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| Titel |
Convective formation of pileus cloud near the tropopause |
| VerfasserIn |
T. J. Garrett, J. Dean-Day, C. Liu, B. Barnett, G. Mace, D. Baumgardner, C. Webster, T. Bui, W. Read, P. Minnis |
| 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 ; 6, no. 5 ; Nr. 6, no. 5 (2006-04-19), S.1185-1200 |
| Datensatznummer |
250003723
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| Publikation (Nr.) |
 copernicus.org/acp-6-1185-2006.pdf |
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| Zusammenfassung |
| Pileus clouds form where humid, vertically stratified air is mechanically
displaced ahead of rising convection. This paper describes convective
formation of pileus cloud in the tropopause transition layer (TTL), and
explores a possible link to the formation of long-lasting cirrus at cold
temperatures. The study examines in detail in-situ measurements from off the
coast of Honduras during the July 2002 CRYSTAL-FACE experiment that showed an
example of TTL cirrus associated with, and penetrated by, deep convection.
The TTL cirrus was enriched with total water compared to its surroundings,
but was composed of extremely small ice crystals with effective radii between
2 and 4 μm. Through gravity wave analysis, and intercomparison of
measured and simulated cloud microphysics, it is argued that the TTL cirrus
originated neither from convectively-forced gravity wave motions nor
environmental mixing alone. Rather, it is hypothesized that a combination of
these two processes was involved in which, first, a pulse of convection
forced pileus cloud to form from TTL air; second, the pileus layer was
punctured by the convective pulse and received larger ice crystals through
interfacial mixing; third, the addition of this condensate inhibited
evaporation of the original pileus ice crystals where a convectively forced
gravity wave entered its warm phase; fourth, through successive pulses of
convection, a sheet of TTL cirrus formed. While the general incidence and
longevity of pileus cloud remains unknown, in-situ measurements, and
satellite-based Microwave Limb Sounder retrievals, suggest that much of the
tropical TTL is sufficiently humid to be susceptible to its formation. Where
these clouds form and persist, there is potential for an irreversible
repartition from water vapor to ice at cold temperatures. |
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