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| Titel |
Impact of an improved shortwave radiation scheme in the MAECHAM5 General Circulation Model |
| VerfasserIn |
C. Cagnazzo, E. Manzini, M. A. Giorgetta, P. M. de F. Forster, J. J. Morcrette |
| 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 ; 7, no. 10 ; Nr. 7, no. 10 (2007-05-14), S.2503-2515 |
| Datensatznummer |
250004983
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| Publikation (Nr.) |
 copernicus.org/acp-7-2503-2007.pdf |
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| Zusammenfassung |
| In order to improve the representation of ozone absorption in the
stratosphere of the MAECHAM5 general circulation model, the spectral
resolution of the shortwave radiation parameterization used in the model has
been increased from 4 to 6 bands. Two 20-years simulations with the general
circulation model have been performed, one with the standard and the other
with the newly introduced parameterization respectively, to evaluate the
temperature and dynamical changes arising from the two different
representations of the shortwave radiative transfer. In the simulation with
the increased spectral resolution in the radiation parameterization, a
significant warming of almost the entire model domain is reported. At the
summer stratopause the temperature increase is about 6 K and alleviates the
cold bias present in the model when the standard radiation scheme is used.
These general circulation model results are consistent both with previous
validation of the radiation scheme and with the offline clear-sky comparison
performed in the current work with a discrete ordinate 4 stream scattering
line by line radiative transfer model. The offline validation shows a
substantial reduction of the daily averaged shortwave heating rate bias
(1–2 K/day cooling) that occurs for the standard radiation parameterization
in the upper stratosphere, present under a range of atmospheric conditions.
Therefore, the 6 band shortwave radiation parameterization is considered to
be better suited for the representation of the ozone absorption in the
stratosphere than the 4 band parameterization. Concerning the dynamical
response in the general circulation model, it is found that the reported
warming at the summer stratopause induces stronger zonal mean zonal winds in
the middle atmosphere. These stronger zonal mean zonal winds thereafter
appear to produce a dynamical feedback that results in a dynamical warming
(cooling) of the polar winter (summer) mesosphere, caused by an increased
downward (upward) circulation in the winter (summer) hemisphere. In addition,
the comparison of the two simulations performed with the general circulation
model shows that the increase in the spectral resolution of the shortwave
radiation and the associated changes in the cloud optical properties result
in a warming (0.5–1 K) and moistening (3%–12%) of the upper tropical
troposphere. By comparing these modeled differences with previous works, it
appears that the reported changes in the solar radiation scheme contribute to
improve the model mean temperature also in the troposphere. |
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