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| Titel |
Absorption of aerosols above clouds from POLDER/PARASOL measurements and estimation of their direct radiative effect |
| VerfasserIn |
F. Peers, F. Waquet, C. Cornet, P. Dubuisson, F. Ducos, P. Goloub, F. Szczap, D. Tanré, F. Thieuleux |
| 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 ; 15, no. 8 ; Nr. 15, no. 8 (2015-04-22), S.4179-4196 |
| Datensatznummer |
250119659
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| Publikation (Nr.) |
 copernicus.org/acp-15-4179-2015.pdf |
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| Zusammenfassung |
| This study presents an original method to evaluate key parameters for the
estimation of the direct radiative effect (DRE) of aerosol above clouds: the
absorption of the the cloud albedo. It is
based on multi-angle total and polarized radiances both provided by the
A-train satellite instrument POLDER – Polarization and Directionality of
Earth Reflectances. The sensitivities brought by each kind of measurements
are used in a complementary way. Polarization mostly translates scattering
processes and is thus used to estimate scattering aerosol optical
thickness and aerosol size. On the other hand, total radiances, together
with the scattering properties of aerosols, are used to evaluate the
absorption optical thickness of aerosols and cloud optical thickness. The
retrieval of aerosol and clouds properties (i.e., aerosol and cloud optical
thickness, aerosol single scattering albedo and Ångström exponent) is
restricted to homogeneous and optically thick clouds (cloud optical thickness
larger than 3). In addition, a procedure has been developed to process the
shortwave DRE of aerosols above clouds. Three case
studies have been selected: a case of absorbing biomass burning aerosols
above clouds over the southeast Atlantic Ocean, a Siberian biomass burning
event and a layer of Saharan dust above clouds off the northwest coast of Africa. Besides these case studies,
both algorithms have been applied to the southeast Atlantic Ocean and the results have been averaged during August 2006. The
mean DRE is found to be 33.5 W m−2 (warming).
Finally, the effect of the heterogeneity of clouds has been investigated and
reveals that it affects mostly the retrieval of the cloud optical thickness
and not greatly the aerosols properties. The homogenous cloud assumption used in
both the properties retrieval and the DRE processing leads to a slight
underestimation of the DRE. |
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