At EGU this year I will be presenting preliminary results to the second section of my project, which involves using our aerosol diffusion framework to investigate the effect water diffusion has on cloud microphysics, focusing of ice nucleation in the Tropical Tropopause Layer. Below is a quick overview followed by a link to access the poster.
Key findings
- Initial results show that slow diffusion through aerosol particles could inhibit ice nucleation under conditions found in the Tropical Tropopause Layer.
- A cloud parcel model with bin microphysics has been coupled with an aerosol diffusion framework, however further development is needed.
- Slow bulk water transport through atmospheric aerosol particles could provide an explanation for large ice supersaturations observed in the Tropical Tropopause Layer.
Aims
- Develop a cloud parcel model with bin microphysics that incorporates water diffusion and growth through an aerosol shell model.
- Test the sensitivity of the model to water diffusion coefficients under conditions found in the Tropical Tropopause Layer.
- Discuss the possible effects of slow water diffusion on ice nucleation and supersaturations in the Tropical Tropopause Layer.
Background
To quantify the effect of bulk transport through Secondary Organic Aerosols (SOA), water diffusion coefficients have been measured through a variety of techniques. Then mathematical models, which simulate water diffusion have been used to retrieve diffusion coefficients using mixing timescales. A huge variability has been found in published water diffusion coefficients around the glass transition temperature.
Slow water diffusion, associated with ultra-viscous SOA mixtures, could influence the surface properties of these atmospheric particles and their interactions on a microphysical scale with humid air. Although water diffusion effects in subsaturated environments have been found to be insignificant, diffusion processes could still have implications for cloud formation processes under conditions found in the Tropical Tropopause Layer.
In the future, our study will make use of recently published water diffusion coefficients (Lienhard, 2015). However, to begin with we explore the effect of ultra-viscous SOA cloud microphysics using constant diffusion coefficients, particularly focussing on ice nucleation in the Tropical Tropopause Layer.
Link to poster
To access the poster follow this link [1,299KB].
