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| Titel |
A variational approach for retrieving ice cloud properties from infrared measurements: application in the context of two IIR validation campaigns |
| VerfasserIn |
O. Sourdeval, L. C. Labonnote, G. Brogniez, O. Jourdan, J. Pelon, A. Garnier |
| 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. 16 ; Nr. 13, no. 16 (2013-08-21), S.8229-8244 |
| Datensatznummer |
250085638
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| Publikation (Nr.) |
 copernicus.org/acp-13-8229-2013.pdf |
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| Zusammenfassung |
| Cirrus are cloud types that are recognized to have a strong impact on the
Earth-atmosphere radiation balance. This impact is however still poorly
understood, due to the difficulties in describing the large variability of
their properties in global climate models. Consequently, numerous airborne
and space-borne missions have been dedicated to their study in the last
decades. The satellite constellation A-Train has for instance proven to be
particularly helpful for the study of cirrus. More particularly, the Infrared
Imaging Radiometer (IIR) carried onboard the Cloud-Aerosol Lidar and Infrared
Pathfinder Satellite Observation (CALIPSO) satellite shows a great
sensitivity to the radiative and microphysical properties of these clouds.
Our study presents a novel methodology that uses the thermal infrared
measurements of IIR to retrieve the ice crystal effective size and optical
thickness of cirrus. This methodology is based on an optimal estimation
scheme, which possesses the advantage of attributing precise uncertainties to
the retrieved parameters. Two IIR airborne validation campaigns have been
chosen as case studies for illustrating the results of our retrieval method.
It is observed that optical thicknesses could be accurately retrieved but
that large uncertainties may occur on the effective diameters. Strong
agreements have also been found between the products of our method when
separately applied to the measurements of IIR and of the airborne radiometer
CLIMAT-AV, which consolidates the results of previous validation studies of
IIR level-1 measurements. Comparisons with in situ observations and with
operational products of IIR are also discussed and appear to be coherent with
our results. However, we have found that the quality of our retrievals can be
strongly impacted by uncertainties related to the choice of a pristine
crystal model and by poor constraints on the properties of possible liquid
cloud layers underneath cirrus. Simultaneous retrievals of liquid clouds
radiative and microphysical properties and/or the use of different ice
crystal models should therefore be considered in order to improve the quality
of the results. |
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