Dr Paul J DeMott

Ice phase transitions can be induced by and within certain atmospheric aerosol particles in all clouds that contain regions with sub-freezing temperatures. Ice nucleating particle (INP) impacts on clouds are poorly explored as causes of important aerosol effects on radiation and climate. In cirrus clouds and some cold layer clouds, aerosols acting as INPs may strongly impact cloud radiative properties and atmospheric chemistry due to their control on ice crystal populations, cloud frequencies and cloud area coverage. In other clouds (e.g., convective, orographic, Arctic and Southern ocean clouds), additional effects may result due to the role of INPs in precipitation development and the subsequent distribution of latent heating of the atmosphere. Fundamental investigations are needed to understand which aerosol particles of natural and/or anthropogenic origin determine the initial ice phase composition of clouds, how they do so (ice nucleation mechanisms), and how clouds may impact the distribution and nature of ice nucleating aerosols in the atmosphere. We approach these issues using focused and specialized laboratory and field measurements of ice nucleation (homogeneous and heterogeneous) by atmospheric aerosols, and investigate implications using numerical cloud modeling studies.