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| Titel |
A global survey of aerosol-liquid water cloud overlap based on four years of CALIPSO-CALIOP data |
| VerfasserIn |
A. Devasthale, M. A. Thomas |
| 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. 3 ; Nr. 11, no. 3 (2011-02-10), S.1143-1154 |
| Datensatznummer |
250009297
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| Publikation (Nr.) |
 copernicus.org/acp-11-1143-2011.pdf |
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| Zusammenfassung |
| Simulating the radiative impacts of aerosols located above liquid water
clouds presents a significant challenge. In particular, absorbing aerosols,
such as smoke, may have significant impact in such situations and even
change the sign of net radiative forcing. It is not possible to reliably
obtain information on such overlap events from existing passive satellite
sensors. However, the CALIOP instrument onboard NASA's CALIPSO satellite
allows us to examine these events with unprecedented accuracy. Using four
years of collocated CALIPSO 5 km Aerosol and Cloud Layer Version 3 Products
(June 2006–May 2010), we quantify, for the first time, the characteristics
of overlapping aerosol and water cloud layers globally. We investigate
seasonal variability in these characteristics over six latitude bands to
understand the hemispheric differences when all aerosol types are included
in the analysis (the AAO case). We also investigate frequency of smoke
aerosol-cloud overlap (the SAO case). Globally, the frequency is highest
during the JJA months in the AAO case, while for the SAO case, it is highest
in the SON months. The seasonal mean overlap frequency can regionally exceed
20% in the AAO case and 10% in the SAO case. In about 5–10% cases
the vertical distance between aerosol and cloud layers is less than 100 m,
while about in 45–60% cases it less than a kilometer in the annual means
for different latitudinal bands. In about 70–80% cases, aerosol layers
are less than a kilometer thick, while in about 18–22% cases they are 1–2 km thick. The frequency of aerosol layers 2–3 km thick is about 4–5% in
the tropical belts during overlap events. Over the regions where high
aerosol loadings are present, the overlap frequency can be up to 50%
higher when quality criteria on aerosol/cloud feature detection are relaxed.
Over the polar regions, more than 50% of the overlapping aerosol layers
have optical thickness less than 0.02, but the contribution from the
relatively optically thicker aerosol layers increases towards the equatorial
regions in both hemispheres. The results suggest that the frequency of
occurrence of overlap events is far from being negligible globally. |
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