At TROPOS laboratory experiments investigating nucleation and growth of single ice particles are carried out. Aim of the study is to improve the understanding of the dynamical ice particle growth process as well as the characterization of optical scattering properties of ice crystals in dependence of the prevailing thermodynamic conditions and the type of the ice nucleus (IN). Such an improved knowledge would allow to derive parameterizations for numerical models, and further help to better quantify the indirect climate effect of atmospheric aerosols.
These investigations are done in collaboration with the University of Hertfordshire (UK), and supported by the European Union (EU) research project EUROCHAMP-2 (funded within the 7th Framework Program, Section “Support for Research Infrastructures – Integrated Infrastructure Initiative”).
The experiments are carried out at a laminar flow tube, which has been connected to a optical ice counter (SID-3 instrument, see Kaye et al., 2008) and an additional optical microscope (Fig.1). Basically, the setup was developed based on the experiences with our laminar flow tube chamber LACIS (Leipzig Aerosol Cloud Interaction Simulator, Stratman et al., 2004). But in contrast to LACIS a single fixed ice nuclei (IN) of 5-10 micrometer size is investigated here instead of the continuous aerosol flow. The particle is placed on a thin glass fiber and the positioned within the optical measuring volume of the SID-3 instrument. Both optical devices together (SID-3, microscope) provide time dependent informations about the size, shape and (optical) surface properties (roughness, Ulanowski et al., 2011; Ulanowski et al., 2012) of the ice crystal.
The experiments are carried out with several different types of particles such as ATD, Kaolinit, Illite and Snowmax). Exemplarily, Fig. 2 shows 2-D light scattering and microscope images of different experiments. It was found that both, the macroscopic shape of the ice crystal as well as its surface properties depend on the type of the IN. Furthermore, the (optical) surface properties may change depending on the growth rate. Generally, (fastly) growing ice crystals form rough ice, while a shrinking tend to result in a decreasing surface roughness. The experiments also show that the absolute size has no influence of the surface roughness.
- P. Kaye, E. Hierst, R.S. Greenaway, Z. Ulanowski, E. Hesse, P.J. DeMott, C. Saunders, P. Conolly: Classifying atmospheric ice crystals by spatial light scattering, Opt. Lett., 33(13), 1545-1547, 2008.
- F. Stratmann, A. Kiselev, S. Wurzler, M. Wendisch, J. Heintzenberg, R.J. Charlson, K. Diehl, H. Wex, S. Schmidt: Laboratory studies and numerical simulations of cloud droplet formation under realistic supersaturation conditions, J. Atmos. Oceanic Technol., 21 (6), 876-887, 2004.
- Z. Ulanowski, E. Hirst, P.H. Kaye, R.S. Greenaway: Retrieving the size of particles with rough surfaces from 2D scattering patterns, 13th Int. Conference on Electromagnetic & Light Scattering. In: Atti Accad. Pelorit. Pericol. Cl. Sci. Fis. Mat. Nat. 89, Suppl. 1, C1V89S1P087, 2011.
- Z. Ulanowski, E. Hirst, P.H. Kaye, R.S. Greenaway: Retrieving the size of particles with rough surfaces from 2D scattering patterns: J. Quant. Spectr. Rad. Trans., 113(18), 2457-2464, doi: 10.1016/j.jqsrt.2012.06.019, 2012.