Comparison between the land surface response of the European Centre model and the FIFE-1987 data.

An averaged time series for the surface data for the 15 × 15 km FIFE site was prepared for the summer of 1987. Comparisons with 48-Hour forecasts from the ECMWF model for extended periods in July, August and October 1987 identified model errors in the incoming short-wave radiation in clear skies, the ground heat flux, the formulation of surface evaporation, the soil-moisture model, and entrainment at boundary-layer top. The model clear-sky short-wave flux is too high at the surface by 5-10%. The ground heat flux is too large by a factor of 2 to 3 because of the large thermal capacity of the first soil layer (which is 7 cm thick), and a time truncation error. The surface evaporation was near zero in October 1987, rather than of order 70 W m-2 at noon. The surface evaporation falls too rapidly after rainfall, with a time-scale of a few days rather than the 7-10 days (or more) of the observation. On time-scales of more than a few days the specified climate layer soil moisture, rather than the storage of precipitation, has a large control on the evapotranspiration. The order 2g Kg-1 in forecasts from an experimental analysis with nearly realistic surface fluxes; this because there is insufficient downward mixing of dry air.

Related Topics

• FIFE,
• Land-surface,
• Parameterization,
• Reanalysis&FX