Impact of Dust Speciation on Mixed-Phase Clouds Through Ice Nucleation with the Community Atmospheric Model (CAM5)

Mineral dust can affect climate directly by scattering and absorption of solar and terrestrial radiation, 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 and implemented in the Community Atmospheric Model (CAM5) by the separate prediction of eight dust components (illite, kaolinite, montmorillonite, hematite, quartz, calcite, feldspar, and gypsum). The ice nucleation efficiency of immersion and contact freezing of cloud droplets in mixed-phase clouds are explicitly linked to the dust components based on parameterizations derived from the observations. Several CAM5 experiments are conducted to investigate the impact of dust speciation on cloud properties (e.g., cloud water path, cloud fraction) and radiative fluxes. In one experiment, we test the role of ice nucleation by K-feldspar mineral based on the parameterization by Atkinson et al. (2013), and compare it to two other simulations using the mineralogy-independent parameterizations for desert dust (Niemand et al. 2012; DeMott et al. 2010). Modeled IN number concentrations are compared with data obtained from field observations. We specifically examine the impact of dust speciation in the Arctic region.