Publication:
Departures from axisymmetric balance dynamics during secondary eyewall formation

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Authors
Abarca, Sergio F.
Montgomery, Michael T.
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Date of Issue
2014-10
Date
Publisher
American Meteorological Society
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Abstract
Departures from axisymmetric balance dynamics are quantified during a case of secondary eyewall formation. The case occurred in a three-dimensional mesoscale convection-permitting numerical simulation of a tropical cyclone, integrated from an initial weak mesoscale vortex in an idealized quiescent environment. The simulation exhibits a canonical eyewall replacement cycle. Departures from balance dynamics are quantified by comparing the azimuthally averaged secondary circulation and corresponding tangential wind tendencies of the mesoscale integration with those diagnosed as the axisymmetric balanced response of a vortex subject to diabatic and tangential momentum forcing. Balance dynamics is defined here, following the tropical cyclone literature, as those processes that maintain a vortex in axisymmetric thermal wind balance. The dynamical and thermodynamical fields needed to characterize the background vortex for the Sawyer-Eliassen inversion are obtained by azimuthally averaging the relevant quantities in the mesoscale integration and by computing their corresponding balanced fields. Substantial differences between azimuthal averages and their homologous balance-derived fields are found in the boundary layer. These differences illustrate the inappropriateness of the balance assumption in this region of the vortex (where the secondary eyewall tangential wind maximum emerges). Although the balance model does broadly capture the sense of the forced transverse (overturning) circulation, the balance model is shown to significantly underestimate the inflow in the boundary layer. This difference translates to unexpected qualitative differences in the tangential wind tendency. The main finding is that balance dynamics does not capture the tangential wind spinup during the simulated secondary eyewall formation event.
Type
Article
Description
The article of record as published may be found at http://dx.doi.org/10.10.1175/JAS-D-14-0018.1
Series/Report No
Department
Meteorology
Organization
Naval Postgraduate School (U.S.)
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Format
18 p.
Citation
S.F. Abarca, M.T. Montgomery, "Departures from axisymmetric balance dynamics during secondary eyewall formation," Journal of the Atmospheric Sciences, v. 71 (October 2014), pp.3723-3738
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.
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