The Hirlam project [meteorology

Abstract

In 1985 the national meteorological institutes of Denmark, Finland, Iceland, The Netherlands, Norway, and Sweden joined forces to develop and maintain a numerical short range weather forecasting system. Later Ireland and Spain joined the project, and the Hirlam (high resolution limited area modeling) project is now in its third phase. Version 2 of the Hirlam system, built during the second phase of the project, is now used in routine weather forecasting at almost all participating institutes. Modern numerical weather forecasting systems have three basic components: an analysis unit, a forecast model, and a postprocessor. Analysis provides the initial conditions for the model, based on recent observations and other sources of information. The forecast model spatially and temporally discretizes and then integrates the classical equations-Newton's second law, mass conservation, and thermodynamics. In the postprocessing step, the relevant weather phenomena (for example, wind speed at 10 m height) are calculated from the model variables. The article outlines the analysis unit, forecast model, and postprocessor of the Hirlam system, as well as its implementation on massively parallel processing systems.