on the axisymmetric kinetic energy during TC intensification.