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| Titel |
Retrieval of the Eyjafjallajökull volcanic aerosol optical and microphysical properties from POLDER/PARASOL measurements |
| VerfasserIn |
F. Waquet, F. Peers, P. Goloub, F. Ducos, F. Thieuleux, Y. Derimian, J. Riedi, M. Chami, D. Tanré |
| 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 ; 14, no. 4 ; Nr. 14, no. 4 (2014-02-17), S.1755-1768 |
| Datensatznummer |
250118404
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| Publikation (Nr.) |
 copernicus.org/acp-14-1755-2014.pdf |
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| Zusammenfassung |
| Total and polarized radiances provided by the Polarization and
Directionality of Earth Reflectances (POLDER) satellite sensor are used to
retrieve the microphysical and optical properties of the volcanic plume
observed during the Eyjafjallajökull volcano eruption in 2010, over
cloud-free and cloudy ocean scenes. We selected two plume conditions, fresh
aerosols near the sources (three cases) and a downwind volcanic plume
observed over the North Sea 30 h after its injection into the atmosphere
(aged aerosols). In the near-source conditions, the aerosol properties
depend on the distance to the plume. Within the near-source plume, aerosols
are mainly non-spherical and in the coarse mode with an effective radius
equal to 1.75 (±0.25) μm and an Ångström exponent (AE)
close to 0.0. Far from the plume, in addition to the coarse mode, there are
particles retrieved in the accumulation mode, suggesting a mixture of
sulfate aerosols and volcanic dust, resulting in an AE around 0.8. The
properties of the aerosols also depend on whether the plume is fresh or
aged. For the downwind (aged) plume, if non-spherical coarse particles as
well as some fine mode particles are retrieved, the AE is higher,
around ~0.4. In addition, rather low values for the real part
of the refractive index (RR) were retrieved for the fresh plume (1.38 < RR < 1.48). Single scattering albedo (SSA) values ranging
between 0.92 and 0.98 were retrieved over some parts of the near-source plume;
despite the low accuracy of our retrievals, the derived SSA values suggest
that the ash particles are rather absorbing. To consider the particle shape,
a combination of spheroid models was used. Although the employed model
enabled accurate modeling of the POLDER signal in the case of non-spherical ash,
our approach failed to model the signal over the optically thickest parts of
the near-source plume. The most probable reason for this is the presence
of ice crystals within the plume. For the aerosol above clouds (AAC) scenes,
polarized measurements allowed the retrieval of the optical thickness (OT)
and the AE of optically thin volcanic ash. We found that all the cloud
parameters retrieved by passive sensors were biased due to the presence of
the elevated volcanic plumes. Finally, thermal infrared measurements were
used to identify the type of multilayer scene (cirrus clouds or
volcanic dust above liquid clouds) and the retrieval method also provided
the OT of thin cirrus layers above the clouds near Iceland. |
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