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| Titel |
Sensitivity studies of dust ice nuclei effect on cirrus clouds with the Community Atmosphere Model CAM5 |
| VerfasserIn |
X. Liu, X. Shi, K. Zhang, E. J. Jensen, A. Gettelman, D. Barahona, A. Nenes, P. Lawson |
| 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 ; 12, no. 24 ; Nr. 12, no. 24 (2012-12-19), S.12061-12079 |
| Datensatznummer |
250011679
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| Publikation (Nr.) |
 copernicus.org/acp-12-12061-2012.pdf |
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| Zusammenfassung |
| In this study the effect of dust aerosol on upper tropospheric cirrus clouds
through heterogeneous ice nucleation is investigated in the Community
Atmospheric Model version 5 (CAM5) with two ice nucleation
parameterizations. Both parameterizations consider homogeneous and
heterogeneous nucleation and the competition between the two mechanisms in
cirrus clouds, but differ significantly in the number concentration of
heterogeneous ice nuclei (IN) from dust. Heterogeneous nucleation on dust
aerosol reduces the occurrence frequency of homogeneous nucleation and thus
the ice crystal number concentration in the Northern Hemisphere (NH) cirrus
clouds compared to simulations with pure homogeneous nucleation. Global and
annual mean shortwave and longwave cloud forcing are reduced by up to
2.0 ± 0.1 W m−2 (1σ uncertainty) and 2.4 ± 0.1 W m−2,
respectively due to the presence of dust IN, with the net cloud
forcing change of −0.40 ± 0.20 W m−2. Comparison of model
simulations with in situ aircraft data obtained in NH mid-latitudes suggests
that homogeneous ice nucleation may play an important role in the ice
nucleation at these regions with temperatures of 205–230 K. However,
simulations overestimate observed ice crystal number concentrations in the
tropical tropopause regions with temperatures of 190–205 K, and overestimate
the frequency of occurrence of high ice crystal number concentration
(> 200 L−1) and underestimate the frequency of low ice
crystal number concentration (< 30 L−1) at NH mid-latitudes.
These results highlight the importance of quantifying the number
concentrations and properties of heterogeneous IN (including dust aerosol)
in the upper troposphere from the global perspective. |
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