Simulations of Global Impact of Dust Speciation on Mixed-Phase Clouds Through Ice Nucleation

Mineral dust can affect climate directly by scattering and absorption of radiation (both solar and terrestrial), and indirectly by modifying microphysical and radiative properties of clouds acting as cloud condensation nuclei (CCN) and ice nuclei (IN). Dust radiative and ice nucleation properties depend on its mineralogical composition. In this study, an online dust mineralogy is developed in the Community Atmospheric Model (CAM5) by the separate prediction of dust components (illite, kaolinite, montmorillonite, hematite and clay/silt). The ice nucleation efficiency of immersion and contact freezing of cloud droplets in mixed-phase clouds are explicitly linked to the dust components (kaolinite and montmorillonite). Sensitivity experiments with CAM5 are performed to investigate the impact of dust mineralogy by assuming all dust having the same ice nucleation efficiency as kaolinite or montmorillonite. Indirect forcing on mixed-phase clouds is examined resulting from the change of dust from pre-industrial time to present-day by the coating of anthropogenic aerosol species.