TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing

Simulating the Earth’s mantle convection at full convective vigor on planetary scales is a fundamental challenge in Geodynamics even for state of the art high- performance computing (HPC) systems. Realistic Earth mantle convection simulations can contribute a decisive link between uncertain input parameters, such as rheology, and testable preconditions, such as dynamic topography. The vertical deflections predicted by such models may then be tested against the geological record. Considering realistic Earth-like Rayleigh numbers (∼ 10⁸) a resolution of the thermal boundary layer on the order of ∼ 10 km is necessary considering the volume of the Earth’s mantle. Simulating Earth’s mantle convection at this level of accuracy requires solving sparse indefinite systems with more than a trillion degrees of freedom, computational feasible on exascale HPC systems. This can only be achieved by mantle convection codes providing high degrees of parallelism and scalability. Earlier approaches from applying a prototype framework using hierarchical hybrid grids (HHG) as solvers for such systems demonstrated the scalability of the underlying concept for future generations of exascale computing systems. In consideration of the TerraNeo project, here we report on the progress of utilizing the improved framework HyTeG (Hybrid Tetrahedral Grids) based on matrix-free multigrid solvers in combination with highly efficient parallelization and scalability. This will allow to solve systems with more than a trillion degrees of freedom on present and future generations of exascale computing systems. We also report on the advances in developing the scalable mantle convection code TerraNeo using the HyTeG framework to realise extreme-scale mantle convection simulations with a resolution on the order of ∼ 1 km.