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  Decadal modulation of El Nino Southern Oscillation and its global impacts


   Faculty of Environment

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  Dr A Maycock, Dr P. Forster, Dr Jeff Knight, Dr Yohan Ruprich-Robert  No more applications being accepted  Competition Funded PhD Project (Students Worldwide)

About the Project

Overview

There is a strong demand for seasonal-to-decadal climate predictions in the energy, agriculture and water sectors. The skill and reliability of predictions is crucial for their usability. Long-range weather and climate predictions rely on slowly evolving predictable components. These are often fluctuations, or “modes of variability”, in the ocean that are predictable seasons to years ahead, and imprint signatures on weather and climate in remote regions through atmospheric teleconnections. While much research has addressed the effects of individual modes on climate prediction, an emerging research area is their mutual interactions and associated effects on predictability.

This exciting project will investigate the coupling between modes of climate variability and their effects on seasonal-to-decadal forecast skill. You will work at the intersection between atmospheric and oceanic sciences and develop excellent knowledge of climate processes, developing and running climate models, and advanced statistical techniques. You will work with the Met Office to identify potential areas for improvement of their operational seasonal forecasting system.

The research problem

Teleconnections describe interconnections between climate anomalies at distant locations across Earth. Teleconnections frequently arise through the response of atmospheric circulation to changing oceanic conditions. If these patterns can be accurately forecast, the signals provide a major source of predictive skill in seasonal-to-decadal forecasts (Scaife et al., 2016). Hence, there is a need to identify predictable climate signals and understand their effect on the risk of global climate hazards to improve seasonal-to-decadal predictions.

Most previous research has considered teleconnections arising from modes of variability separately. However, there is growing evidence for coupling between modes of variability and their teleconnections on different timescales (Cai et al., 2019). Some recent studies have speculated Atlantic Multidecadal Variability – a fluctuating pattern in the North Atlantic ocean -- augments the response of the winter North Atlantic Oscillation to El Nino Southern Oscillation, the dominant pattern of year-to-year variability in the tropics (e.g., Zhang et al., 2019; Ivasic et al., 2021). ENSO is a key driver of the NAO and this teleconnection is important for seasonal forecasting of European winter climate. However, questions remain about whether the AMV modulation of the ENSO-NAO teleconnection is robust and whether it can be distinguished from a local AMV impact on the NAO (Simpson et al., 2018). This PhD project will develop a new framework for assessing the AMV influence on the ENSO-NAO teleconnection using state-of-the-art large ensemble climate simulations. This will provide the most comprehensive assessment to date of decadal modulation of ENSO-NAO coupling by the AMV.

Another major research topic has been how ENSO affects climate in remote regions, including the North Atlantic (e.g. Trascasa-Castro et al., 2019). Few studies have considered teleconnections that alter ENSO itself. Recent work at the University of Leeds suggests the warm phase of AMV weakens ENSO on decadal timescales. This project will test this effect in a larger set of climate models and identify whether it is robustly simulated. New model simulations will also be performed to test hypotheses and isolate mechanisms. These experiments will exploit new ‘nudging’ capabilities within a climate model that enable specified regions to be constrained to observations to isolate remote impacts.

To close the loop on Pacific-Atlantic interactions, the third question addressed in the project will be: what are the impacts of the North Atlantic Oscillation on ENSO? The motivation comes from the observation that on seasonal timescales the NAO drives a tripolar pattern in North Atlantic sea surface temperatures through modified air-sea coupling (Deser et al., 2010). This raises the potential for longer-term multidecadal NAO trends to impact on climate outside the North Atlantic, but this is currently unexplored. This project will tackle this new question using a combination of statistical analysis of observations and a similar model experiment design where NAO anomalies are ‘nudged’ and the global response evolves.

The specific objectives of the project will be adapted to fit the interests of the student and to pursue the most promising avenues of enquiry. Specific research objectives could include:

  • Quantify how Atlantic Multidecadal Variability affects the ENSO-NAO relationship including the associated mechanisms; test whether this is robust in climate models.
  • Explore the impact of the AMV on ENSO and its mechanisms via Atlantic-Pacific interactions.
  • Investigate the global impacts of interannual to decadal NAO variability, including potential impacts on ENSO.

These topics offer the potential for innovative cutting-edge research and freedom to expand the research in the direction of your own interests.

