18th Conference on Weather and Forecasting, 14th Conference on Numerical Weather Prediction, and Ninth Conference on Mesoscale Processes

Monday, 30 July 2001: 1:15 PM
Recent improvements for surface and microphysical schemes in the MesoNH mesoscale model
Patrick Jabouille, CNRM, Toulouse, France; and J. P. Pinty, V. Masson, and F. Solmon
Poster PDF (983.0 kB)
The French community non-hydrostatic model MesoNH is a joint effort of Centre National de Recherches Meteorologiques (Meteo-France) and Laboratoire d'Aerologie (CNRS) to simulate the atmospheric motions, ranging from the large meso-alpha scale down to the micro-scale, with a comprehensive physical package.In this presentation, we will focus on two special parameterizations, the surface and microphysical schemes.

A bulk microphysical scheme with prediction of the concentrations and mixing ratios of cloud droplets and raindrops has been recently implemented in MesoNH. A description of this new scheme will be done and two cases of validation will be exposed. The first case is a simulation of Hawaiian rainband clouds. The 2D version of the model is used with a prescribed flow and results can be compared with other mesoscale models. This case allows focusing on key physical processes involved in the formation of warm rain. The second case is an orographically forced precipitating system located over the French mountain "les Cevennes". This simulation uses an original configuration. The grid nesting technique is applied with four embedded models, the coarse model (resolution of 50 km) that captures the large scale flow uses a classical Kessler scheme, while the fine model (resolution of 1 km) describing the cloud system over the mountain uses the new scheme.

Recent improvements have been also implemented in the surface scheme to provide more realistic lower boundary conditions for the atmospheric model. First, a town energy budget scheme (TEB) simulates turbulent fluxes for urban areas by taking into account contributions of walls, roads and roofs. Second, for natural land surfaces, it is possible to separately compute inside a grid mesh different surface fluxes associated with different kind of soil (forest, grassland, rocks ...).

An example of an urban heat island, which leads to the formation of an urban breeze will be presented.

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