Evaluation of trade cumulus and the DualM parametrization in the ECMWF model

TitleEvaluation of trade cumulus and the DualM parametrization in the ECMWF model
Publication TypeReport
Date Published12/2009
Series/CollectionECMWF-ARM Report Series
Document Number4
AuthorsAhlgrimm, M, Köhler, M
Place of publicationShinfield Park, Reading

CALIPSO observations are used to assess trade cumulus cloudiness in three versions of the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts. The observations are recast onto the model grid, and two simple threshold criteria for cloud top height and cloud fraction are used to identify grid points containing trade cumulus clouds. The cloud fraction and top height distributions of the sample populations are then compared. Results show that all versions of the model overestimate the frequency of occurrence of trade cumulus clouds, but underestimate their cloud fraction when present. These effects partially compensate. Cloud top heights are overestimated in model cycles using the modified Tiedtke parameterization for shallow convection, but are in very good agreement with observations when the Dual Mass Flux parameterization is introduced.

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