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| Titel |
Development of two-moment cloud microphysics for liquid and ice within the NASA Goddard Earth Observing System Model (GEOS-5) |
| VerfasserIn |
D. Barahona, A. Molod, J. Bacmeister, A. Nenes, A. Gettelman, H. Morrison, V. Phillips, A. Eichmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 7, no. 4 ; Nr. 7, no. 4 (2014-08-20), S.1733-1766 |
| Datensatznummer |
250115681
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| Publikation (Nr.) |
 copernicus.org/gmd-7-1733-2014.pdf |
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| Zusammenfassung |
| This work presents the development of a two-moment cloud microphysics scheme
within version 5 of the NASA Goddard Earth Observing System (GEOS-5). The
scheme includes the implementation of a comprehensive stratiform microphysics
module, a new cloud coverage scheme that allows ice supersaturation, and a
new microphysics module embedded within the moist convection parameterization
of GEOS-5. Comprehensive physically based descriptions of ice nucleation,
including homogeneous and heterogeneous freezing, and liquid droplet
activation are implemented to describe the formation of cloud particles in
stratiform clouds and convective cumulus. The effect of preexisting ice
crystals on the formation of cirrus clouds is also accounted for. A new
parameterization of the subgrid-scale vertical velocity distribution
accounting for turbulence and gravity wave motion is also implemented. The
new microphysics significantly improves the representation of liquid water
and ice in GEOS-5. Evaluation of the model against satellite retrievals and
in situ observations shows agreement of the simulated droplet and ice crystal
effective radius, the ice mass mixing ratio and number concentration, and the
relative humidity with respect to ice. When using the new microphysics, the
fraction of condensate that remains as liquid follows a sigmoidal dependency
with temperature, which is in agreement with observations and which
fundamentally differs from the linear increase assumed in most models. The
performance of the new microphysics in reproducing the observed total cloud
fraction, longwave and shortwave cloud forcing, and total precipitation is
similar to the operational version of GEOS-5 and in agreement with satellite
retrievals. The new microphysics tends to underestimate the coverage of
persistent low-level stratocumulus. Sensitivity studies showed that the
simulated cloud properties are robust to moderate variation in cloud microphysical
parameters. Significant sensitivity remains to variation in the dispersion of
the ice crystal size distribution and the critical size for ice
autoconversion. Despite these issues, the implementation of the new
microphysics leads to a considerably improved and more realistic
representation of cloud processes in GEOS-5, and allows the linkage of cloud
properties to aerosol emissions. |
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