Nucleation of Mesospheric Cloud Particles: Model and Laboratory Results

Abstract:

Nucleation of mesospheric ice is assumed to occur on meteor smoke particles (MSP). Classical nucleation theory however includes several insufficiently known parameters when applied to the conditions at the mesopause for heterogeneous nucleation on MSP. This leads to a great uncertainty in the nucleation rate for mesospheric ice particles. By determining the parameters with the largest impact and comparing different theories we identified a possible range of nucleation rates. These nucleation rates were implemented in the Community Aerosol and Radiation Model for Atmospheres (CARMA).
To study the principal effects, CARMA was run in a one-dimensional setup with static background fields and also with dynamically driven fields from the Kühlungsborn Mechanistic Circulation Model (KMCM) for 69°N. The ice particle properties from both runs are compared with observational data from ALOMAR (69°N). We find that while the static background conditions lead to ice particles comparable to those measured by lidar above ALOMAR, the ice particles in the dynamically driven fields do not evolve to detectable populations. To account for the horizontal transport of ice particles, we extended the model to three dimensions and added a tracer algorithm, which enables us to follow the ice particles from their genesis to final evaporation and to analyse the whole life cycle of the ice particles.
The modelling studies are completed by a comparison to initial laboratory results for ice nucleation rates on nanometer sized particles under realistic mesopause conditions.