Geosci. Model Dev. Discuss., 4, 1643-1684, 2011
www.geosci-model-dev-discuss.net/4/1643/2011/
doi:10.5194/gmdd-4-1643-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Geoscientific Model Development (GMD). Please refer to the corresponding final paper in GMD.
A subgrid parameterization scheme for precipitation
S. Turner, J.-L. Brenguier, and C. Lac
Groupe d'étude de l'atmosphère météorologique/CNRM Météo-France, URA1357, 42 Av Gaspard Coriolis, 31057 Toulouse Cedex 1, France

Abstract. With increasing computing power, the horizontal resolution of numerical weather prediction (NWP) models is improving and today reaches 1 to 5 km. Nevertheless, clouds and precipitation are still subgrid scale processes for most cloud types, such as cumulus and stratocumulus. Subgrid scale parameterizations for water vapor condensation have been in use for many years and are based on a prescribed PDF of relative humidity spatial variability within the grid, thus providing a diagnosis of the cloud fraction. A similar scheme is developed and tested here. It is based on a prescribed PDF of cloud water variability and a threshold value of liquid water content for droplet collection to derive a rain fraction within the model grid. Precipitation of rainwater raises additional concerns relative to the overlap of cloud and rain fractions, however. The scheme is developed following an analysis of data collected during field campaigns in stratocumulus (DYCOMS-II) and fair weather cumulus (RICO) and tested in a 1-D framework against large eddy simulations of these observed cases. The new parameterization is then implemented in a 3-D NWP model with a horizontal resolution of 2.5 km to simulate real cases of precipitating cloud systems over France.

Citation: Turner, S., Brenguier, J.-L., and Lac, C.: A subgrid parameterization scheme for precipitation, Geosci. Model Dev. Discuss., 4, 1643-1684, doi:10.5194/gmdd-4-1643-2011, 2011.
 
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