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| Titel |
Observations of Saharan dust microphysical and optical properties from the Eastern Atlantic during NAMMA airborne field campaign |
| VerfasserIn |
G. Chen, L. D. Ziemba, D. A. Chu, K. L. Thornhill, G. L. Schuster, E. L. Winstead, G. S. Diskin, R. A. Ferrare, S. P. Burton, S. Ismail, S. A. Kooi, A. H. Omar, D. L. Slusher, M. M. Kleb, J. S. Reid, C. H. Twohy, H. Zhang, B. E. Anderson |
| 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 ; 11, no. 2 ; Nr. 11, no. 2 (2011-01-26), S.723-740 |
| Datensatznummer |
250009195
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| Publikation (Nr.) |
 copernicus.org/acp-11-723-2011.pdf |
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| Zusammenfassung |
| As part of the international project entitled "African Monsoon
Multidisciplinary Analysis (AMMA)", NAMMA (NASA AMMA) aimed to gain a
better understanding of the relationship between the African Easterly Waves
(AEWs), the Sahara Air Layer (SAL), and tropical cyclogenesis. The NAMMA
airborne field campaign was based out of the Cape Verde Islands during the
peak of the hurricane season, i.e., August and September 2006. Multiple
Sahara dust layers were sampled during 62 encounters in the eastern portion
of the hurricane main development region, covering both the eastern North
Atlantic Ocean and the western Saharan desert (i.e., 5–22° N and 10–35° W). The centers of these layers were located at altitudes between 1.5
and 3.3 km and the layer thickness ranged from 0.5 to 3 km. Detailed dust
microphysical and optical properties were characterized using a suite of in-situ instruments aboard the NASA DC-8 that included a particle counter, an
Ultra-High Sensitivity Aerosol Spectrometer, an Aerodynamic Particle Sizer,
a nephelometer, and a Particle Soot Absorption Photometer. The NAAMA
sampling inlet has a size cut (i.e., 50% transmission efficiency size) of
approximately 4 μm in diameter for dust particles, which limits the
representativeness of the NAMMA observational findings. The NAMMA dust
observations showed relatively low particle number densities, ranging from
268 to 461 cm−3, but highly elevated volume density with an average at
45 μm3 cm−3. NAMMA dust particle size distributions can be
well represented by tri-modal lognormal regressions. The estimated volume
median diameter (VMD) is averaged at 2.1 μm with a small range of
variation regardless of the vertical and geographical sampling locations.
The Ångström Exponent assessments exhibited strong wavelength
dependence for absorption but a weak one for scattering. The single
scattering albedo was estimated at 0.97 ± 0.02. The imaginary part of
the refractive index for Sahara dust was estimated at 0.0022, with a range
from 0.0015 to 0.0044. Closure analysis showed that observed scattering
coefficients are highly correlated with those calculated from spherical
Mie-Theory and observed dust particle size distributions. These values are
generally consistent with literature values reported from studies with
similar particle sampling size range. |
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