CESM at the KM-Scale

The current hydrostatic NCAR CAM-SE in CESM is based on the High-Order Methods Modeling Environment (HOMME; Dennis et al. 2005; Taylor and Fournier 2010) which was jointly developed by the Department of Energy (DoE) and NCAR. With the creation of the Energy Exascale Earth System Model (E3SM, Golaz et al., 2019, 2022), DoE continued the development of HOMME with a nonhydrostatic extension of the hydrostatic SE formulation (Taylor et al. 2020). The new nonhydrostatic SE dynamical core was programmed both in Fortran and C++ with the use of the Kokkos library for GPU support (Caldwell et al. 2021; Taylor et al., 2023; Donahue et al., 2024). The two code bases are bit-for-bit identical without optimizations, and will both be utilized in this project. The Fortran version will serve as a workhorse for the scientific exemplars at cloud-permitting scales with grid spacings of about 3 km. The C++/Kokkos version is robust, but more experimental for NCAR. It will lay the foundation for future modern CESM software designs with GPU acceleration.

StormSPEED builds on the extensive experience with the hydrostatic CAM-SE model in CESM (Lauritzen et al., 2018) and the longstanding collaboration between Mark Taylor (Sandia National Laboratories), Peter Lauritzen (NCAR), and the PI Jablonowski (UM). By importing DoE’s nonhydrostatic SE-NH dynamical core from DoE's Earth system model E3SM into CAM it will be possible to run CESM applications at nonhydrostatic scales and retain the current CESM-CAM-SE workflow. The nonhydrostatic dynamical core will be imported into CAM-SE as an option so that the infrastructure already built for the hydrostatic SE can largely be reused. The latter incorporates the physics-dynamics coupling layer, initialization code, grid definition code, I/O, and other functionality. NSF StormSPEED will also closely consult with the EarthWorks team (from Colorado State University & NCAR) to define suitable CAM physics configurations and tuning parameters for kilometer-scale (3-4 km mesh) configurations.