Reductions in daily continental-scale atmospheric circulation biases between generations of global climate models: CMIP5 to CMIP6

Abstract

Abstract This study evaluates and compares historical simulations of daily sea-level pressure circulation types over 6 continental-scale regions (North America, South America, Europe, Africa, East Asia, and Australasia) by 15 pairs of global climate models from modeling centers that contributed to both Coupled Model Intercomparison Project Phase 5 (CMIP5) and CMIP6. Atmospheric circulation classifications are constructed using two different methodologies applied to two reanalyses. Substantial improvements in performance, taking into account internal variability, are found between CMIP5 and CMIP6 for both frequency (24% reduction in global error) and persistence (12% reduction) of circulation types. Improvements between generations are robust to different methodological choices and reference datasets. A modest relationship between model resolution and skill is found. While there is large intra-ensemble spread in performance, the best performing models from CMIP6 exhibit levels of skill close to those from the reanalyses. In general, the latest generation of climate models should provide less biased simulations for use in regional dynamical and statistical downscaling efforts than previous generations.