Coupled simulations in the Energy Exascale Earth System Model (E3SM) integrate complex models of the atmosphere, ocean, rivers, land surface, and sea ice into a single system, increasing the overall computational complexity and requiring robust numerical choices. The Model Coupling Toolkit (MCT) serves as the hub interface in the current E3SM models for component coupling but can be limited by its inability to compute linear maps online, necessitating pre-processing steps and reducing runtime flexibility.

To improve computational efficiency and scientific productivity, efforts have been made to transition from MCT to a topology-aware library, the Mesh Oriented datABase (MOAB). MOAB provides a comprehensive description of the topology for each submodel in E3SM and enables the serialization of coupled scalar and flux solution fields for nonlinear coupling. This approach supports arbitrary grids and adaptive decompositions, ensuring seamless operations like mesh intersections, conservative projection operator computation, and remapping weight application for transferring coupled field data between models. Integrating the MOAB mesh database within E3SM, with interfaces to TempestRemap, allows for the generation of remapping weights during simulations, eliminating the need for offline pre-processing.

We present detailed algorithmic and performance results of the new MOAB coupler and compare it with the existing E3SM-MCT coupler. Potential enhancements to the coupler, including high-order projection methods for property preservation and new distributed coupling interfaces, which move away from the traditional hub-and-spoke model, are also discussed. This transition aims to optimize computational efficiency and scientific output by leveraging MOAB’s advanced capabilities in mesh topology and data management.

References

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