Lead supervisor: Alison Ming, DAMTP
Co-supervisor: Martin Andrew, MetOffice; Alex Archibald, Chemistry
Brief summary:
Why do ozone fluctuations act as an artificial pacemaker to the beating heart of the atmosphere?
Importance of the area of research concerned:
The Quasi Biennial Oscillation (QBO) is the main source of year to year variability in the tropical stratosphere (Baldwin et al., 2001). It manifests as a pattern of alternating descending winds, with a period of about 28 months, and dominates the interannual variability of this region. It is primarily driven by waves originating in the troposphere. Despite largely being confined to within 10° of the Equator, the impact of the QBO extends to the whole atmosphere (Baldwin et al., 2001; Haynes et al., 2021) down to the surface.
Although the basic theoretical framework that describes how wave processes drive the regular QBO is well understood, the quantitative details and interactions between the different processes are not (Bushell et al., 2020). Whilst an increasing number of climate models are able to formulate some kind of QBO, few state-of-the-art climate models are able to spontaneously generate one and even then, the phase, strength and downward extent differ significantly from observations.
Understanding processes with the QBO and the impact on the rest of the system is central to increasing our confidence in projections of climate change and seasonal predictability.
Project summary :
Recent work by the Butchart et al. team at the Met Office (submitted) has shown that the phase of the QBOs winds synchronises in models which do not have interactive chemistry (e.g., HadGEM3) but does not in others with interactive chemistry (UKESM1). Furthermore, this synchronisation is episodic in some models. This is important since we can no longer consider different realizations of tropical stratospheric variability to be completely independent in models where this synchronisation occurs. The scope of this PhD project is to better understand the interactions of chemistry and dynamics in the tropical stratosphere. The process-based understanding that results from this project will then help with the analysis of how a linearised ozone scheme affects seasonal to decadal prediction in the Met Office models.
What will the student do?:
We propose that investigating this ozone synchronisation problem will provide a starting point for the PhD project. Preliminary calculations suggest that it is possible to use mechanistic models (such as those by Tanii and Hasebe, 2002) alongside the comprehensive model runs to further explore this behaviour. Having investigated this problem, the student will have built the relevant framework to understand ozone-dynamical interactions in the QBO. We then propose to use this framework and the mechanistic understanding gained to analyse the results of the coupled ozone hindcasts (with a linearised ozone scheme) that the Scaife group (MetOffice) is planning to run. The aim here is to now explore the impacts on seasonal predictability.
Tools and frameworks that may be used within this project:
- Analysis of large dataset such as the CMIP6 data archive and statistical analysis of the climate data
-Use of theoretical and numerical mechanistic models to understand QBO behaviour
-Use of climate model to simulate aspects of the ozone- QBO coupling
-Use of machine learning tools to processes large datasets
References - references should provide further reading about the project:
Baldwin, M. P., et al. (2001), The quasi-biennial oscillation, Rev. Geophys., 39( 2), 179– 229, doi:10.1029/1999RG000073.
Bushell, A.C. et al. (2022), Evaluation of the Quasi-Biennial Oscillation in global climate models for the SPARC QBO-initiative. QJR Meteorol Soc, 148: 1459-1489. https://doi.org/10.1002/qj.3765
Haynes P. et al (2021), The Influence of the Stratosphere on the Tropical Troposphere, Journal of the Meteorological Society of Japan. Ser. II, 2021, Volume 99, Issue 4, Pages 803-845, doi:10.2151/jmsj.2021-040
Tanii, R., and Hasebe, F., Ozone feedback stabilizes the quasi-biennial oscillation against volcanic perturbations, Geophys. Res. Lett., 29( 7), doi:10.1029/2001GL013965, 2002.
Applying
You can find out about applying for this project on the Department of Applied Mathematics and Theoretical Physics (DAMTP) page.