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| Titel |
An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model |
| VerfasserIn |
M. E. Nicholls, M. T. Montgomery |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 12 ; Nr. 13, no. 12 (2013-06-21), S.5999-6022 |
| Datensatznummer |
250018716
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| Publikation (Nr.) |
 copernicus.org/acp-13-5999-2013.pdf |
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| Zusammenfassung |
Simulations are conducted with a cloud-resolving numerical model to examine
the transformation of a weak incipient mid-level cyclonic vortex into a
tropical cyclone. Results demonstrate that two distinct pathways are
possible and that development along a particular pathway is sensitive to
model physics and initial conditions. One pathway involves a steady increase
of the surface winds to tropical cyclone strength as the radius of maximum
winds gradually decreases. A notable feature of this evolution is the
creation of small-scale lower tropospheric cyclonic vorticity anomalies by
deep convective towers and subsequent merger and convergence by the
low-level secondary circulation. The second pathway also begins with a
strengthening low-level circulation, but eventually a significantly stronger
mid-level circulation develops. Cyclogenesis occurs subsequently when a
small-scale surface concentrated vortex forms abruptly near the center of
the larger-scale circulation. The small-scale vortex is warm core throughout
the troposphere and results in a fall in local surface pressure of a few
millibars. It usually develops rapidly, undergoing a modest growth to form a
small tropical cyclone. Many of the simulated systems approach or reach
tropical cyclone strength prior to development of a prominent mid-level
vortex so that the subsequent formation of a strong small-scale surface
concentrated vortex in these cases could be considered intensification
rather than genesis.
Experiments are performed to investigate the dependence on the inclusion of
the ice phase, radiation, the size and strength of the incipient mid-level
vortex, the amount of moisture present in the initial vortex, and the sea
surface temperature. Notably, as the sea surface temperature is raised, the
likelihood of development along the second pathway is increased. This
appears to be related to an increased production of ice. The sensitivity of
the pathway taken to model physics and initial conditions revealed by these
experiments raise the possibility that the solution to this initial value
problem is near a bifurcation point. Future improvements to model
parameterizations and more accurate observations of the transformation of
disturbances to tropical cyclones should clarify the conditions that favor a
particular pathway when starting from a mid-level vortex. |
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