General atmospheric circulation and precipitation evaluation of next-generation Earth System Models

Climate model evaluation is an essential part of model development because it offers a thorough understanding of the strengths and limitations of specific model components. One of the challenges climate models face is accurately representing precipitation spatial patterns and intensity. This is mainly due to their relatively coarse resolution and the parameterization of various processes, such as atmospheric convection and cloud microphysics. Additionally, the representation of general atmospheric circulation can be incorrect, leading to issues like the misplacement of the Intertropical Convergence Zone (ITCZ) and storm tracks in higher latitudes. In this study, we evaluate the performance of two next-generation Earth System Models (ESMs) developed through the OptimESM project, focusing on how well these models represent precipitation patterns both in tropical regions and on a global scale. Our analysis includes the historical simulations of several ensemble members of the EC-Earth3-ESM-1 and UKESM1.2 ESMs. We compare these models with their CMIP6 ensemble counterparts to determine whether significant improvements have been made and to identify where these enhancements occur around the globe. By utilizing the zonally averaged mass stream function, we identify the main atmospheric circulation cells and assess how effectively the models represent general atmospheric circulation while interpreting the associated precipitation biases.