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| Titel |
Investigating relationships between aerosol optical depth and cloud fraction using satellite, aerosol reanalysis and general circulation model data |
| VerfasserIn |
B. S. Grandey, P. Stier, T. M. Wagner |
| 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. 6 ; Nr. 13, no. 6 (2013-03-18), S.3177-3184 |
| Datensatznummer |
250018526
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| Publikation (Nr.) |
 copernicus.org/acp-13-3177-2013.pdf |
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| Zusammenfassung |
| Strong positive relationships between cloud fraction (fc) and
aerosol optical depth (τ) have been reported. Data retrieved from the
MODerate resolution Imaging Spectroradiometer (MODIS) instrument show
positive fc–τ relationships across most of the globe.
A global mean fc increase of approximately 0.2 between low and
high τ conditions is found for both ocean and land. However, these
relationships are not necessarily due to cloud–aerosol interactions. Using
state-of-the-art Monitoring Atmospheric Composition and Climate (MACC)
reanalysis-forecast τ data, which should be less affected by retrieval
artefacts, it is demonstrated that a large part of the observed
fc–τ signal may be due to cloud contamination of
satellite-retrieved τ. For longer MACC forecast time steps of 24 h,
which likely contain less cloud contamination, some negative
fc–τ relationships are found. The global mean
fc increase between low and high τ conditions is reduced
to 0.1, suggesting that cloud contamination may account for approximately one
half of the satellite-retrieved increase in fc. ECHAM5-HAM
general circulation model (GCM) simulations further demonstrate that positive
fc–τ relationships may arise due to covariation with
relative humidity. Widespread negative simulated fc–τ
relationships in the tropics are shown to arise due to scavenging of aerosol
by convective precipitation. Wet scavenging events are likely poorly sampled
in satellite-retrieved data, because the properties of aerosol below clouds
cannot be retrieved. Quantifying the role of wet scavenging, and assessing
GCM representations of this important process, remains a challenge for future
observational studies of aerosol–cloud–precipitation interactions. |
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