Abstract:
Atmospheric ice formation impacts the radiative forcing of mixed-phase and cirrus clouds, precipitation, and water vapor transport into the lower stratosphere. This seminar focuses on primary ice production pathways from aerosol particles serving as ice-nucleating particles (INPs) and highlights the role different freezing parameterizations play in interpreting experiments and cloud model simulations. Since the 1950s the community has favored the application of a freezing parameterization that is based on an approximation of the physical nucleation model. This yields a freezing spectrum where INPs are treated as unique particles instead of viewing ice nucleation as a stochastic process. Immersion freezing and deposition ice nucleation experiments will be shown to make the case to consider a stochastic nucleation behavior. The effect of these different freezing parameterizations on INP and ice crystal budgets will be demonstrated by application to a 1D large eddy simulation informed prognostic aerosol-cloud model and probabilistic particle‐based (super‐droplet) cloud microphysics model. We show that different freezing descriptions that represent the ice nucleation experiment equally well can yield orders of magnitude different ice crystal number concentrations when applied to cloud conditions. We conclude with suggesting next steps that advance our understanding of atmospheric ice formation.