Requirements and Problems in Parallel Model Development at DWD

Nearly 30 years after introducing the first computer model for weather forecasting, the Deutscher Wetterdienst (DWD) is developing the 4th generation of its numerical weather prediction (NWP) system. It consists of a global grid point model (GME) based on a triangular grid and a non-hydrostatic Lokal Modell (LM). The operational demand for running this new system is immense and can only be met by parallel computers. From the experience gained in developing earlier NWP models, several new problems had to be taken into account during the design phase of the system. Most important were portability (including efficieny of the programs on several computer architectures) and ease of code maintainability. Also the organization and administration of the work done by developers from different teams and institutions is more complex than it used to be. This paper describes the models and gives some performance results. The modular approach used for the design of the LM is explained and the effects on the development are discussed