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| Titel |
Aging of mineral dust during transport from the Sahara into the Cape Verde area - results from airborne measurements during SAMUM |
| VerfasserIn |
B. Weinzierl, D. Sauer, M. Esselborn, A. Petzold, A. Veira, M. Rose, S. Mund, M. Wirth, A. Ansmann, M. Tesche, S. Groß, V. Freudenthaler |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250071073
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| Zusammenfassung |
| The Saharan Mineral Dust Experiment (SAMUM) was conducted to better understand the
properties of fresh and aged mineral dust. Within SAMUM, two field missions were
performed: SAMUM-1 (summer 2006, Morocco) focused on the chemical, microphysical,
optical and radiative properties of fresh dust aerosol in the vertical column over the Sahara,
while SAMUM-2 (winter 2008, Cape Verde) concentrated on the properties of aged dust and
the mixing of mineral dust with biomass burning aerosol. During both field experiments,
the DLR Falcon research aircraft was equipped with an extensive set of aerosol
instruments for size, volatility, and absorption measurements, impactor sampling
for chemical analyses and with a nadir-looking High Spectral Resolution Lidar
(HSRL).
In the Cape Verde area, we found a complex stratification with dust covering the altitude
range below 2 km and tropical biomass burning layers aloft. We show that the aerosol type of
individual aerosol layers can be classified based on depolarization and lidar ratios and, in
addition, on in situ measured Ångström exponents of absorption åap. The dust layers had a
geometrical depth of 1.3 ± 0.4 km and showed a median åap of 3.95. The median
effective diameter Deff was 2.5 μm and the dust layers over Cape Verde yielded clear
signals of aging: large particles were depleted due to gravitational settling and the
accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The
tropical biomass layers had a depth of 2.0 ± 1.1 km and were characterized by a
median åap of 1.34. They always contained a certain amount of large dust particles
and showed a median Deff of 1.1 μm and a fine mode Deff,fine of 0.33. The
dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23
and 0.09, respectively. The median contributions of the dust and biomass burning
layers to the AOD of the total atmospheric column below 10 km were 75 and 37%,
respectively.
We present the properties of aerosol layers in the Cape Verde region and compare the
properties of aged dust with those of fresh dust observed close the Sahara. Changes in the size
distribution during transport will be discussed and the impact of the changed size distribution
on the radiation budget will be evaluated. |
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