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| Titel |
Cirrus clouds triggered by radiation, a multiscale phenomenon |
| VerfasserIn |
F. Fusina, P. Spichtinger |
| 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 ; 10, no. 11 ; Nr. 10, no. 11 (2010-06-11), S.5179-5190 |
| Datensatznummer |
250008523
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| Publikation (Nr.) |
 copernicus.org/acp-10-5179-2010.pdf |
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| Zusammenfassung |
In this study, the influence of radiative cooling and small eddies on cirrus
formation is investigated. For this purpose the non-hydrostatic, anelastic
model EULAG is used with a recently developed and validated ice microphysics
scheme (Spichtinger and Gierens, 2009a). Additionally, we implemented a fast
radiative transfer code (Fu et
al., 1998). Using idealized profiles with high
ice supersaturations up to 144% and weakly stable stratifications with
Brunt-Vaisala frequencies down to 0.0018 s−1 within a
supersaturated layer, the influence of radiation on the formation of cirrus
clouds is remarkable. Due to the radiative cooling at the top of the ice
supersaturated layer with cooling rates down to −3.5 K/d, the
stability inside the ice supersaturated layer decreases with time. During
destabilization, small eddies induced by Gaussian temperature fluctuations
start to grow and trigger first nucleation. These first nucleation events
then induce the growth of convective cells due to the radiative
destabilization. The effects of increasing the local relative humidity by
cooling due to radiation and adiabatic lifting lead to the formation of a
cirrus cloud with IWC up to 33 mg/m3 and mean optical depths up
to 0.36. In a more stable environment, radiative cooling is not strong enough
to destabilize the supersaturated layer within 8 h; no nucleation occurs
in this case.
Overall triggering of cirrus clouds via radiation works only if the
supersaturated layer is destabilized by radiative cooling such that small
eddies can grow in amplitude and finally initialize ice nucleation. Both
processes on different scales, small-scale eddies and large-scale radiative
cooling are necessary. |
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