Ice Nucleation in Mixed-Phase Clouds - Insights from a 3-D Cloud-Resolving Model with Size-Resolved Aerosol and Cloud Microphysics

A 3-dimensional cloud-resolving model the System for Atmospheric Modeling (SAM) coupled with an explicit bin microphysics scheme and a radar-lidar simulator is employed to investigate ice nucleation in mixed-phase clouds. By implementing an aerosol-dependent, and a temperature- and supersaturation-dependent ice nucleation scheme and treating ice nuclei (IN) size distribution prognostically, the link between ice crystal and realistic aerosols (IN) is established to study aerosol indirect effects. The model simulations are extensively compared with in-situ and ground-based radar and lidar measurements obtained from the Department of Energy's Atmospheric Radiation Measurement (ARM) program. The possible ice enhancement mechanisms are examined to explain why ice particle concentrations are larger than IN concentrations in Arctic mixed- phase clouds. We also investigate the impact of IN on the heterogeneous and/or homogeneous nucleation and the consequent cloud properties. In addition, the significance of droplet evaporation as a source of aerosols in the mixed-phase clouds is explored. This study builds a link between aerosols (IN) and ice formation and enhances the understanding of aerosol effects on cloud microphysical properties through ice nucleation.