Implementation of a new assimilation scheme for soil and surface variablesin a global NWP model

Major changes have been introduced in the description of the soil-atmospher e-vegetation interactions in the global numerical weather prediction model ARPEGE and the embedded limited area model ALADIN used at Meteo-France. The Interaction Soil Biosphere Atmosphere (ISBA) parameterization is now used to describe exchanges between the atmosphere and the land surface. The anal ysis scheme for soil moisture has been changed accordingly and is now based on an optimal interpolation type using 2-m observations of temperature and relative humidity. Additionally, the description of land surface and veget ation characteristics has been improved by the use of new datasets. The ove rall impact of these modifications is a clear improvement in the forecast o f low-level fields and of the global hydrological cycle.