Why Do Model Tropical Cyclones Grow Progressively in Size and Decay in Intensity after Reaching Maturity?

The long-term behavior of tropical cyclones in the prototype problem for cyclone intensification on an f plane is examined using a nonhydrostatic, three-dimensional numerical model. After reaching a mature intensity, the model storms progressively decay while both the inner-core size, characterized...

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Bibliographic Details
Published in:Journal of the atmospheric sciences 2016-02, Vol.73 (2), p.487-503
Main Authors: Kilroy, Gerard, Smith, Roger K, Montgomery, Michael T
Format: Article
Language:English
Subjects:
Amplification
Atmospherics
Boundary layer
Boundary layers
Circulation
Cyclones
Decay
Heating
Hurricanes
Mathematical models
Meteorology
Ocean circulation
Reduction
Storms
Tropical cyclones
Troposphere
Typhoons
Velocity
Vertical distribution
Vortices
Wind
Wind speed
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Summary:The long-term behavior of tropical cyclones in the prototype problem for cyclone intensification on an f plane is examined using a nonhydrostatic, three-dimensional numerical model. After reaching a mature intensity, the model storms progressively decay while both the inner-core size, characterized by the radius of the eyewall, and the size of the outer circulation-measured, for example, by the radius of the gale-force winds-progressively increase. This behavior is explained in terms of a boundary layer control mechanism in which the expansion of the swirling wind in the lower troposphere leads through boundary layer dynamics to an increase in the radii of forced eyewall ascent as well as to a reduction in the maximum tangential wind speed in the layer. These changes are accompanied by changes in the radial and vertical distribution of diabatic heating. As long as the aggregate effects of inner-core convection, characterized by the distribution of diabatic heating, are able to draw absolute angular momentum surfaces inward, the outer circulation will continue to expand. The quantitative effects of latitude on the foregoing processes are investigated also. The study provides new insight into the factors controlling the evolution of the size and intensity of a tropical cyclone. It provides also a plausible, and arguably simpler, explanation for the expansion of the inner core of Hurricane Isabel (2003) and Typhoon Megi (2010) than that given previously.
ISSN:0022-4928
1520-0469
DOI:10.1175/JAS-D-15-0157.1