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| Titel |
Impact of the representation of marine stratocumulus clouds on the anthropogenic aerosol effect |
| VerfasserIn |
D. Neubauer, U. Lohmann, C. Hoose, M. G. Frontoso |
| 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. 21 ; Nr. 14, no. 21 (2014-11-14), S.11997-12022 |
| Datensatznummer |
250119161
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| Publikation (Nr.) |
 copernicus.org/acp-14-11997-2014.pdf |
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| Zusammenfassung |
Stratocumulus clouds are important for climate as they reflect large amounts
of solar radiation back into space. However they are difficult to simulate in
global climate models because they form under a sharp inversion and are
thin. A comparison of model simulations with the ECHAM6-HAM2 global aerosol
climate model to observations, reanalysis and literature data revealed too
strong turbulent mixing at the top of stratocumulus clouds and a lack of
vertical resolution. Further reasons for cloud biases in stratocumulus
regions are the too "active" shallow convection scheme, the cloud cover
scheme and possibly too low subsidence rates.
To address some of these issues and improve the representation of
stratocumulus clouds, we made three distinct changes to ECHAM6-HAM2. With a
"sharp" stability function in the turbulent mixing scheme we have observed,
similar to previous studies, increases in stratocumulus cloud cover and
liquid water path. With an increased vertical resolution in the lower
troposphere in ECHAM6-HAM2 the stratocumulus clouds form higher up in the
atmosphere and their vertical extent agrees better with reanalysis data. The
recently implemented in-cloud aerosol processing in stratiform clouds is
used to improve the aerosol representation in the model.
Including the improvements also affects the anthropogenic aerosol effect.
In-cloud aerosol processing in ECHAM6-HAM2 leads to a decrease in the anthropogenic aerosol effect in the global annual mean from −1.19 Wm−2 in
the reference simulation to −1.08 Wm−2, while using a "sharp" stability
function leads to an increase to −1.34 Wm−2. The results from the
simulations with increased vertical resolution are diverse but increase the
anthropogenic aerosol effect to −2.08 Wm−2 at 47 levels and
−2.30 Wm−2 at 95 levels. |
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