Towards New Measurements of Ice-Nucleating Particles in Cirrus Conditions

Measuring the ice-nucleating particles (INPs) that populate the upper troposphere is critical to understanding the climate impact of cirrus clouds. INPs facilitate in-situ cirrus formation and influence the size and number of ice crystals composing these clouds, as heterogeneous nucleation outcompetes homogeneous nucleation at lower supersaturation with respect to ice. The significant logistical challenges and costs associated with upper troposphere measurements render observational data for this region especially scarce. Analysis of cirrus ice crystal residues by Cziczo et al. (2013) point to heterogeneous nucleation by inorganic INPs as their dominant formation mechanism. Despite their postulated importance, very little is known about the nature and global distribution of INPs in the upper troposphere. Developing capability for routine analysis of upper troposphere INPs is therefore crucial for reducing cirrus-driven uncertainties in climate projections. Here we present our plans and progress towards a new lab-based instrument for offline analysis of INPs in cirrus cloud conditions, aimed at improving understanding of the drivers of heterogeneous ice nucleation in the upper troposphere. This custom-built isothermal diffusion chamber, based on the FRIDGE chamber design (Bundke et al., 2008; Schrod et al., 2016), is adapted to allow cirrus conditions to be accessed. Visual detection of ice growth on a substrate in the chamber will enable quantification of INPs retrieved from the upper troposphere via a balloon-borne collector. The electrostatic precipitator (ESP) for INP collection will be deployed alongside the In-situ Balloon-borne Ice Spectrometer (IBIS) which will measure cirrus ice crystal size distributions during balloon flight. Quantification and subsequent analyses of INPs made possible by the isothermal diffusion chamber development will provide new insights into the formation and evolution of cirrus clouds and their climate impacts.

 

References

Bundke, U., Nillius, B., Jaenicke, R., Wetter, T., Klein, H., and Bingemer, H.: The fast Ice Nucleus chamber FINCH, Atmospheric Research, 90, 180-186, 10.1016/j.atmosres.2008.02.008, 2008.

Cziczo, D. J., Froyd, K. D., Hoose, C., Jensen, E. J., Diao, M. H., Zondlo, M. A., Smith, J. B., Twohy, C. H., and Murphy, D. M.: Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation, Science, 340, 1320-1324, 10.1126/science.1234145, 2013.

Schrod, J., Danielczok, A., Weber, D., Ebert, M., Thomson, E. S., and Bingemer, H. G.: Re-evaluating the Frankfurt isothermal static diffusion chamber for ice nucleation, Atmospheric Measurement Techniques, 9, 1313-1324, 10.5194/amt-9-1313-2016, 2016.