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| Titel |
Sensitivity of LES simulations of the stratocumulus-topped boundary layer to turbulent mixing and radiative cooling |
| VerfasserIn |
Marcin J. Kurowski, Wojciech W. Grabowski, Szymon P. Malinowski |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035353
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| Zusammenfassung |
| The influence of various physical processes on the evolution of the stratocumulus-topped
boundary layer (STBL) is investigated in large-eddy simulations using the anelastic model
EULAG. Experiments are based on a setup presented in Stevens et al. (Mon. Wea. Rev. 2005)
and motivated by observations during the DYCOMS-II field campaign. The simulations
expand the analysis presented in Kurowski et al. (Quart. J. Roy. Meteor. Soc. 2009) by
investigating the impact of imposed changes in: (i) the prescribed radiative cooling at the top
of the cloud; (ii) the subgrid-scale mixing; and (iii) the representation of evaporation of cloud
water during turbulent mixing of cloudy air with warm and dry air entrained into STBL from
above the inversion. The changes in radiative cooling are included through a simple
multiplication of the model-calculated radiative cooling by a factor between 0.5 and 2. The
changes in the subgrid-scale mixing include modifications of the ratio between the
mixing coeficients for momentum and for scalars, that is, the turbulent Prandtl
number. The delay of a phase change associated with turbulent entrainment and
mixing is included following the approach of Grabowski (J. Atmos. Sci. 2007). In this
approach, the evaporation of cloud water due to parameterized mixing is postponed until
the subgrid-scale mixing reaches spatial scales close the Kolmogorov microscale.
According to the results, the largest contribution to the domain statistics comes
from the changes in the subgrid-scale mixing. The influence of radiative cooling is
significant only if the change in the forcing near stratocumulus top is strong enough
to disturb stability of the system, otherwise it is rather weak. The delay of phase
changes during the parameterized mixing seems to be of a less importance than other
processes. |
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