Technical Note : The Modular Earth Submodel System ( MESSy ) – a new approach towards Earth System Modeling

Generally, the typical approach towards Earth System Modeling has been to couple existing models of different domains (land, ocean, atmosphere,. . .) offline, using output files of one model to provide input for the other. However, for a detailed study of the interactions and feedbacks between chemical, physical, and biological processes, 5 it is necessary to perform the coupling online. One strategy is to link the existing domain-specific models with a universal coupler. In many cases, however, a much simpler approach is more feasible. To achieve the online coupling, we have developed the Modular Earth Submodel System (MESSy). Data are exchanged between a base model and several submodels within one comprehensive model system. MESSy in-10 cludes a generalized interface structure for the standardized control of the submodels and their interconnections. The internal complexity of the submodels is controllable in a transparent and user friendly way. This provides remarkable new possibilities to study feedback mechanisms (by two-way coupling), e.g., by applying MESSy to a general circulation model (GCM).