ENSO connections and processes

Lead Research Organisation: University of Cambridge
Department Name: Applied Maths and Theoretical Physics


The El Niño Southern Oscillation (ENSO) phenomenon is the largest source of year-to-year variability in the climate system. ENSO events are caused by natural ocean-atmosphere interactions in the tropical Pacific, but their impacts are transmitted globally through so-called teleconnections linking distant areas. Teleconnections act through changes in the atmospheric circulation, and they cause regional climate disturbances that can be very damaging, such as floods and droughts. Although Europe is far from the Pacific centre of action, ENSO is also a factor in UK/Europe climate variability. The ENSO cycle has warm (El Niño) and cold (La Niña) phases with largely opposite physical impacts. Recent studies have demonstrated that there is also more than one type of ENSO, depending on location within the equatorial Pacific region, and that teleconnection effects differ from one type to another. Further information about these differing effects, and the underlying processes, is required to improve the prediction of the consequences when an ENSO event arises.

The aim of the work in this proposal is to investigate ENSO and teleconnections by (a) analysing data from observations and realistic climate models, with the use of mathematical methods to determine various 'modes' for ENSO evolution and associated atmospheric changes, and by (b) carrying out numerical experiments with simplified atmospheric circulation models to study the dynamical interactions induced by ENSO-like forcing of the system. Although simplified models are less realistic, by reducing the physical mechanisms represented in such models attention can be focussed on particular dynamical processes and causes and effects which are nevertheless relevant to actual climate variability. The simplified model experiments also provide an opportunity to test the strengths and weaknesses of the analysis methods used in (a).

The results will help us to understand why teleconnection effects may differ from one ENSO event to another, and how processes in the tropics and extratropics are inter-related. An important potential benefit is that long-range forecast producers will be able to check whether the relevant pathways are properly represented in the systems used to predict ENSO and its impacts: accordingly the Met Office is a partner in this project through the monthly-to-decadal forecast group.

Planned Impact

Several long-range forecast centres (Met Office and ECMWF within UK, and similar centres worldwide) produce and issue predictions of world-wide seasonal climate variations at lead times of several months, using complex numerical ocean-atmosphere-land models. The prediction systems are under continual development and assessment, with performance with regard to ENSO and ENSO-related variability - the dominant mode of year-to-year climate fluctuations - being a key indicator. These centres will benefit from the findings of the proposed research on ENSO connections through:
... new methodology for performance assessment, and new insight into the dynamics of ENSO connection processes, that could inform system development;
... new information on varying effects of different ENSO types that could affect the confidence placed in seasonal climate outlooks for specific regions, including UK/Europe.

Seasonal climate predictions are used by a diverse community of 'end-users' in for example energy, agriculture, and health sectors, for local and regional forward planning and risk management. Many of these uses relate to ENSO impacts. Actions are often based on 'typical' impacts estimated by combining all types of events, supplemented in some (but not all) cases by direct regional long-range forecast information. The results of this project will indirectly benefit this community of end-users, and through their actions the quality of life of the public at large, through better understanding of the effects of different ENSO types and through improved regional long-range forecasts.

The general topic of the proposal - ENSO and climate variability - is suitable for a 'popular science' presentation for the general public/schools, and an activity of this kind at the annual Cambridge science festival is proposed in 'pathways to impact'. By this means the project will help raise public awareness of a major climate feature that often has widespread 'headline' impacts.


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Davey M (2016) Fluid and Solid Mechanics

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Rupp P (2020) Spatio-temporal stability analysis applied to monsoon anticyclone flow in Quarterly Journal of the Royal Meteorological Society

Description ENSO events in the tropical Pacific influence the atmospheric circulation world-wide through physical processes known as teleconnections. There are different types of ENSO events, and research in this grant has involved exploration of how the basic structure of the atmosphere influences the teleconnections associated with different ENSO types. Results show differing roles for zonal-average and wave-like features and processes in the atmosphere.
The situation is made more complicated by the wide range of variability in the atmosphere, which means similar ENSO events occurring in different years can have somewhat different impacts. A method has been developed for exploring these effects in a model atmosphere simulating many closely controlled ENSO events. Over the period 2016-17 analyses of further experiments using an atmospheric general circulation model have shown how the superposition of linear and nonlinear teleconnection responses to ENSO-like forcing can generate a complicated pattern of regional changes. A systematic impact of tropospheric forcing on equatorial stratospheric jets has also been found, which has led to a new line of enquiry to seek an explanation of the process.
Exploitation Route The effect of atmospheric structure on ENSO teleconnections means that such structures need accurate representation in long-range forecasting systems, so system developers should place extra emphasis on reducing biases in, for example, the Walker cell in the tropics.
Work continues on analysing the zonal-average and wave-like processes in the data produced during the grant, and this should lead to further process-based diagnostics for use in climate model development.
Sectors Environment

Description With regard to the role of atmospheric variability on ENSO impacts, related to this grant, diagnostics of ENSO effects that have a probabilistic viewpoint have been introduced into the Met Office climate model assessment system. (The researcher working on the project has a part-time post at the Met Office.) Over the period 2016-17 the diagnostics of ENSO impacts implemented in the Met Office climate model assessment system continue to be applied to new versions of the models.
First Year Of Impact 2016
Sector Environment
Impact Types Policy & public services

Description "El Niño: what on earth will happen next?" -- public talk as part of Cambridge Science Festival 2015 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact The talk was presented by Dr Michael Davey as part of the annual Science Week Festival programme at Centre for Mathematical Sciences. It was well attended and has prompted blog comments and an invitation to give a talk at a school (which was taken up).
Year(s) Of Engagement Activity 2015
URL http://talks.cam.ac.uk/talk/index/58121
Description Day School 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact A University of Cambridge Institute of Continuing Education course in February 2017 entitled 'Understanding Climate Variability', with the stated aim that 'participants will learn about some major features of the climate system that influence variability from year-to-year, and their impacts. They will gain an understanding of the underlying physical processes, and find out how useful predictions can be made for seasons ahead'. There were four sessions, entitled 'observed climate variability and climate models', 'El Niño and other climate phenomena', 'impacts', and 'long-range prediction'.
Feedback afterwards indicated that an appreciative audience had learned a lot about what is known about the climate system and how it works, and how forecasts are made and used. There was clear interest in having another related course arranged next year.
Year(s) Of Engagement Activity 2017
URL https://www.ice.cam.ac.uk/courses/short-courses-madingley-hall
Description article for on-line magazine Plus on 'El Niño: What on Earth will happen next?' 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact An article on El Nino was written for Plus Magazine. Plus Magazine is part of the Millennium Mathematics Project, a long term national initiative based in Cambridge and active across the UK and internationally. The MMP aims to help people of all ages and abilities share in the excitement of mathematics and understand the enormous range and importance of its applications to science and commerce. It works to change people's attitudes to maths, to act as a national focus for renewing and improving appreciation of the dynamic importance of maths and its applications, and to demonstrate the vital contribution of maths to shaping the everyday world.
Year(s) Of Engagement Activity 2015
URL https://plus.maths.org/content/el-nino-what-earth-will-happen-next