Four‐dimensional variational analyses of FASTEX situations using special observations

This paper focuses on Intensive Observation Period 17 of the Fronts and Atlantic Storm‐Track EXperiment (FASTEX): the FASTEX special soundings obtained during that period are added to the conventional dataset and assimilated with a 4‐dimensional variational (4D‐Var) scheme under development at Météo‐France. Results show a consistent use of the high density FASTEX ship soundings by the 4D‐Var formulation and an improvement brought by this new scheme over 3D‐Var when using only the vertical profiles synchronous with synoptic time. the application of the 4D‐Var analysis to dropsondes launched by a system‐relative flight designed by the Joint Centre for Mesoscale Meteorology also produces a fine‐scale description of sub‐structures of the mature system.