Eyewall asymmetries and their contributions to the intensification of an idealized tropical cyclone translating in uniform flow

Abstract

Abstract Scale-dependent processes within the tropical cyclone (TC) eyewall and their contributions to intensification are examined in an idealized simulation of a TC translating in uniform environmental flow. The TC circulation is partitioned into axisymmetric, low-wavenumber (m = 1–3), and high-wavenumber (m > 3) categories, and scale-dependent contributions to the intensification process are quantified through the azimuthal-mean relative (vertical) vorticity and tangential momentum budgets. To further account for the interdependent relationship between the axisymmetric vortex structure and eyewall asymmetries, the analyses are subdivided into three periods—early, middle, and late—that represent the approximate quartiles of the full intensification period prior to the TC attaining its maximum intensity. The asymmetries become concentrated among lower azimuthal wavenumbers during the intensification process and are persistently distributed among a broader range of azimuthal scales at higher altitudes. The scale-dependent budgets demonstrate that the axisymmetric and asymmetric processes generally oppose each other during TC intensification. The axisymmetric processes are mostly characterized by a radial spin-up dipole pattern, with a tangential momentum spin-up tendency concentrated along the radius of maximum tangential winds (RMW) and a spin-down tendency concentrated radially inward of the RMW. The asymmetric processes are mostly characterized by an opposing spin-down dipole pattern that is slightly weaker in magnitude. The most salient exception occurs from high-wavenumber processes contributing to a relatively modest, net spin-up along the RMW between ~2–4 km altitude. Given that the maximum tangential winds persistently reside below 2-km altitude, eyewall asymmetries are primarily found to impede TC intensification.