OASIS and PALM, the CERFACS couplers

Coupling numerical models, i.e. implementing synchronized exchanges of information between models, is a central issue in many research fields such as climate modelling, data assimilation, or computational fluid dynamics. Since about 15 years, CERFACS specializes in developing coupling software tools, also called “couplers”. In 1991, CERFACS was commissioned to develop a software interface to couple existing numerical General Circulation Models of the ocean (OGCMs) and of the atmosphere (AGCMs). Two years later, a first version of the OASIS coupler was distributed to the community. Today, both the widely used mono process OASIS3 coupler [1] and the new fully parallel OASIS4 coupler [2] are available. Concurrently, the development of the PALM coupler, originally designed for oceanographic data assimilation and therefore addressing parallel dynamic coupling, started in 1997. Two implementations of PALM are currently available, PALM Research and PALM MP [3] respectively based on Message Passing Interface MPI1 [4] and MPI2 [5]. This document gives an overview of the OASIS and PALM couplers, describing their analogies and differences, and concludes with a discussion on the possible interactions in their future development.