Impact of dust in PMIP-CMIP6 mid-Holocene simulations with theIPSL model

Abstract. We investigate the impact of reduced dust during mid-Holocene using simulations with the IPSL model. We consider simulations where dust is either prescribed from an IPSL PI simulation or from CESM simulations (Albani et al., 2015). In addition, we also consider an extreme mid Holocene case where dust is suppressed. We focus on the estimation of the dust radiative effects and the relative responses of the African and Indian monsoon, showing how local dust forcing or orography affect atmospheric temperature profiles, humidity and precipitation. Compared to previous simulations with the IPSL model the results show only minor improvements for the mid Holocene simulation over large regions despite the fact that the IPSLCM6-LR version of the IPSL model is in better agreement with modern observations. The effect of dust has little impact on the model-data comparisons. Our analyses confirm the peculiar role of dust radiative effect over bright surfaces such as African deserts compared to other regions due to the change of sign of the dust radiative effect at the top-of-atmosphere for high surface albedo. We also highlight a strong dependence on the dust pattern. In particular the relative dust forcing between West Africa and the middle east impacts the relative climate response between India and Africa and between Africa, the western tropical Atlantic and the Atlantic meridional circulation. Dust patterns should thus receive a wider attention to fully understand the changes in the dust cycle and forcing during mid Holocene.