Sensitivity of El Niño intensity and timing to preceding subsurface heat magnitude
Despite extensive ongoing efforts on improving the long-term prediction of El Niño-Southern Oscillation, the predictability in state-of-the-art operational schemes remains limited by factors such as the spring barrier and the influence of atmospheric winds. Recent research suggests that the 2014/15 El Niño (EN) event was stalled as a result of an unusually strong basin-wide easterly wind burst in June, which led to the discharge of a large fraction of the subsurface ocean heat. Here we use observational records and numerical experiments to explore the sensitivity of EN to the magnitude of the heat buildup occurring in the ocean subsurface 21 months in advance. Our simulations suggest that a large increase in heat content during this phase can lead to basin-wide uniform warm conditions in the equatorial Pacific the winter before the occurrence of a very strong EN event. In our model configuration, the system compensates any initial decrease in heat content and naturally evolves towards a new recharge, resulting in a delay of up to one year in the occurrence of an EN event. Both scenarios substantiate the non-linear dependency between the intensity of the subsurface heat buildup and the magnitude and timing of subsequent EN episodes.
Additional Information© 2016 The Author(s). This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Received: 17 May 2016; Accepted: 14 October 2016; Published online: 03 November 2016. J.B. gratefully acknowledges funding from the European Commission through a Marie Curie International Outgoing Fellowship (project MEMENTO from the FP7-PEOPLE-2011-IOF call), and from the European Commission and the Catalan Government through a Marie Curie - Beatriu de Pinós Fellowship (project 00068 from the BP-DGR-2014-B call). X.R. acknowledges funding from the European Commission through the CLIMRUN (grant agreement 265192) and EUPORIAS (308291) projects of the 7th Framework Programme for Research, and from the Spanish Government through the PANDORA (CGL2007-63053) project. Support provided by the NSF (grants 0830068 and 0957884), NOAA (grant NA09OAR4310058) and NASA (grant NNX09AN50G) is gratefully acknowledged. Author Contributions: J.B. took the lead role in the design of the study, performed the simulations, analyzed the data and wrote the manuscript. D.P., S.B., B.C., M.G.-D. and X.R. contributed to the discussion of results and to the revision of the manuscript. The authors declare no competing financial interests.
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