A comparison of the ice nucleating efficiencies of dust, polluted dust and smoke in mixed-phase clouds based on spaceborne lidar observations

The thermodynamic phase composition of mixed-phase clouds largely determines their radiative properties and therefore their impact on the Earth's climate. Mineral dust aerosols in the Earth's atmosphere have been suggested by previous laboratory studies, field campaigns and modelling simulations to be efficient ice nuclei of natural origin that influence the fraction of ice in mixed-phase clouds. Time correlations of global vertically-resolved cloud thermodynamic phase with individually analyzed dust, polluted dust and smoke frequencies over approximately 5 years (December 1 2007 to December 31, 2012) in the mixed-phase cloud temperature regime were performed on retrievals from NASA's CALIPSO. Our results suggest that it can be seen from space that dust aerosols in the Earth's atmosphere are efficient ice nuclei and furthermore, that dust aerosols in polluted regions tend to be less efficient at ice nucleation, which is also supported by previous studies. In addition, we find that smoke aerosols, like dust aerosols, are also acting as ice nuclei in the Earth's atmosphere, although less efficiently than dust.