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| Titel |
A GCM study of the response of the atmospheric water cycle of West Africa and the Atlantic to Saharan dust radiative forcing |
| VerfasserIn |
K. M. Lau, K.-M. Kim, Y. C. Sud, G. K. 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.4023-4037 |
| Datensatznummer |
250016689
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| Publikation (Nr.) |
 copernicus.org/angeo-27-4023-2009.pdf |
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| Zusammenfassung |
| The responses of the atmospheric water cycle and climate of West Africa and
the Atlantic to radiative forcing of Saharan dust are studied using the NASA
finite volume general circulation model (fvGCM), coupled to a mixed layer
ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that
underlines the responses of the atmospheric water cycle to dust forcing as
follow. During the boreal summer, as a result of large-scale atmospheric
feedback triggered by absorbing dust aerosols, rainfall and cloudiness are
enhanced over the West Africa/Eastern Atlantic ITCZ, and suppressed over the
West Atlantic and Caribbean region. Shortwave radiation absorption by dust
warms the atmosphere and cools the surface, while longwave has the opposite
response. The elevated dust layer warms the air over West Africa and the
eastern Atlantic. As the warm air rises, it spawns a large-scale onshore
flow carrying the moist air from the eastern Atlantic and the Gulf of
Guinea. The onshore flow in turn enhances the deep convection over West
Africa land, and the eastern Atlantic. The condensation heating associated
with the ensuing deep convection drives and maintains an anomalous
large-scale east-west overturning circulation with rising motion over West
Africa/eastern Atlantic, and sinking motion over the Caribbean region. The
response also includes a strengthening of the West African monsoon,
manifested in a northward shift of the West Africa precipitation over land,
increased low-level westerly flow over West Africa at the southern edge of
the dust layer, and a near surface westerly jet underneath the dust layer
over the Sahara. The dust radiative forcing also leads to significant
changes in surface energy fluxes, resulting in cooling of the West African
land and the eastern Atlantic, and warming in the West Atlantic and
Caribbean. The EHP effect is most effective for moderate to highly absorbing
dusts, and becomes minimized for reflecting dust with single scattering
albedo at 0.95 or higher. |
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