The ALADIN model was entirely built on the notion of compatibility with its « mother » system, IFS/ARPEGE.
The latter, a joint development between the European Centre for Medium-Range Weather Forecasts (ECMWF) and Météo-France , is only meant to consider global Numerical Weather Prediction applications ;
at the start of the ALADIN project, the decision was taken to complement the IFS/ARPEGE project with a limited area model (LAM) version, while keeping the differences between the two softwares as small as possible.
It was, therefore, necessary to copy the organization of the code from one system to the other by ensuring as much as possible integration, flexibility, modularity and generality. After about 10 years of development and evolution, the Aladin model software furthermore became the basis for the Arome and Alaro models.
The duality between ARPEGE (global with the possibility of variable resolution) and ALADIN (LAM), sharing the same grid-point observation operators, dynamics and physics, has allowed to tackle several NWP challenges at high resolution. For example, inside the two projects, advanced (variational) data-assimilation aspects have mostly been addressed in the global framework, while high-resolution aspects (non-hydrostatism) were explored in the LAM framework.
ALADIN and its declinations are presently operational in about 16 countries. Four 3D-Var data assimilation versions are deployed in as many French overseas regions, and another one that uses the initial conditions of the ECMWF global model is used over mainland France. The ALADIN model as such is geared to run with a 7 to 10 km resolution, which makes it an invaluable numerical weather prediction tool over geographical areas of the Globe where global models have a coarser resolution, as well as a computationally cheap forecast system over limited areas. ALADIN also can be used inside a downscaling system between global and very high resolution forecast models, as an intermediary coupling device.