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| Titel |
Explicit representation of subgrid variability in cloud microphysics yields weaker aerosol indirect effect in the ECHAM5-HAM2 climate model |
| VerfasserIn |
J. Tonttila, H. Järvinen, P. Räisänen |
| 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 ; 15, no. 2 ; Nr. 15, no. 2 (2015-01-19), S.703-714 |
| Datensatznummer |
250119334
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| Publikation (Nr.) |
 copernicus.org/acp-15-703-2015.pdf |
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| Zusammenfassung |
| The impacts of representing cloud microphysical processes in
a stochastic subcolumn framework are investigated, with emphasis on
estimating the aerosol indirect effect. It is shown that subgrid
treatment of cloud activation and autoconversion of cloud water to
rain reduce the impact of anthropogenic aerosols on cloud properties
and thus reduce the global mean aerosol indirect effect by
19%, from −1.59 to
−1.28 W m−2.
This difference is partly related to
differences in the model basic state; in particular, the liquid
water path (LWP) is smaller and the shortwave cloud
radiative forcing weaker when autoconversion is computed separately for each
subcolumn. However, when the model is retuned so
that the differences in the basic state LWP and radiation balance are
largely eliminated, the global-mean aerosol indirect effect is still
14% smaller (i.e. −1.37 W m−2) than for the
model version without subgrid treatment of cloud activation and
autoconversion.
The results show the importance
of considering subgrid variability in the treatment of
autoconversion. Representation of several processes in a self-consistent
subgrid framework is emphasized. This paper provides evidence
that omitting subgrid variability in cloud microphysics
contributes to the apparently chronic overestimation
of the aerosol indirect effect by climate models, as compared to
satellite-based estimates. |
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