Daniel Knopf (School of Marine and Atmospheric Sciences, Stony Brook University, NY, USA)

Atmospheric ice formation is considered one of the grand challenges in the atmospheric sciences. Ice crystal 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 descriptions play in interpreting experiments and model simulations. Ice nucleation is often described by a deterministic (non-time dependent) approach, contrary to classical nucleation theory (CNT) that accounts for the stochastic nature of nucleation. These different viewpoints are discussed by looking at immersion freezing and deposition ice nucleation experiments and aerosol-ice formation closure exercises. The impact of freezing parameterization choice on INP and ice crystal budgets is demonstrated by application to a 1D large eddy simulation informed aerosol-cloud model, probabilistic particle‐based (super‐droplet) cloud microphysics model, and gravity-wave induced cirrus formation. 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.

Daniel Knopf is interested in the cloud formation potential and multiphase chemical kinetics of aerosol particles. Daniel pursues this research by means of laboratory experiments, field measurements, and modeling studies. He has advanced the application of nanoscale single-particle analytical techniques to study the phase transition of aerosol particles. Daniel Knopf is a full professor at the School of Marine and Atmospheric Sciences with an affiliated appointment at the Department of Chemistry at Stony Brook University, New York. He received his Ph.D. from the Swiss Federal Institute of Technology and his M.Sc. in physics from the Max Planck Institute for Nuclear Physics/Ruprecht-Karls University of Heidelberg.