A monitoring of the European Centre for Medium-Range Weather Forecasts (ECMWF) model with the Meteosat infrared window channel during December 2000 is presented. The Meteosat images are simulated every 3 h during the 31 days of the month from the model fields, at a resolution of 35 km. The study of both the spatial and the temporal variabilities of the model cloudiness is based on forecasts, from 3 to 48 h, as well as on analyses. Despite a reduced cloud forcing in the model, the variations of

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... he extratropical cyclones are shown to be well represented in the short-range (up to 1 day) forecasts. The intertropical convergence zone (ITCZ) is well located but the representation of its temporal variations significantly differs from the observations, in particular over land. The variability of the Meteosat brightness temperature time series usually differs by more than 10% from one model grid point to another, whereas the structures described by the model have scales of about three to four grid points at least. This work prepares the routine monitoring of the ECMWF analysis and forecast system with the raw images from Meteosat, soon to be replaced by the Meteosat Second Generation imager/sounder, and is an important step toward the assimilation of cloud-affected satellite radiances.