Combined use of sensitivity information and observations to improve meteorological forecasts: A feasibility study applied to the 'Christmas storm' case

An analysis correction method is presented that uses directly the sensitivi ty information coming from gradient fields at initial time to perform an al ternative forecast. The method consists in imposing, at initial time, a 'se nsitive' structure to the perturbation which is first computed by adjoint t ools. The tuning of the perturbation amplitude is obtained by reducing the distance to the observations at the locations where the sensitive structure is of significant amplitude. The method is tested on a severe meteorological event which was operational ly badly forecast even at very short ranges. Several sets of homogeneous ob servations are considered and the method proves its efficiency for part of them.