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| Titel |
Dust aerosol impact on North Africa climate: a GCM investigation of aerosol-cloud-radiation interactions using A-Train satellite data |
| VerfasserIn |
Y. Gu, K. N. Liou, J. H. Jiang, H. Su, X. Liu |
| 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 ; 12, no. 4 ; Nr. 12, no. 4 (2012-02-15), S.1667-1679 |
| Datensatznummer |
250010718
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| Publikation (Nr.) |
 copernicus.org/acp-12-1667-2012.pdf |
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| Zusammenfassung |
The climatic effects of dust aerosols in North Africa have been investigated
using the atmospheric general circulation model (AGCM) developed at the
University of California, Los Angeles (UCLA). The model includes an
efficient and physically based radiation parameterization scheme developed
specifically for application to clouds and aerosols. Parameterization of the
effective ice particle size in association with the aerosol first indirect
effect based on ice cloud and aerosol data retrieved from A-Train satellite
observations have been employed in climate model simulations. Offline
simulations reveal that the direct solar, IR, and net forcings by dust
aerosols at the top of the atmosphere (TOA) generally increase with
increasing aerosol optical depth. When the dust semi-direct effect is
included with the presence of ice clouds, positive IR radiative forcing is
enhanced since ice clouds trap substantial IR radiation, while the positive
solar forcing with dust aerosols alone has been changed to negative values
due to the strong reflection of solar radiation by clouds, indicating that
cloud forcing associated with aerosol semi-direct effect could exceed direct
aerosol forcing. With the aerosol first indirect effect, the net cloud
forcing is generally reduced in the case for an ice water path (IWP) larger
than 20 g m−2. The magnitude of the reduction increases with IWP.
AGCM simulations show that the reduced ice crystal mean effective size due
to the aerosol first indirect effect results in less OLR and net solar flux
at TOA over the cloudy area of the North Africa region because ice clouds
with smaller size trap more IR radiation and reflect more solar radiation.
The precipitation in the same area, however, increases due to the aerosol
indirect effect on ice clouds, corresponding to the enhanced convection as
indicated by reduced OLR. Adding the aerosol direct effect into the model
simulation reduces the precipitation in the normal rainfall band over North
Africa, where precipitation is shifted to the south and the northeast
produced by the absorption of sunlight and the subsequent heating of the air
column by dust particles. As a result, rainfall is drawn further inland to
the northeast.
This study represents the first attempt to quantify the climate impact of
the aerosol indirect effect using a GCM in connection with A-Train satellite
data. The parameterization for the aerosol first indirect effect developed
in this study can be readily employed for application to other GCMs. |
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