Western North Pacific Typhoons with Concentric Eyewalls
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This study examines the intensity change and moat dynamics of typhoons with concentric eyewalls using passive microwave data and best track data in the western North Pacific between 1997 and 2006. Of the 225 typhoons examined, we have indentified 55 typhoons and 62 cases with concentric eyewalls. The data indicate that approximately 50% of Category 4 and 75% of Category 5 typhoons possessed concentric eyewalls at some point during their life time. While major typhoons are most likely to form the concentric eyewalls, the formation of concentric structure may not be necessarily at the lifetime maximum intensity. Approximately one-third of concentric eyewall cases are formed at the time of maximum intensity A theoretical parameter called filamentation moat width is devised. The filamentation moat width can be computed from the best track typhoon intensity and the passive microwave satellite-estimated inner eyewall radius for each typhoon with concentric eyewalls. The filamentation moat width explains 40% of the variance of the satellite observed moat width in the group with concentric eyewall formation intensity greater than 130 kts. The moat is generally recognized to be heavily influenced by the subsidence forced by the two eyewalls. Our results suggest that the rapid filamentation dynamics may also be contributing to the organizational aspect of the moat in very intense typhoons. The intensity time series in both the concentric and non-concentric composites are studied. Intensity of the concentric typhoons tends to peak at the time of secondary eyewall formation; but the standard model of intensification followed by weakening is valid for only half of the cases. Approximately 74% of the cases intensify 24 h before secondary eyewall formation and approximately 72% of the cases weaken 24 h after formation. The concentric composites have a much slower.
Mon. Wea. Rev. 137, 3758-3770.
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Kuo, H. C.; L. Y. Lin; Chang, C.-P.; R.T. Williams (2004);An important issue in the formation of concentric eyewalls in a tropical cyclone is the development of a symmetric structure from asymmetric convection. We propose, with the aid of a nondivergent barotropic model, that ...
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