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Modelling the global distribution and climate effects of ice-nucleating particles

Prof Ben Murray (SEE), Prof Ken Carslaw (SEE)

Contact email: b.j.murray@leeds.ac.uk

The formation of ice in clouds is one of the least well understood aspects of the planet’s climate system. Special aerosol particles, known as ice-nucleating particles (INPs), are needed to trigger ice formation in supercooled water clouds but their sources, characteristics and distribution around the globe are very poorly defined. While we have improved our understanding of some INP types, such as desert dust, our understanding of the global distribution of biological INP from terrestrial sources remains extremely poor. In this PhD project you will focus on improving global models of INP and the results will be used to explore the effects on climate.

A cloud growing out of a very dusty lower atmosphere. This aerosol contains INP some of which will be biological. But the global distribution of many INP types, such as biological INP, remains poorly defined.

This PhD project benefits from a collaboration between the Ice Nucleation group and the Aerosol Modelling group. You will use fundamental information from the basic laboratory work and field work from the Ice Nucleation group in order to define the global distribution of new as yet undefined INP sources. You will make use of an existing global model (GLOMAP) in which we already represent INP from deserts and sea spray sources (Vergara-Temprado et al., 2017). You will also have the opportunity to test the effect of the INPs in cloud and weather models in collaboration with the UK Met Office, enabling the research to feed through to an improved understanding of weather and climate.

Objectives

The overall aim of this project is to accurately model the global distribution of INP types. This will be achieved by:

  1. Collating the available atmospheric INP concentration data from around the world in order to identify regions where we are missing INP sources.  There is a revolution going on at the moment in the amount of INP data being generated and you will use this new resource.  For example, the Leeds group have recently shown that there is a large biological INP component in the atmosphere of the UK, which is not represented in our current model.
  2. Develop emission schemes linking emissions to key variables. For example, use local wind speeds and satellite products of local snow cover in glacial valleys to model dust emissions.
  3. Implement these emission schemes in the GLOMAP model and/or a detailed regional model, and test the resulting INP concentrations against measurements.
  4. Model possible anthropogenic impacts on the INP population.  For example, Patagonian dust emissions are thought to have increased dramatically over the last century or so due to farming activities, but we do not know what the impact of this is.
  5. Use the new INP emissions to define INP concentrations in a detailed weather model (the Met Office’s Unified Model with detailed (CASIM) microphysics).  This will allow the representation of both the sources of INP in the atmosphere as well as their sinks through interaction with cloud.  It will also allow you to test the impact of your INP emission schemes on weather and climate.
Dust emissions from Iceland.  These emissions are not currently represented in our model, but high latitude emissions may be very important for the INP budget.

Background

Atmospheric ice-nucleating particles (INP) are aerosol particles with special physical and chemical properties that enable them to induce the formation of ice crystals in clouds below 0°C. In the absence of INP, cloud droplets can supercool to below -33°C. Formation of ice in clouds is a fundamental process that initiates most of the global precipitation. It also has profound effects on the radiative properties of clouds and thereby influences the effect that clouds have on climate.

Despite decades of research on INP, our understanding of INP sources in the atmosphere, and hence their impact on climate, is in its infancy. Substantial developments are being made by characterizing INP in innovative laboratory and field experiments, and then carrying this new knowledge into atmospheric models. For example, the Leeds group discovered that a specific mineral group in desert dust particles can explain their ice nucleating properties, enabling a global model of these INP to be developed (Atkinson et al., 2013). Similarly, we quantified marine organic INP through field measurements in remote environments from research ships and then used our global model to represent the global distribution of these INP (Wilson et al. 2015; Vergara-Temprado et al. 2017).  We now want to extend this model to include other INP types.

There are a numerous aerosol types which are known to nucleate ice.  We have shown that feldspar in desert dust and marine organic associated with sea spray are two of the most important INP types around the globe.  Terrestrial biological materials are some of the most effective materials for nucleating ice that we know of.  For example, certain fungus and bacteria species have evolved the capacity to produce proteins which nucleate ice just below 0°C.  These materials, or more likely fragments of these materials (O’Sullivan et al. 2015), have long been suggested to be important in the atmosphere.  But, it is only recently that we have started to show how important they are relative to materials such as desert dust. Another poorly quantified INP type is high latitude dust.  Current models generally only include dust emissions from the major deserts of the world, mainly in African and Asia.  But, it is known that dust can be emitted at high latitudes from places like glacial valleys in Iceland or Greenland.

