Joint Seminar: Using large ensembles to gain insights into the El Niño Southern Oscillation

Single model initial-condition large ensembles (SMILEs) are a powerful tool for separating internal climate variability and forced climate change. SMILEs consist of individual climate models that have been run many times (20-100) under identical external forcing from slightly perturbed initial conditions. Here, I present work that leverages the power of these tools to investigate the El Niño Southern Oscillation (ENSO), using the new multi model large ensemble archive dataset (MMLEAv2). First, I assess the temporal evolution of ENSO SST variability projections and find large model differences. By assessing the evolution of ENSO variability and the mean state in combination, model differences are reduced, highlighting that the models tend to evolve in the same way on varying timescales. Second, I show examples of other research using SMILEs to obtain a more accurate picture of ENSO. This work involves investigating future predictability of ENSO using a model analogues technique. This technique leverages the ensemble size to select ‘similar states’ to any given initial state and create forecasts. Future ENSO predictability is found to be linked to model dependent changes in ENSO SST variability. There is also increased prediction skill before the spring predictability barrier that comes from including the Atlantic and Indian Ocean basins. This suggests a role for important processes outside the Pacific at longer (6-20 month) lead times. Additionally, I present results investigating the risk of high-rainfall events in Australia. These results show an increased future rainfall variance for neutral years, no change for El Niños and increased rainfall for La Niñas. Finally, I present preliminary results on future changes in ENSO SST variability in new stabilised climate runs. ENSO SST variability is similar in all stabilised runs independent of the warming level at which the climate is stabilised. This is in contrast to the transient response. Overall, I demonstrate the power of SMILEs for investigating highly variable phenomenon such as ENSO.




15:15–16:45 h


Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg


Dirk Olonscheck

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