Evaluation of a cloud system life-cycle simulated by the Meso-NH model during FASTEX using METEOSAT radiances and TOVS-3I cloud retrievals

The evaluation of a simulation over the life-cycle of a cloud system during the Fronts and Atlantic Storm-Track EXperiment is made by comparing synthe tic and METEOSAT observed radiances. The usefulness of a 'model-to-satellit e' approach, combining an explicit cloud scheme implemented in a mesoscale model (the Meso-NH model) with a detailed radiative-transfer code, is shown . In clear sky, accuracy in the brightness-temperature simulations are, res pectively, about 4.5 K for the infrared channel and 2 K for the water-vapou r channel. In cloudy areas, comparison with the TOVS-3I cloud parameters sh ows that these errors become twice as large. The occurrence of key patterns in the simulated infrared images confirms the good quality of the model fo recast and the accuracy of the radiative code. On the other hand, the discr epancies identified by the approach show that the model overestimates the u pper-level cloud cover. It is suggested that this overestimation might resu lt either from a too large water detrainment or from an overestimated water residence time in the upper atmosphere. Finally, using an ice-phase parame trization in the cloud scheme significantly improves the simulated cloud co ver, although this more advanced scheme does not correct the overestimation of upper-level cloud cover.