Validation and intercomparison of three mesoscale models on three FASTEX cloud systems: comparison with coarse‐resolution simulations

Taking advantage of the observations collected during the Fronts and Atlantic Storm‐Track EXperiment (FASTEX), three FASTEX midlatitude cloud systems are simulated with three state‐of‐the‐art, mesoscale, limited‐area models (the Met Office's Unified Model (UM), Met Éireann's High Resolution Limited Area Model (HIRLAM), and the French Laboratoire d'Aérologie research modèle de Méso‐échelle Non‐Hydrostatique (Méso‐NH)), at an 11 km horizontal resolution and with about 50 vertical levels. The dynamical, thermodynamic, cloud and precipitation fields obtained from these numerical integrations are then intercompared and validated against various observational sources, including radio‐ and dropsondes, satellite radiometer, and rain‐gauges. The similarities and the deficiencies of the three models are summarized in the paper. After this validation work, the mesoscale fields are degraded in resolution, so that they can be directly compared with the outputs of 300 km resolution simulations, run with Météo‐France's atmospheric general‐circulation model (AGCM) Action de Recherche Petite Echelle et Grande Echelle (ARPEGE). The deviations between the upscaled mesoscale models and the coarse AGCM turn out to be significant and highly dependent on the location relative to the storm, with, in particular, a large contrast between the trailing cold region and the warm sector with thick layer clouds, suggesting the existence of some deficiencies in the AGCM. Copyright © Royal Meteorological Society, 2003. Peter Clark's contribution is Crown copyright.