Mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands

Franklin, C, Holland, G and May, P 2006, 'Mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands', Monthly Weather Review, vol. 134, pp. 2649-2669.


Document type: Journal Article
Collection: Journal Articles

Title Mechanisms for the generation of mesoscale vorticity features in tropical cyclone rainbands
Author(s) Franklin, C
Holland, G
May, P
Year 2006
Journal name Monthly Weather Review
Volume number 134
Start page 2649
End page 2669
Total pages 21
Publisher American Meteorological Society
Abstract A high-resolution tropical cyclone model with explicit cloud microphysics has been used to investigate the dynamics and energetics of tropical cyclone rainbands. Analysis of the vorticity interactions that occur within the simulated rainbands demonstrates that couplets of cyclonic-anticyclonic mesovortices can be produced in outer bands. The primary source of this vorticity is the upward tilting of system-generated horizontal vorticity by diabatic heating gradients. The vertical heating gradient in the stratiform cloud also creates a potential vorticity (PV) dipole that accelerates the tangential flow and develops a midlevel jet. The strength of the jet is enhanced by the vortex pair that is oriented radially across the rainband. The Fourier decomposition of the absolute vorticity field shows two counterpropagating vortex Rossby waves associated with the rainband. The wave located on the inner side of the band transports energy toward the vortex center. The outer wave is made up of high wavenumbers and uses the vorticity gradients generated by the rainband. The results support the hypothesis that the heating profile in the stratiform regions of rainbands generates cyclonic PV across the freezing level, which develops a midlevel jet. This mechanism creates a vorticity gradient that enables the propagation of vortex Rossby waves that could allow the rainbands to interact with the mean flow and potentially influence the evolution of the storm by contributing to the symmetric component of vorticity and the development of secondary eyewalls.
Subject Dynamical Systems in Applications
Keyword(s) Hurricane Spiral Bands
Vortex Rossby-Waves
Wind Profiler Observations
Boundary-Layer Structure
Coare Squall Line
Potential-Vorticity
Rear-Inflow
Convective Systems
Part I
Evolution
Copyright notice © 2006 American Meteorological Society.
ISSN 0027-0644
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