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| Titel |
What does reflection from cloud sides tell us about vertical distribution of cloud droplet sizes? |
| VerfasserIn |
A. Marshak, J. V. Martins, V. Zubko, Y. J. Kaufman |
| 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. 12 ; Nr. 6, no. 12 (2006-11-20), S.5295-5305 |
| Datensatznummer |
250004185
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| Publikation (Nr.) |
 copernicus.org/acp-6-5295-2006.pdf |
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| Zusammenfassung |
Cloud development, the onset of precipitation and the effect of aerosol on
clouds depend on the structure of the cloud profiles of droplet size and
phase. Aircraft measurements of cloud profiles are limited in their temporal
and spatial extent. Satellites were used to observe cloud tops not cloud
profiles with vertical profiles of precipitation-sized droplets anticipated
from CloudSat. The recently proposed CLAIM-3D satellite mission (cloud
aerosol interaction mission in 3-D) suggests to measure profiles of cloud
microphysical properties by retrieving them from the solar and infrared
radiation reflected or emitted from cloud sides.
Inversion of measurements from the cloud sides requires rigorous
understanding of the 3-dimentional (3-D) properties of clouds. Here we
discuss the reflected sunlight from the cloud sides and top at two
wavelengths: one nonabsorbing to solar radiation (0.67 μm) and one with
liquid water efficient absorption of solar radiation (2.1 μm). In
contrast to the plane-parallel approximation, a conventional approach to all
current operational retrievals, 3-D radiative transfer is used for
interpreting the observed reflectances. General properties of the radiation
reflected from the sides of an isolated cloud are discussed. As a proof of
concept, the paper shows a few examples of radiation reflected from cloud
fields generated by a simple stochastic cloud model with the prescribed
vertically resolved microphysics. To retrieve the information about droplet
sizes, we propose to use the probability density function of the droplet
size distribution and its first two moments instead of the assumption about
fixed values of the droplet effective radius. The retrieval algorithm is
based on the Bayesian theorem that combines prior information about cloud
structure and microphysics with radiative transfer calculations. |
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