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| Titel |
Prognostic precipitation with three liquid water classes in the ECHAM5–HAM GCM |
| VerfasserIn |
V. Sant, R. Posselt, U. Lohmann |
| 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. 15 ; Nr. 15, no. 15 (2015-08-07), S.8717-8738 |
| Datensatznummer |
250119951
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| Publikation (Nr.) |
 copernicus.org/acp-15-8717-2015.pdf |
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| Zusammenfassung |
| A new parameterization with three prognostic liquid water
classes was implemented into the general circulation model (GCM) ECHAM5 with the
aerosol module HAM in order to improve the global representation of rain formation in marine
stratiform clouds. The additionally introduced drizzle class improves the
physical representation of the droplet spectrum and, more importantly,
improves the microphysical processes relevant for precipitation formation
compared to the standard parameterization. In order to avoid a mismatch of
the liquid and ice phase, a prognostic treatment of snow has been
introduced too. This has a significant effect on the amount and altitude of
ice clouds, which in turn affects not only the in- and outgoing radiation
but also the parameterized collection rates. With the introduction of a
prognostic precipitation scheme, a more realistic representation of both
liquid and ice phase large-scale precipitation is achieved compared to a
diagnostic treatment. An encouraging finding is that with the prognostic
treatment the increase of the liquid water path in response to anthropogenic
aerosols is reduced by about 25 %. Although the total net radiative
forcing is decreased from −1.3±0.3 to −1.6±0.3 W m−2 from
the control to the prognostic model version, the difference is within the
interannual variability. Altogether the results suggest that the treatment of
precipitation in global circulation models has not only a significant influence on the
phase of clouds and their conversion rates, but also hints towards uncertainties
related to a prognostic precipitation scheme. |
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