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| Titel |
Aerosol-induced changes of convective cloud anvils produce strong climate warming |
| VerfasserIn |
I. Koren, L. A. Remer, O. Altaratz, J. V. Martins, A. Davidi |
| 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 ; 10, no. 10 ; Nr. 10, no. 10 (2010-05-31), S.5001-5010 |
| Datensatznummer |
250008491
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| Publikation (Nr.) |
 copernicus.org/acp-10-5001-2010.pdf |
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| Zusammenfassung |
The effect of aerosol on clouds poses one of the largest uncertainties in
estimating the anthropogenic contribution to climate change. Small
human-induced perturbations to cloud characteristics via aerosol pathways
can create a change in the top-of-atmosphere radiative forcing of hundreds
of Wm−2. Here we focus on links between aerosol and deep convective
clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting
that the aerosol environment in each region is entirely different. The tops
of these vertically developed clouds consisting of mostly ice can reach high
levels of the atmosphere, overshooting the lower stratosphere and reaching
altitudes greater than 16 km. We show a link between aerosol, clouds and the
free atmosphere wind profile that can change the magnitude and sign of the
overall climate radiative forcing.
We find that increased aerosol loading is associated with taller cloud
towers and anvils. The taller clouds reach levels of enhanced wind speeds
that act to spread and thin the anvil clouds, increasing areal coverage and
decreasing cloud optical depth. The radiative effect of this transition is
to create a positive radiative forcing (warming) at top-of-atmosphere.
Furthermore we introduce the cloud optical depth (τ), cloud height (Z)
forcing space and show that underestimation of radiative forcing is likely
to occur in cases of non homogenous clouds. Specifically, the mean radiative
forcing of towers and anvils in the same scene can be several times greater
than simply calculating the forcing from the mean cloud optical depth in the
scene.
Limitations of the method are discussed, alternative sources of aerosol
loading are tested and meteorological variance is restricted, but the trend
of taller clouds, increased and thinner anvils associated with increased
aerosol loading remains robust through all the different tests and
perturbations. |
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