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| Titel |
Radiative forcing by aerosols as derived from the AeroCom present-day and pre-industrial simulations |
| VerfasserIn |
M. Schulz, C. Textor, S. Kinne, Y. Balkanski, S. Bauer, T. Berntsen, T. Berglen, O. Boucher, F. Dentener, S. Guibert, I. S. A. Isaksen, T. Iversen, D. Koch, A. Kirkevåg, X. Liu, V. Montanaro, G. Myhre, J. E. Penner, G. Pitari, S. Reddy, Ø. Seland, P. Stier, T. Takemura |
| 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 ; 6, no. 12 ; Nr. 6, no. 12 (2006-11-16), S.5225-5246 |
| Datensatznummer |
250004181
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| Publikation (Nr.) |
 copernicus.org/acp-6-5225-2006.pdf |
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| Zusammenfassung |
| Nine different global models with detailed aerosol modules have
independently produced instantaneous direct radiative forcing due to
anthropogenic aerosols. The anthropogenic impact is derived from the
difference of two model simulations with prescribed aerosol
emissions, one for present-day and one for pre-industrial conditions. The
difference in the solar energy budget at the top of the atmosphere (ToA) yields a
new harmonized estimate for the aerosol direct radiative forcing (RF) under
all-sky conditions. On a global annual basis RF is −0.22 Wm−2, ranging
from +0.04 to −0.41 Wm−2, with a
standard deviation of ±0.16 Wm−2. Anthropogenic nitrate and dust are
not included in this estimate. No model shows a significant positive all-sky
RF. The corresponding clear-sky RF is −0.68 Wm−2. The cloud-sky RF was
derived based on all-sky and clear-sky RF and modelled cloud cover. It was
significantly different from zero and ranged between −0.16 and +0.34 Wm−2.
A sensitivity analysis shows that the total aerosol RF is
influenced by considerable diversity in simulated residence times, mass
extinction coefficients and most importantly forcing efficiencies (forcing
per unit optical depth). The clear-sky forcing efficiency
(forcing per unit optical depth) has diversity comparable to that for the all-sky/
clear-sky forcing ratio. While the diversity in clear-sky forcing efficiency is
impacted by factors such as aerosol absorption, size, and surface albedo,
we can show that the all-sky/clear-sky forcing ratio is important
because all-sky forcing estimates require
proper representation of cloud fields and the correct relative altitude
placement between absorbing aerosol and clouds. The analysis of the sulphate
RF shows that long sulphate residence times are compensated by
low mass extinction coefficients and vice versa. This is explained by more sulphate
particle humidity growth and thus higher extinction in those models where
short-lived sulphate is present at lower altitude and vice versa. Solar
atmospheric forcing within the atmospheric column is estimated at +0.82±0.17 Wm−2.
The local annual average maxima of atmospheric forcing exceed +5 Wm−2
confirming the regional character of aerosol impacts on climate. The annual
average surface forcing is −1.02±0.23 Wm−2. With the current
uncertainties in the modelling of the radiative forcing
due to the direct aerosol effect we show here that an estimate from one
model is not sufficient but a combination of several model estimates
is necessary to provide a mean and to explore the uncertainty. |
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