Four-dimensional variational analyses of FASTEX situations using special observations

This paper focuses on Intensive Observation Period 17 of the Fronts and Atl antic Storm-Track EXperiment (FASTEX): the FASTEX special soundings obtaine d during that period are added to the conventional dataset and assimilated with a 4-dimensional variational (4D-Var) scheme under development at Meteo -France. Results show a consistent use of the high density FASTEX skip soun dings by the 4D-Var formulation and an Improvement brought by this new sche me over 3D-Var when using only the vertical profiles synchronous with synop tic time. The application of the 4D-Var analysis to dropsondes launched by a system relative flight designed by the Joint Centre for Mesoscale Meteoro logy also produces a fine scale description of sub-structures of the mature system.