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| Titel |
Saharan and Asian dust: similarities and differences determined by CALIPSO, AERONET, and a coupled climate-aerosol microphysical model |
| VerfasserIn |
L. Su, O. B. Toon |
| 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. 7 ; Nr. 11, no. 7 (2011-04-05), S.3263-3280 |
| Datensatznummer |
250009591
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| Publikation (Nr.) |
 copernicus.org/acp-11-3263-2011.pdf |
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| Zusammenfassung |
| This study compares the properties of atmospheric dust from the Saharan
deserts and the Asian deserts using data from CALIPSO and AERONET during
2006 and 2007 along with simulations using a coupled climate-microphysical
sectional model. Saharan deserts are largely south of 30° N, while Asian ones
are primarily north of 30° N, hence they experience different meteorological
regimes. Saharan dust lifting occurs all year long, primarily due to
subtropical weather systems. However, Asian dust is lifted mostly in spring
when mid-latitude frontal systems lead to high winds. Rainfall is more
abundant over Asia during the dust lifting events, leading to greater local
dust removal than over the Sahara. However, most dust removal is due to
sedimentation. Despite the different meteorological regimes, the same dust
lifting schemes work in models for Asian and Saharan dust. The magnitudes of
dust lifted in Africa and Asia differ significantly over the year. In our
model the yearly horizontal dust flux just downwind of the African dust
source is about 1088 Tg (10° S–40° N, 10° W) and from the Asian dust source it is
about 355 Tg (25° N–55° N, 105° E) in 2007, which is comparable to previous
studies. We find the difference in dust flux is mainly due to the larger
area over which dust is lifted in Africa than Asia. However, Africa also has
stronger winds in some seasons. Once lifted, the Saharan dust layers
generally move toward the west and descend in altitude from about 7 km to the
surface over several days in the cases studied. Asian dust often has
multiple layers (two layers in the cases studied) during transport largely
to the east. One layer stays well above boundary layer during transport and
shows little descent, while the other, lower, layer descends with time. This
observation contrasts with studies suggesting the descent of Saharan dust is
due to sedimentation of the particles, and suggests instead it is dominated
by meteorology. We find the size distributions of Asian and African dust are
similar when the dust is lifted, but the mode size can differ and secondary
size modes can develop probably due to differences in vertical wind
velocities during transport. The single scattering albedo of African and
Asian dust does differ, due primarily to the imaginary parts of the
refractive indexes being different, which in turn is likely due to different
dust composition. This study is a step towards a global understanding of
dust and its properties. |
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