A PDF-based hybrid prognostic cloud scheme for general circulation models |
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Authors: | Masahiro Watanabe S Emori M Satoh H Miura |
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Institution: | (1) Center for Climate System Research, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568, Japan;(2) National Institute for Environmental Studies, Tsukuba, Japan;(3) Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan |
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Abstract: | A new cloud parameterization based on prognostic equations for the subgrid-scale fluctuations in temperature and total water
content is introduced for global climate models. The proposed scheme, called hybrid prognostic cloud (HPC) parameterization,
employs simple probability density functions (PDFs) to the horizontal subgrid-scale inhomogeneity, allowing them to vary in
shape in response to small-scale processes such as cumulus detrainment and turbulent mixing. Simple tests indicate that the
HPC scheme is highly favorable as compared to a diagnostic scheme in terms of the cloud fraction and cloud water content under
either uniform or non-uniform forcing. The relevance of the HPC scheme is investigated by implementing it in an atmospheric
component model of the climate model MIROC with a coarse resolution of T42. A comparison of the short-term integrations between
the T42 model and a global cloud resolving model (GCRM) reveals that the HPC scheme can reproduce, to a certain degree, the
subgrid-scale variance and skewness of temperature and total water content simulated in the GCRM. It is also found that the
HPC scheme significantly alters the climatological distributions in cloud cover, precipitation, and moisture, which are all
improved from the model using a conventional diagnostic cloud scheme. |
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