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| Titel |
Sensitivity of boreal-summer circulation and precipitation to atmospheric aerosols in selected regions – Part 2: The Americas |
| VerfasserIn |
E. M. Wilcox, Y. C. Sud, G. Walker |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 10 ; Nr. 27, no. 10 (2009-10-23), S.4009-4021 |
| Datensatznummer |
250016688
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| Publikation (Nr.) |
 copernicus.org/angeo-27-4009-2009.pdf |
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| Zusammenfassung |
| Aerosol perturbations over selected land regions are imposed in Version-4 of
the Goddard Earth Observing System (GEOS-4) general circulation model (GCM)
to assess the influence of increasing aerosol concentrations on regional
circulation patterns and precipitation in four selected regions: India,
Africa, and North and South America. Part 1 of this paper addresses the
responses to aerosol perturbations in India and Africa. This paper presents
the same for aerosol perturbations over the Americas. GEOS-4 is forced with
prescribed aerosols based on climatological data, which interact with clouds
using a prognostic scheme for cloud microphysics including aerosol
nucleation of water and ice cloud hydrometeors. In clear-sky conditions the
aerosols interact with radiation. Thus the model includes comprehensive
physics describing the aerosol direct and indirect effects on climate
(hereafter ADE and AIE respectively). Each simulation is started from
analyzed initial conditions for 1 May and was integrated through
June-July-August of each of the six years: 1982–1987 to provide a 6-ensemble
set. Results are presented for the difference between simulations with
double the climatological aerosol concentration and one-half the
climatological aerosol concentration for three experiments: two where the
ADE and AIE are applied separately and one in which both the ADE and AIE are
applied. The ADE and AIE both yield reductions in net radiation at the top
of the atmosphere and surface while the direct absorption of shortwave
radiation contributes a net radiative heating in the atmosphere. A large net
heating of the atmosphere is also apparent over the subtropical North
Atlantic Ocean that is attributable to the large aerosol perturbation
imposed over Africa. This atmospheric warming and the depression of the
surface pressure over North America contribute to a northward shift of the
inter-Tropical Convergence Zone over northern South America, an increase in
precipitation over Central America and the Caribbean, and an enhancement of
convergence in the North American monsoon region. |
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