Evaluation of atmospheric circulations for dynamic downscaling in CMIP6 models over East Asia

A comprehensive model assessment on a 6-hourly scale from multiple dimensions is critical for model selection of dynamic downscaling to reduce uncertainties. In this study, we evaluated the performance of 13 models involved in the Coupled Model Intercomparison Project-6 (CMIP6) by comparing the simulated meteorological variables at the pressure levels of 850, 500, and 250 hPa, including 6-hourly air temperature, specific humidity, zonal wind, meridional wind, and geopotential height, to those from the ERA5 reanalysis data for the 1979–2014 period. The results indicated that the CMIP6 models could mostly reproduce the spatial pattern of the climatology. Most models underestimated air temperature and geopotential height while overestimating specific humidity and zonal and meridional wind speeds in the upper troposphere. Additionally, the interannual variability of zonal and meridional wind exhibited a relatively better performance but limited ability for specific humidity at 850 hPa. Regarding the annual and diurnal cycles, CMIP6 models reasonably captured the annual cycle shape, while an overestimation was detected in simulating the diurnal amplitude, notably at 250 hPa. Based on a comprehensive rating index and overall rankings, our findings showed that no single model was identified as suitable for the simulation of any variables and regions. The models performed well for five variables, including MPI-ESM1-2-LR, MPI-ESM1-2-HR, TaiESM1, and UKESM1-0-LL, over East Asia. Then, according to the overall performance of the five variables and model accessibility, the optimal model varied by region and shared socioeconomic pathway (SSP) scenario. The multi-model ensemble mean outperformed individual models over almost all regions when it comes to comprehensive performance. The MPI-ESM1-2-LR and MRI-ESM2-0 models were the best two out of 13 models as lateral boundary conditions applied to seven climate scenarios over East Asia. This study provides valuable scientific references for selecting the optimal CMIP6 models for the projection of dynamic downscaling over East Asia and eight subregions.