Medium-Range Forecasting at the ECMWF

This chapter describes medium-range forecasting at the European Centre for Medium Range Weather Forecasts (ECMWF). The division of weather forecasts into short-, medium-, and long-range is both logical and practical. Models used for medium-range forecasting are normally based on a set of equations known as the primitive equations. The governing dynamic, thermodynamic, and conservation equations are mapped to a spherical geometry, and the reduced set of primitive equations is obtained by assuming the height scale of the motion to be small compared with its horizontal-length scale, an acceptable approximation for horizontal scales upward of tens of kilometers. The associated parameterization scheme described the processes thought to be of importance in the medium range. These include a full hydrological cycle, a comparatively detailed representation of turbulence fluxes, and an interaction between radiation and model-generated clouds. Changes are computed in a number of land-surface characteristics used for the calculation of surface heat, moisture, and momentum fluxes. The tropical and southern hemisphere forecasts are also elaborated. © 1985, Elsevier Inc. All rights reserved