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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 5
Geosci. Model Dev., 6, 1641-1657, 2013
https://doi.org/10.5194/gmd-6-1641-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Geosci. Model Dev., 6, 1641-1657, 2013
https://doi.org/10.5194/gmd-6-1641-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Development and technical paper 08 Oct 2013

Development and technical paper | 08 Oct 2013

A refined statistical cloud closure using double-Gaussian probability density functions

A. K. Naumann1,2, A. Seifert3, and J. P. Mellado1 A. K. Naumann et al.
  • 1Max Planck Institute for Meteorology, 20146 Hamburg, Germany
  • 2International Max Planck Research School on Earth System Modelling (IMPRS-ESM), Max Planck Institute for Meteorology, 20146 Hamburg, Germany
  • 3Hans-Ertel Centre for Weather Research, Deutscher Wetterdienst, 20146 Hamburg, Germany

Abstract. We introduce a probability density function (PDF)-based scheme to parameterize cloud fraction, average liquid water and liquid water flux in large-scale models, that is developed from and tested against large-eddy simulations and observational data. Because the tails of the PDFs are crucial for an appropriate parameterization of cloud properties, we use a double-Gaussian distribution that is able to represent the observed, skewed PDFs properly. Introducing two closure equations, the resulting parameterization relies on the first three moments of the subgrid variability of temperature and moisture as input parameters. The parameterization is found to be superior to a single-Gaussian approach in diagnosing the cloud fraction and average liquid water profiles. A priori testing also suggests improved accuracy compared to existing double-Gaussian closures. Furthermore, we find that the error of the new parameterization is smallest for a horizontal resolution of about 5–20 km and also depends on the appearance of mesoscale structures that are accompanied by higher rain rates. In combination with simple autoconversion schemes that only depend on the liquid water, the error introduced by the new parameterization is orders of magnitude smaller than the difference between various autoconversion schemes. For the liquid water flux, we introduce a parameterization that is depending on the skewness of the subgrid variability of temperature and moisture and that reproduces the profiles of the liquid water flux well.

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