CESM Design Innovations

In order to make progress toward StormSPEED's ultra-high-resolution (3-4 km) grand challenge, we propose removing the hydrostatic barrier in CESM3's default model configuration with a Spectral Element (SE) dynamical core. We will integrate existing nonhydrostatic extensions of the SE dynamical core into CESM3's Community Atmosphere Model (CAM7) to enable cloud-permitting, coupled CESM simulations. In particular, our project will utilize DoE's nonhydrostatic Spectral Element (SE-NH) dynamical core (Taylor et al. 2020) which has been developed for both Fortran and C++ software infrastructures within DoE’s flagship Earth system model E3SM version 2 (E3SM2v2; Golaz et al., 2022) and the 'Simple Cloud-Resolving E3SM Atmosphere Model' (SCREAM; Caldwell et al., 2021; Donahue et al., 2024). The software infrastructures are optimized for the newest computer hardware generations and include support for accelerators, such as Graphical Processing Units (GPUs), in the C++ version. This ensures that the integration of the nonhydrostatic capabilities is fully consistent with the changes in the High-Performance Computing (HPC) landscape. Because the nonhydrostatic CESM-CAM-SE configuration will primarily be relevant for high- to ultra high-resolution Earth system assessments at cloud-permitting scales (either using locally-refined variable-resolution or globally-refined grids), the acceleration on GPUs is a paramount step towards high integration rates on the forthcoming hybrid CPU-GPU-based HPC systems. It is also paramount to work towards a GPU-enabled physical parameterization package for CESM's atmospheric component CAM. This work is currently under way by the Colorado State University (CSU)/NCAR EarthWorks project, and StormSPEED will leverage their physics contributions. EarthWorks and StormSPEED also contribute to the modernization of the Earth System Modeling Framework (ESMF) which is CESM's coupling infrastructure. The latter needs to be enhanced to accommodate kilometer-scale grid spacing.

StormSPEED as well as EarthWorks lay the groundwork for the scientific Earth system modeling opportunities of the future. We ensure that CESM stays connected to the most recent ultra-high-resolution model developments of the international Earth System Modeling (ESM) community.