Comparison between CMIP6 and CMIP5 models in simulating historical spatiotemporal variations in radiation budgets at the top of atmosphere and the surface

Abstract

Based on Clouds and the Earth’s Radiant Energy System (CERES) Energy Balanced and Filled (EBAF) Dataset Edition 4.1, historical spatiotemporal variations in radiation budgets at the top of atmosphere (TOA) and the Earth surface were compared between Coupled Model Intercomparison Project phase 5 (CMIP5) and phase 6 (CMIP6). Regions with high inter-model variability were identified in two CMIPs. The results show that ensemble means of radiation components, except surface upward longwave radiation in CMIP6 are in better agreement with CERES EBAF 4.1. Except downward longwave radiation at the surface, lower inter-model spread for other radiation components are found in CMIP6. Overestimation in global mean surface downward shortwave is reduced by 1.9 W/m2, and underestimation in global mean downward longwave radiation is reduced by 3.3 W/ m2, in CMIP6. Spatially, larger deviations are found in TOA reflected shortwave and outgoing longwave radiation, as well as surface downward shortwave radiation around the North Pole in CMIP6 compared to CMIP5. Worse simulation is also found in CMIP6 for surface downward longwave radiation around 60°latitudes. In other regions, CMIP6 radiation components agree better with CERES EBAF 4.1 than CMIP5. Regions with relative large inter-model variability for surface downward shortwave and downward longwave radiation shrink from CMIP5 to CMIP6. However, regions with extreme large inter-model variability still keep almost the same for the two components in two CMIPs. Two CMIPs are similar in spatial distribution with large inter-model variability for surface net radiation. Tibet Plateau, equatorial Pacific, tropical rainforest, Arabian Peninsula and Antarctic coasts are important regions with extreme large inter-model variability for simulating radiation budgets at the TOA and the surface by Earth System Models. ww.climatecha