Atmospheric implications for mixed stochastic-singular models of ice nucleation

 

Authors

Raymond A Shaw — Michigan Technological University
Dennis Niedermeier — Leibniz Institute for Tropospheric Research
Susan Hartmann — Leibniz Institute for Tropospheric Research
Frank Stratmann — Leibniz Institute for Tropospheric Research
Heike Wex — Leibniz Institute for Tropospheric Research

Category

Aerosol Properties

Description

In the soccer-ball model each ice nucleating particle is envisioned to have a surface divided into a number of surface patches or sites (panel A). Each surface site is associated with a nucleation energy barrier, represented through the contact angle. Contact angles are drawn from a distribution function that holds for the ensemble of particles (panel B). The mean and standard deviation of the contact angle distribution can be inferred from measurements.
Evidence exists that heterogeneous ice nucleation can be described by mixed stochastic-singular models. Recently, for example, our group introduced a “soccer-ball model” that envisions particles made up of surface sites or patches with different nucleation barriers. The key assumption is that classical nucleation theory applies on each patch. The number of patches on a particle and the distribution of nucleation barriers (parameterized through the contact angle) can be varied independently, and therefore the model can describe the transition from purely stochastic behavior to nearly idealized singular behavior. We review some recently published measurements in the context of the soccer-ball model and consider the degree to which model parameters can be fitted unambiguously. This, in turn, allows us to consider some general implications of extending laboratory measurements to the atmosphere, especially when those measurements are interpreted in the stochastic or singular limits.