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| Titel |
Improving subtropical boundary layer cloudiness in the 2011 NCEP GFS |
| VerfasserIn |
J. K. Fletcher, C. S. Bretherton, H. Xiao, R. Sun, J. Han |
| 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. 5 ; Nr. 7, no. 5 (2014-09-23), S.2107-2120 |
| Datensatznummer |
250115724
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| Publikation (Nr.) |
 copernicus.org/gmd-7-2107-2014.pdf |
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| Zusammenfassung |
The current operational version of National Centers for Environmental
Prediction (NCEP) Global Forecasting System (GFS) shows significant low cloud
bias. These biases also appear in the Coupled Forecast System (CFS), which is
developed from the GFS. These low cloud biases degrade seasonal and longer
climate forecasts, particularly of short-wave cloud radiative forcing, and
affect predicted sea surface temperature. Reducing this bias in the GFS will
aid the development of future CFS versions and contributes to NCEP's goal of
unified weather and climate modelling.
Changes are made to the shallow convection and planetary boundary layer
parameterisations to make them more consistent with current knowledge of these
processes and to reduce the low cloud bias. These changes are tested in a
single-column version of GFS and in global simulations with GFS coupled to a
dynamical ocean model. In the single-column model, we focus on changing
parameters that set the following: the strength of shallow cumulus lateral
entrainment, the conversion of updraught liquid water to precipitation and
grid-scale condensate, shallow cumulus cloud top, and the effect of shallow
convection in stratocumulus environments. Results show that these changes
improve the single-column simulations when compared to large eddy
simulations, in particular through decreasing the precipitation efficiency of
boundary layer clouds. These changes, combined with a few other model
improvements, also reduce boundary layer cloud and albedo biases in global
coupled simulations. |
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