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Cambridge NERC Doctoral Training Partnerships

Graduate Research Opportunities

Lead Supervisor: Andrew Orr, BAS

Co-Supervisors: Luke Abraham, Chemistry and Tracey Moffat-Griffin, BAS

Importance of the area of research concerned: 
The Antarctic ozone hole has profound impacts on the Southern Hemisphere atmospheric circulation and surface climate. The ozone hole is caused by chemical reactions that take place primarily on the surface of polar stratospheric clouds (PSCs). With the continued implementation of the Montreal Protocol, recovery of the ozone hole is generally anticipated by the end of the century. However, model predictions using coupled chemistry-climate simulations give a large range of estimates of the rate and timing of this recovery. Accurate projections of its recovery are critical as this will further reshape Southern Hemisphere climate by no longer counteracting the effects of increasing greenhouse gases. However, the fact that the results are model dependent indicates that some mechanisms are not properly represented. In particular, to produce accurate simulations of stratospheric ozone depletion, coupled chemistry-climate models must be able to represent PSC formation mechanisms and their attendant ozone-loss chemistry due to localised dynamics such as mountain waves.
Project summary : 
This projects aim is to produce realistic projections of the recovery of the Antarctic ozone hole, and associated changes to the Southern Hemisphere atmospheric circulation and climate, by including the effects of mountain waves on PSC formation in a chemistry-climate model. Mountain waves play a crucial role in the formation of PSCs by producing localised temperature fluctuations (up to 20 K), enabling stratospheric temperatures to fall below the threshold value for PSC formation. However, small-scale mountain-waves are unresolved by global chemistry-climate models, leading to insufficient PSCs. We will thus improve the representation of mountain-wave-induced PSCs in a chemistry-climate model by including a mountain wave parameterisation scheme (which computes the temperature fluctuations due to unresolved waves). The impacts of this on Arctic ozone depletion will also be examined.
What will the student do?: 
Based within a strong research community at the British Antarctic Survey’s headquarters in Cambridge, you will work with a version of the chemistry-climate configuration of the Unified Model (UM) numerical modelling system, which includes the simulation of mountain-wave-induced PSCs. You will evaluate and further improve the representation of PSC formation mechanisms in the model by comparison with satellite measurements, including MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) PSC observations and mountain-wave-induced stratospheric temperature fluctuations detected by the Atmospheric Infrared Sounder (AIRS), as well as radiosonde data. You will use the improved model to produce more reliable projections of both Antarctic ozone recovery and Arctic ozone, and the subsequent impacts on atmospheric circulation and surface climate. The project will involve considerable international collaboration with scientists at Karlsruhe Institute of Technology and Julich Research Centre, Germany, which you will visit for extended periods to work on analysis of the data.
Orr, A., Hosking, J. S., Hoffmann, L., Keeble, J., Dean, S. M., Roscoe, H. K., Abraham, N. L., Vosper, S., & Braesicke, P. 2015. Inclusion of mountain-wave-induced cooling for the formation of PSCs over the Antarctic Peninsula in a chemistry-climate model. Atmospheric Chemistry and Physics, vol., 15, pp. 1071-1086, DOI: 10.5194/acp-15-1071-2015.
Spang, R., and co-authors, 2012. Fast cloud parameter retrievals of MIPAS/Envisat. Atmospheric Chemistry and Physics, vol. 12, pp. 7135–7164, doi:10.5194/acp-12-7135-2012.
Thompson, D. W. J., Solomon, S., Kushner, P. J., England, M. H., Grise, K. M., & Karoly, D. J. 2011. Signatures of the Antarctic ozone hole in Southern Hemisphere surface climate change. Nature Geoscience, vol. 4, pp. 741–749.
You can find out about applying for this project on the British Antarctic Survey (BAS) page.