11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Friday, 7 June 2002
Fine Scale Simulation of Precipitation of MAP IOP2A with Sensitivity to Hail and Comparision with Radar Data.
Jean-Pierre Pinty, CNRS, Toulouse, France; and E. Richard and P. Tabary

Several 12 hour fine scale simulations of the main precipitating episode of the MAP (Mesoscale Alpine Programme) IOP2A, 17 Sept. 1999, have been performed at a resolution of 2 km using the two-way, triple nested non-hydrostatic mesoscale model MesoNH. A first series of numerical experiments suggests a strong sensitivity of the simulation to the initial analyse and to the lateral boundary conditions. We show that the 4DVAR analyse from ECMWF is fully able to initiate a first line of convection over the nord-west foothills of the Pô valley in Northern Italy after integrating MesoNH for 6 hours. As the system further develops and produces a copious amount of precipitation during its move to the east during the next 6 hours, we can explore the sensitivity of the precipitation to the bulk microphysical scheme of MesoNH by using 3 or 4 ice species, so considering or not hail as a full ice category. The results show that a separate treatment of hail-like hydrometeores leads to a more active and organized convective system with an increase of the precipitation. The numerical results are directly evaluated against a composite of reflectivity obtained from three aligned Doppler radars including S-Pol (deployed by NCAR). It is shown that the explicit treatment of hail, suggested by polarimetric informations extracted from S-Pol, provides also the best location of the rainfall in the 2 km scale simulation.

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