Cloud and microphysical schemes in ARPEGE and AROME models

Physics of AROME and ARPEGE models used at Météo-France are closer and closer, but nevertheless their microphysics and cloud schemes exhibit some differences. Both consider a 1-moment microphysical scheme, but AROME uses one more hydrometeor category, the graupel, which is particularly important in convective events. In AROME, a hail diagnostic has been prefered to an additional prognostic variable, based on vertically integrated graupel content. The sedimentation scheme is common between both models, but with one more term required in ARPEGE considering the microphysical processes occuring during the fall of the longer time step. The PDF used in the subgrid cloud schemes are also different. In addition to other aspects linked with mesoscale data assimilation, model grid and temporal sampling, these differences help AROME to have better rain forecasts than ARPEGE, especially in convective situations. Some developments are performed in Meso-NH in order to prepare the implementation of more advanced microphysical schemes in AROME.

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