Session

DescriptionFortran, the primary programming language underpinning many operational weather and climate codes, was built around the fundamental principle that performance optimisation is left to the compiler. However, to fully utilise modern HPC architectures and GPUs, additional programming paradigms as well as invasive code changes are often needed to efficiently target modern HPC accelerators. While high-level DSLs or C-based abstraction layers like Kokkos and Raja provide a disruptive path to performance portability, for Fortran such abstractions are lacking. This leads to the fundamental question “What the actual FORTRAN can we do to achieve performance portability for complex physical models?” In this minisymposium we continue this ongoing discussion by looking at cross-architecture portability of ecRad, ECMWF’s state-of-the-art operational radiation model. ecRad is actively used in research or operational contexts at various European weather and climate institutions and is written in a modular fashion in modern, object-oriented Fortran. We highlight the complexities and challenges that its numerous compute kernels and several alternative solvers pose, and, together with industrial and academic partners, discuss different strategies towards a maintainable cross-platform adaptation strategy that runs efficiently across different HPC architectures.