From single storms to large-scale waves: a multi-year kilometer-scale global simulation

Abstract. Global kilometer-scale (km-scale) weather and climate models offer new opportunities to unify numerical weather prediction (NWP) and climate modeling by explicitly simulating convection and mesoscale circulations globally within a single modeling framework. We present results from the first multi-year (April 2020–March 2024) global atmosphere-land simulation using the GPU-refactored ICON model at a 2.5 km horizontal grid spacing and 120 vertical levels. The simulation uses NWP physics and observed sea-surface temperatures. We assess its performance against satellite, reanalysis, and in-situ observations using standard statistics and the MOAAP feature-tracking framework to evaluate a wide spectrum of atmospheric phenomena. ICON reproduces global temperature and precipitation patterns, including a realistic single Intertropical Convergence Zone and physically consistent diurnal precipitation cycles. However, ICON exhibits continental summertime warm and dry biases, linked to an overestimation of incoming solar radiation and excessive surface sensible heat fluxes. The model realistically captures the intensity and frequency of hourly precipitation and near-surface winds, as well as the structure and occurrence of tropical cyclones. Mesoscale convective systems (MCSs) exhibit realistic spatial initiation patterns, but their frequency is underestimated over oceans and overestimated over tropical land. Long-lived MCSs are too infrequent and small, while increased rainfall from shallow and mid-level clouds may reflect overactive warm-cloud microphysics or observational deficiencies. These biases might stem in part from a misrepresentation of thermodynamic-convection coupling. Our results demonstrate the feasibility and scientific value of multi-year global km-scale simulations for exploring the weather–climate system and local-scale extreme events, while identifying key directions for future model development.