Evaluation of the assumptions in the steady-state tropical cyclone self-stratified outflow using three-dimensional convection-allowing simulations
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jas-d-19-0033.1.pdf
Description
Published version
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3.87 MB
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Adobe PDF
Checksum (MD5)
3f59c52e84a9243f94f1cbea03cba3b6
Author(s)
Emanuel, Kerry Andrew
Date Issued
September 2019
Journal
Journal of the atmospheric sciences
Publisher
American Meteorological Society
Citation
Tao, Dandan, et al., "Evaluation of the assumptions in the steady-state tropical cyclone self-stratified outflow using three-dimensional convection-allowing simulations." Journal of the atmospheric sciences 76, 9 (September 2019): p. 2995-3009 doi 10.1175/JAS-D-19-0033.1 ©2019 Author(s)
Version
Final published version
Abstract
The criteria and assumptions that were used to derive the steady-state tropical cyclone intensity and structure theory of Emanuel and Rotunno are assessed using three-dimensional convection-allowing simulations using the Weather Research and Forecasting Model. One real-data case of Hurricane Patricia (2015) and two idealized simulations with and without vertical wind shear are examined. In all three simulations, the gradient wind balance is valid in the inner-core region above the boundary layer. The angular momentum M and saturation entropy surfaces s* near the top of the boundary layer, in the outflow region and along the angular momentum surface that passes the low-level radius of maximum wind MRMW are nearly congruent, satisfying the criterion of slantwise moist neutrality in the vicinity of MRMW. The theoretically derived maximum wind magnitude above the boundary layer compares well with the simulated maximum tangential wind and gradient wind using the azimuthally averaged pressure field during the intensification and quasi-steady state of the simulated storms. The Richardson number analysis of the simulated storms shows that small Richardson number (0, Ri #1) exists in the outflow region, related to both large local shear and small static stability. This criticality of the Richardson number indicates the existence of small-scale turbulence in the outflow region. We also show that the stratification of temperature along the M surfaces at the outflow region for steady-state hurricanes is approximately applicable in these three-dimensional simulations, while the radial distribution of gradient wind is qualitatively comparable to the theoretical radial profiles. Some caveats regarding the theory are also discussed. ©2019
MIT Department
Massachusetts Institute of Technology. Program in Atmospheres, Oceans, and Climate
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DOI of Published Version
https://doi.org/10.1175/JAS-D-19-0033.1