Research tools

You will use a combination of observation datasets and modelling tools. The multi-model large ensemble archive comprises simulations from state-of-the-art climate models that have performed hundreds of simulations of the historical period. You will use a novel causal inference-based framework to test the influence of AMV on ENSO teleconnections (Kretschmer et al., 2021). Once you have identified potential teleconnection pathways in the large ensemble simulations, you will perform new simulations to test hypotheses and isolate mechanisms. You will have training in the use of climate models and high performance computing systems, including the Leeds’ ARC4 HPC and Met Office supercomputer.

International network

The supervision team are leading experts in their fields and will provide access to a large network of international activities. You will benefit from being part of the EU CONSTRAIN project, a vibrant international research program involving 13 institutes aimed at reducing uncertainty in climate projections. You will undertake visits to the Met Office's Monthly-to-Decadal prediction group and the Climate Prediction group at the Barcelona Supercomputing Center.

Training and research support

You will join the vibrant and dynamic Physical Climate Change group in the Institute for Climate and Atmospheric Science at the University of Leeds. We meet regularly providing a supportive forum to discuss latest research and ideas.

You will benefit from technical support through the Centre for Environmental Modelling and Computing, access to Met Office models and data through the Leeds-Met Office Academic Partnership, and the Priestley International Centre for Climate.

You will have numerous opportunities to present your research at national and international conferences, as well as attending summer schools and training workshops.

Computer Science (8) Environmental Sciences (13) Mathematics (25) Physics (29)

Funding Notes

This project is in competition for up to 26 fully-funded PhDs for UK, EU, and overseas candidates. Each scholarship will provide full tuition fees, tax-free stipend (£15,609 for 2021/22), and a substantial Research Training and Support Grant, for 3.5 years.

References

Cai et al., Pantropical Climate Interactions, Science, 2019, DOI: 10.1126/science.aav4236
Cai, W., Santoso, A., Collins, M. et al. Changing El Niño–Southern Oscillation in a warming climate. Nat Rev Earth Environ 2, 628–644 (2021). DOI: 10.1038/s43017-021-00199-z
Deser, C., M. A. Alexander, S.-P. Xie, A. S. Phillips, Sea Surface Temperature Variability: Patterns and Mechanisms, Annual Review of Marine Science 2010 2:1, 115-143
Ivasić, S., Herceg-Bulić, I. & King, M.P. Recent weakening in the winter ENSO teleconnection over the North Atlantic-European region. Clim Dyn 57, 1953–1972 (2021). DOI: 10.1007/s00382-021-05783-z
Kretschmer, M., Adams, S. V., Arribas, A., Prudden, R., Robinson, N., Saggioro, E., & Shepherd, T. G. (2021). Quantifying causal pathways of teleconnections, Bulletin of the American Meteorological Society (published online ahead of print 2021).
Trascasa-Castro, P., Maycock, A. C., Scott Yiu, Y. Y., & Fletcher, J. K. (2019). On the Linearity of the Stratospheric and Euro-Atlantic Sector Response to ENSO, Journal of Climate, 32(19), 6607-6626.
Scaife, A.A., Comer, R.E., Dunstone, N.J., Knight, J.R., Smith, D.M., MacLachlan, C., Martin, N., Peterson, K.A., Rowlands, D., Carroll, E.B., Belcher, S. and Slingo, J. (2017), Tropical rainfall, Rossby waves and regional winter climate predictions. Q.J.R. Meteorol. Soc., 143: 1-11. https://doi.org/10.1002/qj.2910
Simpson, I. R., Deser, C., McKinnon, K. A., & Barnes, E. A. (2018). Modeled and Observed Multidecadal Variability in the North Atlantic Jet Stream and Its Connection to Sea Surface Temperatures, Journal of Climate, 31(20), 8313-8338.
Smith, D.M., Scaife, A.A., Eade, R. et al. North Atlantic climate far more predictable than models imply. Nature 583, 796–800 (2020). DOI: 10.1038/s41586-020-2525-0
Zhang, W., Mei, X., Geng, X., Turner, A. G., & Jin, F. (2019). A Nonstationary ENSO–NAO Relationship Due to AMO Modulation, Journal of Climate, 32(1), 33-43. DOI: 10.1175/JCLI-D-18-0365.1

Where will I study?