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| Titel |
Optical properties of Saharan dust aerosol and contribution from the coarse mode as measured during the Fennec 2011 aircraft campaign |
| VerfasserIn |
C. L. Ryder, E. J. Highwood, P. D. Rosenberg, J. Trembath, J. K. Brooke, M. Bart, A. Dean, J. Crosier, J. Dorsey, H. Brindley, J. Banks, J. H. Marsham, J. B. McQuaid, H. Sodemann, R. Washington |
| 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. 1 ; Nr. 13, no. 1 (2013-01-11), S.303-325 |
| Datensatznummer |
250017552
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| Publikation (Nr.) |
 copernicus.org/acp-13-303-2013.pdf |
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| Zusammenfassung |
New in-situ aircraft measurements of Saharan dust originating from Mali,
Mauritania and Algeria taken during the Fennec 2011 aircraft campaign over a
remote part of the Sahara Desert are presented. Size distributions extending
to 300 μm are shown, representing measurements extending further into
the coarse mode than previously published for airborne Saharan dust. A
significant coarse mode was present in the size distribution measurements
with effective diameter (deff) from 2.3 to 19.4 μm and coarse mode
volume median diameter (dvc) from 5.8 to 45.3 μm. The mean size
distribution had a larger relative proportion of coarse mode particles than
previous aircraft measurements. The largest particles (with
deff > 12 μm, or dvc > 25 μm) were only
encountered within 1 km of the ground. Number concentration, mass loading and
extinction coefficient showed inverse relationships to dust age since
uplift. Dust particle size showed a weak exponential relationship to dust
age. Two cases of freshly uplifted dust showed quite different
characteristics of size distribution and number concentration.
Single Scattering Albed (SSA) values at 550 nm calculated from the measured size distributions revealed
high absorption ranging from 0.70 to 0.97 depending on the refractive index.
SSA was found to be strongly related to deff. New instrumentation
revealed that direct measurements, behind Rosemount inlets, overestimate SSA
by up to 0.11 when deff is greater than 2 μm. This is caused by
aircraft inlet inefficiencies and sampling losses. Previous measurements of
SSA from aircraft measurements may also have been overestimates for this
reason. Radiative transfer calculations indicate that the range of SSAs
during Fennec 2011 can lead to underestimates in shortwave atmospheric
heating rates by 2.0 to 3.0 times if the coarse mode is neglected. This will
have an impact on Saharan atmospheric dynamics and circulation, which should
be taken into account by numerical weather prediction and climate models. |
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