Ice Nucleation at Monocrystalline Surfaces

Ice nucleation in clouds has a significant influence on precipitation as well as on the global radiative budget. Therefore, the role of aerosol particles as ice nuclei has been extensively investigated in field measurements and laboratory studies with immersion freezing being identified as one of the main ice nucleation modes. However, it is unclear how surface characteristics of individual aerosol particles relate to the observed ice nucleation properties. A cold stage setup has been used to investigate the influence of different surface types. Experimental results are presented for freezing of droplets on monocrystalline surfaces such as silicon, copper and graphite. These measurements are contrasted with freezing statistics observed for natural surfaces such as mica. The morphology of these surfaces has been investigated with atomic force microscopy to deduce a relation between surface characteristics and the ice nucleation efficiency. For the investigated surfaces, contact angles have been deduced with classical nucleation theory.