Methodologies

The key modelling tools are

  1. The Global Model of Aerosol Processes (GLOMAP: http://www.see.leeds.ac.uk/aerosol) which was developed in Prof Carslaw’s group.  This is a highly advanced model that simulates the global formation, transport and removal of aerosol particles in the atmosphere. It has been used to study a very wide range of aerosol phenomena, including INP (Vergara-Temprado et al. 2017). You will also make use of new laboratory and field measurements of INP properties from Prof Murray’s group in order to develop new descriptions of INP emissions in GLOMAP.
  2. The Met Office’s Unified Model with detailed (CASIM) microphysics.  This state of the art high resolution weather model will allow you to explore the effects of INP on weather and climate (see for example Grosvenor et al.2017).

Requirements

Undergraduate training in any physical/chemical science, computing, mathematics or applied statistics would be appropriate.

Training

Students will receive training in running and visualizing global model results. The aerosol group has a dedicated research and support scientist who leads the technical aspects of the model development as part of the institute’s new Centre of Excellence for Modelling the Atmosphere and Climate (CEMAC).

Co-supervision will involve regular meetings between all partners. In addition the successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of supportive workshops in skills such as managing your degree to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).  There will also be opportunities to take part in field campaigns, international conferences, and training courses offered by other organisations such as the Aerosol Society.

Potential for high impact outcome

Ice nucleation remains a major limitation in our quantitative understanding of clouds in the climate system and new discoveries in this area have the potential to alter the way many scientists think about clouds. We have a strong track record of producing high impact papers with two articles in Nature in the last few years alone.

References

Atkinson, J. D., and Coauthors, 2013: The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds. Nature, 498, 355-358.

Grosvenor, D. P., Field, P. R., Hill, A. A., and Shipway, B. J.: The relative importance of macrophysical and cloud albedo changes for aerosol-induced radiative effects in closed-cell stratocumulus: insight from the modelling of a case study, Atmos. Chem. Phys., 17, 5155-5183, 2017.

Murray, B. J., D. O'Sullivan, J. D. Atkinson, and M. E. Webb, 2012: Ice nucleation by particles immersed in supercooled cloud droplets. Chem. Soc. Rev., 41, 6519-6554.

O'Sullivan, D., Murray, B. J., Ross, J. F., Whale, T. F., Price, H. C., Atkinson, J. D., Umo, N. S., and Webb, M. E.: The relevance of nanoscale biological fragments for ice nucleation in clouds, Scientific Reports, 5, 2015.

Wilson, T. W., and Coauthors, 2015: A marine biogenic source of atmospheric ice-nucleating particles. Nature, 525, 234-238.

Vergara-Temprado, J., Murray, B. J., Wilson, T. W., O'Sullivan, D., Browse, J., Pringle, K. J., Ardon-Dryer, K., Bertram, A. K., Burrows, S. M., Ceburnis, D., DeMott, P. J., Mason, R. H., O'Dowd, C. D., Rinaldi, M., and Carslaw, K. S.: Contribution of feldspar and marine organic aerosols to global ice nucleating particle concentrations, Atmos. Chem. Phys., 17, 3637-3658, 2017.

Further reading

Short articles generally about the importance of ice nucleation and what makes a good ice nucleating particle:

Murray, B. J.: Cracking the problem of ice nucleation, Science, 355, 346-347, 2017.

Russell, L. M.: Atmospheric science: Sea-spray particles cause freezing in clouds, Nature, 525, 194-195, 2015.

Related undergraduate subjects:

  • Applied mathematics
  • Astronomy
  • Atmospheric science
  • Chemical engineering
  • Chemistry
  • Earth science
  • Earth system science
  • Engineering
  • Environmental science
  • Geography
  • Meteorology
  • Physical science
  • Physics