A transition mechanism for the spontaneous axisymmetric intensification of tropical cyclones

Yoshiaki Miyamoto, Tetsuya Takemi

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

A mechanism for the transition of tropical cyclones (TCs) to the spontaneous rapid intensification (RI) phase is proposed based on numerical results of a three-dimensional full-physics model. The intensification phase of the simulated TC is divided into three subphases according to the rate of intensification: 1) a slowly intensifying phase, 2) an RI phase, and 3) an adjustment phase toward the quasi-steady state. The evolution of a TC vortex is diagnosed by the energy budget analysis and the degree of axisymmetric structure of the TC vortex, and the simulated TC is determined to be axisymmetrized 12 h before the onset of RI. It is found that equivalent potential temperature θe in the lowest layer suddenly increases inside the radius of maximum azimuthally averaged horizontal wind rma after the TC becomes nearly axisymmetric. Forward trajectory analyses revealed that the enhanced convective instability in the TC core region where the eyewall subsequently forms results from the increased inertial stability of the TC core after the axisymmetrization. Since fluid parcels remain longer inside rma, owing to the increased inertial stability, the parcels obtain more enthalpy from the underlying ocean. As a result, low-level θe and hence convective available potential energy (CAPE) increase. Under the condition with increased CAPE, the eyewall is intensified and the secondary circulation is enhanced, leading to the increased convergence of low-level inflow; this process is considered to be the trigger of RI. Once the eyewall forms, the simulated TC starts its RI.

Original languageEnglish
Pages (from-to)112-129
Number of pages18
JournalJournal of the Atmospheric Sciences
Volume70
Issue number1
DOIs
Publication statusPublished - 2013 Jan 1
Externally publishedYes

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tropical cyclone
potential energy
vortex
potential temperature
energy budget
enthalpy
inflow
physics
trajectory
fluid
ocean

ASJC Scopus subject areas

  • Atmospheric Science

Cite this

A transition mechanism for the spontaneous axisymmetric intensification of tropical cyclones. / Miyamoto, Yoshiaki; Takemi, Tetsuya.

In: Journal of the Atmospheric Sciences, Vol. 70, No. 1, 01.01.2013, p. 112-129.

Research output: Contribution to journalArticle

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