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| Titel |
Sensitivity of boreal-summer circulation and precipitation to atmospheric aerosols in selected regions – Part 1: Africa and India |
| VerfasserIn |
Y. C. Sud, E. Wilcox, W. K.-M. Lau, G. K. Walker, X.-H. Liu, A. Nenes, D. Lee, K.-M. Kim, Y. Zhou, P. S. Bhattacharjee |
| 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.3989-4007 |
| Datensatznummer |
250016687
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3989-2009.pdf |
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| Zusammenfassung |
| Version-4 of the Goddard Earth Observing System (GEOS-4) General Circulation
Model (GCM) was employed to assess the influence of potential changes in
aerosols on the regional circulation, ambient temperatures, and
precipitation in four selected regions: India and Africa (current paper), as
well as North and South America (companion paper). Ensemble-simulations were
carried out with the GCM to assess the aerosol direct and indirect effects,
hereafter ADE and AIE. Each simulation was started from the NCEP-analyzed
initial conditions for 1 May and was integrated through May-June-July-August
of each year: 1982–1987 to provide an ensemble set of six simulations. In
the first set, called experiment (#1), climatological aerosols were
prescribed. The next two experiments (#2 and #3) had two sets of
simulations each: one with 2X and other with 1/2X the climatological
aerosols over each of the four selected regions. In experiment #2, the
anomaly regions were advectively restricted (AR), i.e., the large-scale
prognostic fields outside the aerosol anomaly regions were prescribed while
in experiment #3, the anomaly regions were advectively Interactive (AI) as
is the case in a normal GCM integrations, but with the same aerosols
anomalies as in experiment #2. Intercomparisons of circulation, diabatic
heating, and precipitation difference fields showed large disparities among
the AR and AI simulations, which raised serious questions about the
proverbial AR assumption, commonly invoked in regional climate simulation
studies. Consequently AI simulation mode was chosen for the subsequent
studies. Two more experiments (#4 and #5) were performed in the AI
mode in which ADE and AIE were activated one at a time. The results showed
that ADE and AIE work in concert to make the joint influences larger than
sum of each acting alone. Moreover, the ADE and AIE influences were vastly
different for the Indian and Africa regions, which suggest an imperative
need to include them rationally in climate models. We also found that the
aerosol induced increase of tropical cirrus clouds would potentially offset
any cirrus thinning that may occur due to warming in response to CO2
increase. |
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