The impact of climate model resolution on simulation results of aerosol climate effects

Climate model reolution, as one of the important factors affecting model simulation results, are not fully understood in terms of their effects on aerosol-cloud interactions. In this study, the Community Atmosphere Model Version 5.3 is run at three horizontal resolutions (2°, 1°, 0.5°) under the 2000 and 1850 aerosol emission scenarios, respectively, to test whether increasing the resolution can improve the simulation capability of climate models, analyze the similarities and differences of aerosol climate effects at different resolutions, and explore the influence of model resolution on the numerical results of aerosol climate effects. The comparison between observations and model results shows that increasing the resolution can significantly improve the model's ability to simulate total cloud cover and cloud shortwave radiative forcing, and the simulation results are closer to observations at 0.5° resolution, while other variables are not significantly improved. The global average aerosol climate effect is more consistent at different resolutions, with an increase in total cloud cover, cloud water liquid path, and enhanced cloud shortwave and longwave radiative forcing, while the cloud droplet effective radius at the top of cloud, surface air temperature and precipitation are reduced. At different resolutions, the zonal mean tendencies of the changes in aerosol optical thickness, cloud water liquid path, surface air temperature, cloud shortwave and longwave radiative forcing caused by the increase in aerosol is similar, but there are differences in magnitude. Furthermore, the variation of precipitation and cloud cover are quite different in the zonal mean tendencies and values, which still have large uncertainties on regional scale. On the global, the annual average of aerosol indirect radiative forcing （AIF） at 0.5° resolution is reduced by 2.5% compared to the results at 1° resolution and by 6.4% compared to the results at 2° resolution. Overall increasing the model resolution can partially improve the model simulation capability but weakens AIF. However, the variation of aerosol-induced clouds and precipitation varies greatly at different resolutions, and there is a large uncertainty.