Studies of ice nucleation and its implications in earth's atmosphere

Application deadline: 3 February 2017

Introduction:

Whether clouds consist of liquid water droplets, ice crystals or both (also known as the thermodynamic phase of clouds), has a major impact on the their dynamical development, radiative properties and precipitation efficiency. The thermodynamic phase also affects the clouds interaction with the environment as it alters the redistribution of water vapour throughout the atmosphere.

Ice crystal formation, or nucleation, in earth's atmosphere, in the temperature range between 0 and ‑35°C is initiated by aerosol particles acting as heterogeneous ice nucleating particles (so called INPs) and subsequently interacts with many microphysical processes within clouds; hence, it is vital to understand the processes that lead to the formation / nucleation of ice crystals in earth's atmosphere.

There has been a revival of the study of ice nucleation in recent years and great progress has been made in both understanding the many pathways for ice nucleation and in the parametrization of these important processes for inclusion in weather forecasting and climate models. However, such parametrizations, usually derived from experiments or measurements, often underestimate the numbers of ice nucleating particles at relatively high temperatures (-5 to -15°C). This is a crucial regime where primary ice nucleation can often lead to secondary ice multiplication in the cloud and therefore is worthy of further research.

Project Summary:

The PhD project will involve the characterization of surrogates for atmospherically relevant ice nucleating particles, both in terms of their chemical composition and structure and also in terms of their ice nucleating ability. You will use the Manchester Ice Cloud Chamber (MICC), which is a novel facility at the University of Manchester for studying cloud processes

(see http://www.cas.manchester.ac.uk/restools/cloudchamber/). The MICC is a 10 m3 stainless steel chamber, situated on 3 floors of the Simon Building and can be cooled to temperatures from room temperature to as low as -55°C. The chamber will be used to perform quasi-adiabatic expansion experiments to simulate the cooling and super-saturation of moist air that occurs during cloud formation in the real atmosphere. Ice formation on the atmospherically relevant ice nucleating particles will be measured in these experiments and quantified / summarized using a variety of parameterization frameworks / techniques. You will compare your results with complementary experiments by investigate the freezing of super-cooled droplets containing ice nucleating particles on a cold stage.

Differences / similarities between the techniques will be noted and reasons for any discrepancies will be investigated further.

Techniques learned will be in managing large experiments, probe calibration of common instruments used in the field of atmospheric science, data analysis and summary of large datasets, and parametrization of your results. To gain further insight the PhD may be interested in applying numerical modelling techniques to their data to study the processes of ice microphysics in more detail. You will also learn how to communicate your ideas / findings to a variety of audiences.

References:

Emersic, C., J. Connolly, P., Boult, S., Campana, M., & Li, Z. (2015). Investigating the discrepancy between wet-suspension and dry-dispersion derived ice nucleation efficiency of mineral particles. Atmospheric Chemistry and Physics Discussions, 15(1), 887–929. http://doi.org/10.5194/acpd-15-887-2015 

Connolly, P. J., Emersic, C., & Field, P. R. (2012). A laboratory investigation into the aggregation efficiency of small ice crystals. Atmospheric Chemistry and Physics, 12(4), 2055–2076. http://doi.org/10.5194/acp-12-2055-2012 

Connolly, P. J., Möhler, O., Field, P. R., Saathoff, H., Burgess, R., Gallagher, M. W., & Choularton, T. W. (2009). Studies of heterogeneous freezing by three different desert dust samples. Atmos. Chem. Phys., 9, 2805–2824.

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