Mesoscale background error covariances: Recent results obtained with the limited-area model ALADIN over Morocco

This note presents recent results on the properties of background error covariances computed using the National Meteorological Center (now known as the National Centers for Environmental Prediction) method and applied to a mesoscale limited-area model. The error covariances are computed over a winter period for the Moroccan version of the ALADIN forecast system. The overall results compare well with previous outputs obtained with the same forecast model but on a typical midlatitude domain (viz., ALADIN-France). Thus. the climatological error statistics can be used with an equivalent efficiency in the frame of a 3DVAR analysis system over a wide range of low-latitude and midlatitude limited-area domains. Furthermore, the error statistics between the true forecast fields and the coupling fields for the same domain are compared. The coupling fields are provided by interpolation from the global ARPEGE model. The comparison gives insight into the range of scales over which ALADIN is building its own dynamics and errors. In particular, the study shows at what scale the limited-area model dynamics depart from the global model-forced solution.