Environmental & Climate Sciences Department Seminar

Prediction of ice nucleating particle (INP) number concentrations from ambient aerosol particles represents an urgent and challenging issue when simulating cloud processes in climate models. Immersion freezing, where an INP is engulfed in supercooled water or aqueous solution, is considered the dominant primary ice formation pathway in the atmosphere. How to parameterize immersion freezing for interpretation of ice nucleation experiments and implementation in cloud models is currently debated. I present two schools of thought where one is based on classical nucleation theory involving a stochastic nucleation process, and the other one is based on a deterministic process which assumes that nucleation proceeds at special ice nucleation active sites. Historically, the latter was suggested to approximate the former model. However, the application of these two approaches yields very different outcomes and conceptual insights in immersion freezing and cloud modeling. I will outline these differences using examples taken from the laboratory, field, and cloud modeling. These include: i) immersion freezing experiments of illite mineral dust; ii) results of the first-of-its-kind aerosol-ice formation closure study at the ARM SGP site; and iii) preliminary results from a minimalistic 1D aerosol-cloud model to understand INP reservoir dynamics in mixed-phase clouds. The presentation concludes with a summary and outlook of the next research steps.