Impact of the MAP reanalysis on the numerical simulation of the MAP-IOP2a convective system

Numerical simulations of the convective system observed during the MAP IOP2a have been performed with the Meso-NH mesoscale model, using a threefold nesting technique with horizontal mesh-sizes of 32, 8 and 2 km. The reference experiment initialized from the operational ECMWF analysis of 17 September 1999 12 UTC succeeds reasonably well in initiating the convective line over the Alpine foothills and reproducing its propagation towards the East. The sensitivity of these results to the reanalysis products is investigated. In the ECMWF MAP reanalysis, the lower atmosphere above Northern Italy is found considerably drier than in the operational analysis. As a consequence, convection is almost entirely inhibited in the mesoscale simulations based upon the reanalysis. Different sensitivity experiments further highlight the strong dependence of the mesoscale results upon the initial moisture fields.