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| Titel |
Optical and geometrical characteristics of cirrus clouds over a Southern European lidar station |
| VerfasserIn |
E. Giannakaki, D. S. Balis, V. Amiridis, S. Kazadzis |
| 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 ; 7, no. 21 ; Nr. 7, no. 21 (2007-11-02), S.5519-5530 |
| Datensatznummer |
250005242
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| Publikation (Nr.) |
 copernicus.org/acp-7-5519-2007.pdf |
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| Zusammenfassung |
| Optical and geometrical characteristics of cirrus clouds over Thessaloniki,
Greece (40.6° N, 22.9° E) have been determined from the analysis
of lidar and radiosonde measurements performed during the period from 2000
to 2006. Cirrus clouds are generally observed in a mid-altitude region
ranging from 8.6 to 13 km, with mid-cloud temperatures in the range from
−65° to −38°C. The cloud thickness generally ranges from 1 to 5
km and 38{%} of the cases studied have thickness between 2 and 3 km. The
retrieval of optical depth and lidar ratio of cirrus clouds is performed
using three different methods, taking into account multiple scattering
effect. The mean optical depth is found to be 0.31±0.24 and the
corresponding mean lidar ratio is 30±17 sr following the scheme of
Klett-Fernald method. Sub-visual, thin and opaque cirrus clouds are observed
at 3%, 57% and 40% of the measured cases, respectively. A
comparison of the results obtained between the three methods shows good
agreement. The multiple scattering errors of the measured effective
extinction coefficients range from 20 to 60%, depending on cloud optical
depth. The temperature and thickness dependencies on optical properties have
also been studied in detail. A maximum mid-cloud depth of ~3.5 km is
found at temperatures around ~−47.5°C, while there is an
indication that optical depth and mean extinction coefficient increases with
increasing mid-cloud temperature. A correlation between optical depth and
thickness was also found. However, no clear dependence of the lidar ratio
values on the cloud temperature and thickness was found. |
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