Calendar Event Details

Donifan Barahona

Affiliation: NASA GSFC, GMAO
Event Date: Tuesday, September 13, 2011

Location: G-133
Time: 11:00 AM

Describing Heterogeneous Ice Nucleation within Large Scale Atmospheric Models

Ice nucleation in the atmosphere proceeds by homogeneous nucleation in cloud droplets and by heterogeneous nucleation on ice nuclei (IN). Homogeneous nucleation occurs only at cold temperatures and heterogeneous nucleation is the only pathway to the formation of ice and mixed-phase clouds at temperatures above 235 K. The concentration of IN is however greatly influenced by aerosol emissions and an accurate representation of heterogeneous ice nucleation in atmospheric models is critical for climate assessment and prediction. Yet laboratory studies, field campaign data, and theoretical predictions usually present conflicting results and a comprehensive theory of heterogeneous ice nucleation is still lacking. This seminar presents a new formulation of the heterogeneous ice nucleation spectrum, i.e., the function linking the ice crystal number concentration to cloud formation conditions and aerosol properties. The new formulation is based on the concept of ice nucleation probability dispersion and explicitly considers the effects of supersaturation, temperature, and the aerosol surface area and contact angle distribution on the ice crystal number concentration. Several characteristic features of heterogeneous freezing can be explained using this approach, reconciling theoretical and experimental results. The new formulation allows the description of field campaign and laboratory data within a unified framework and is used to generate heterogeneous ice nucleation parameterizations suitable for atmospheric modeling studies. 

Posted or updated: Tuesday, September 6, 2011

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