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| Titel |
Modeling the influences of aerosols on pre-monsoon circulation and rainfall over Southeast Asia |
| VerfasserIn |
D. Lee, Y. C. Sud, L. Oreopoulos, K.-M. Kim, W. K. Lau, I.-S. Kang |
| 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 ; 14, no. 13 ; Nr. 14, no. 13 (2014-07-04), S.6853-6866 |
| Datensatznummer |
250118867
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| Publikation (Nr.) |
 copernicus.org/acp-14-6853-2014.pdf |
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| Zusammenfassung |
| We conduct several sets of simulations with a version of NASA's Goddard Earth
Observing System, version 5, (GEOS-5) Atmospheric Global Climate Model (AGCM)
equipped with a two-moment cloud microphysical scheme to understand the role
of biomass burning aerosol (BBA) emissions in Southeast Asia (SEA) in the
pre-monsoon period of February–May. Our experiments are designed so that
both direct and indirect aerosol effects can be evaluated. For
climatologically prescribed monthly sea surface temperatures, we conduct sets
of model integrations with and without biomass burning emissions in the area
of peak burning activity, and with direct aerosol radiative effects either
active or inactive. Taking appropriate differences between AGCM experiment
sets, we find that BBA affects liquid clouds in statistically significantly
ways, increasing cloud droplet number concentrations, decreasing droplet
effective radii (i.e., a classic aerosol indirect effect), and locally
suppressing precipitation due to a deceleration of the autoconversion
process, with the latter effect apparently also leading to cloud condensate
increases. Geographical re-arrangements of precipitation patterns, with
precipitation increases downwind of aerosol sources are also seen, most
likely because of advection of weakly precipitating cloud fields. Somewhat
unexpectedly, the change in cloud radiative effect (cloud forcing) at surface
is in the direction of lesser cooling because of decreases in cloud fraction.
Overall, however, because of direct radiative effect contributions, aerosols
exert a net negative forcing at both the top of the atmosphere and, perhaps
most importantly, the surface, where decreased evaporation triggers feedbacks
that further reduce precipitation. Invoking the approximation that direct and
indirect aerosol effects are additive, we estimate that the overall
precipitation reduction is about 40% due to the direct effects of
absorbing aerosols, which stabilize the atmosphere and reduce surface latent
heat fluxes via cooler land surface temperatures. Further refinements of our
two-moment cloud microphysics scheme are needed for a more complete
examination of the role of aerosol–convection interactions in the seasonal
development of the SEA monsoon. |
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