Using meteosat data to validate a prognostic cloud generation scheme

We have designed a cloud generation scheme for use in the LMD GCM. It predicts the mixing ratio of the cloud's condensed water as a new prognostic variable. At present it does not fully interact with the radiation schemes, but the aim is to predict the cloud optical properties. We have used the Meteosat/ISCCP data to evaluate this scheme. Such a comparison allows us to place some constraints on the coefficients which are used in the parameterizations, such as the precipitation thresholds for the cloud's liquid water content and the relative variability of water vapour within a grid box. There is generally a good agreement between observed and simulated results, although there appear some discrepancies in the cloud's apparent temperatures.