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The impact of polar stratospheric clouds when modelling the future recovery of the polar ozone layer

   Polar Science for Planet Earth

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  Dr A Orr, Dr L Abraham  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Brief summary: 

This project will investigate the impact of a realistic representation of polar stratospheric clouds (PSCs) on model projections of twenty-first century stratospheric polar ozone levels and climate in both hemispheres, with involvement from NASA and other international partners.

Importance of the area of research concerned: 

Polar stratospheric clouds (PSCs) play a crucial role in controlling polar stratospheric ozone depletion, e.g., the Antarctic ozone hole. One important source of PSCs is from negative temperature anomalies induced by vertically propagating wave motion forced by stratified flow over high mountains (i.e., mountain waves), which can result in temperatures falling below the thresholds for PSC formation. However, this formation mechanism is missing in global chemistry–climate models because these temperature fluctuations are neither resolved nor parameterised. This limits our ability to accurately predict the timing of the closure of the ozone hole during the 21st century, which is critical as this will likely lead to a nearly complete cancellation of future summer atmospheric circulation changes in this region associated with increasing greenhouse gases. This project will address these issues by using a global chemistry-climate model with a novel representation of mountain-wave-induced PSCs to develop better projections of future polar ozone levels in response to climate change and to narrow uncertainties in the timing of the closure of the ozone hole and associated climate impacts.

Project summary : 

The UM-UKCA chemistry-climate model includes a scheme describing stratospheric mountain-wave-induced temperature fluctuations, which is coupled to the models PSC scheme. Developments such as this that make interactive chemistry-climate models more physically based and comprehensive are needed to improve our ability to make accurate predictions of stratospheric ozone and reduce uncertainties in the current and future climate. The model will be used to understand the sensitivity of projections of 21st century stratospheric polar ozone levels and climate in both hemispheres to inclusion of realistic representation of PSCs, and especially whether the timing of the recovery of the Antarctic ozone hole (and its role in offsetting the effects of increasing greenhouse gases) is affected. The project will involve close collaboration with an ongoing complementary project between BAS and NASA.

What will the student do?: 

They will use the UM-UKCA model with the mountain-wave-induced temperature fluctuations scheme to do the following: 1) To further improve the representation of PSCs in UM-UKCA, implement a new PSC scheme into the model (which is used by the ICON-ART model) that represents all three PSC types (NAT, STS, and ice) and their associated ozone-destroying chemical reactions. 2) Assess the representation of PSCs in this enhanced version of UM-UKCA by comparing output in both hemispheres from model simulations with “third-generation” PSC satellite-based data products generated by NASA. This will involve collaborating closely with NASA scientists. Comparison with other satellite datasets will also be made. 3) Use the enhanced UM-UKCA model to perform simulations from 1960 to 2100, which will include control experiments with the mountain wave scheme switched off, and perturbation experiments with it switched on. The simulations will be run for a range of future greenhouse gas emissions scenarios and climate change. Differencing output from these model simulations will enable us to quantify the impact of realistic representation of PSCs on projections of polar stratospheric ozone and climate.

Funding Notes

UK students will be eligible for a full NERC studentship. More information is available in the UKRI Training Grant Guide (
A full studentship will include the cost of fees and a maintenance allowance. UKRI have confirmed that international students (EU and non-EU) will be eligible for all Research Council-funded postgraduate studentships from the start of 2021/2022 academic year. There will be a limited number of international studentships available


Orr, A., Hosking, S., Dellon, A., Hoffmann, L., Spang, R., Moffat-Griffin, T., Keeble, J., Abraham, L., and Braesicke, P., 2020. PSCs initiated by mountain waves in a global chemistry-climate model: A missing piece in fully modelling polar stratospheric ozone depletion. Atmospheric Chemistry and Physics, vol. 20, pp. 12,483-12,497,
Thompson, D. W. J, Solomon, S., Kushner, P. J., England, M. H., Grise, K. M., and Karoly, D. J., 2011. Signatures of the Antarctic ozone hole in Southern Hemisphere climate change. Nature, vol. 4, pp. 741-749,
Polvani, L. M., Previdi, M., and Deser, C., 2011. Large cancellation, due to ozone recovery, of future Southern Hemisphere atmospheric circulation trends. Geophysical Research Letters, vol. 38,
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