GPU-accelerated atmospheric chemical kinetics using single precision in the ECHAM/MESSy (EMAC) model v2.55 with MEDINA v2.0

Abstract. Atmospheric chemical kinetics puts a major computational burden on Earth system models, yet its embarrassingly parallel nature of the problem structure makes it well suited to GPU acceleration. Here we present a single-precision floating point (FP32) GPU implementation of the MECCA chemical kinetics submodule in the ECHAM/MESSy Atmospheric Chemistry (EMAC) model. It is enabled by the MEDINA code-to-code compiler v2.0 and compatible with the Rosenbrock-family numerical solvers generated by the Kinetic Pre-Processor (KPP). The approach exploits FP32 arithmetic inside the GPU kernels while preserving double precision in the host EMAC workflow via explicit type conversion on the GPU.

We evaluate the numerical fidelity and achieved performance in both an idealised box-model configuration and in full EMAC production simulations on the JUWELS Booster system. Across tested mechanisms and resolutions, FP32 reproduces the double-precision CPU reference to within <0.004 % in total-species-mass differences, with discrepancies confined to chemically depleted tracers near machine representation limits. In production-scale runs, FP32 further reduces the average chemical-kinetics execution time by about 30 % relative to the FP64 GPU implementation and lowers the memory footprint of FP-intensive data structures. Chemistry calculations in FP32 enhance scalability for high-resolution and chemically complex simulations.