Abstract
The recent 2015–16 El Niño was of comparable magnitude to the two previous record-breaking events in 1997–98 and 1982–83. To better understand how this event became an extreme event, we examine the underlying processes leading up to the peak of the event in comparison to those occurring in the 1997–98 and 1982–83 events. Differences in zonal wind stress anomalies are found to be an important factor. In particular, the persistent location of the zonal wind stress anomalies north of the equator during the two years prior to the 2015–16 peak contrasts the more symmetric pattern and shorter duration observed during the other two events. By using linear equatorially trapped wave theory, we determine the effect of these off-equatorial westerly winds on the amplitude of the forced oceanic Rossby and Kelvin wave response. We find a stronger upwelling projection onto the asymmetric Rossby wave during the 2-year period prior to the peak of the most recent event compared to the two previous events, which might explain the long-lasting onset. Here we also examine the ocean advective heat fluxes in the surface mixed layer throughout the event development phase. We demonstrate that, although zonal advection becomes the main contributor to the heat budget across the three events, meridional and vertical advective fluxes are significantly larger in the most recent event compared to those in 1997–98 and 1982–83. We further highlight the key role of advective processes during 2014 in enhancing the sea surface temperature anomalies, which led to the big El Niño in the following year.
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Acknowledgements
This study was supported by the Australian Research Council’s (ARC) through grant number DE130100663, with additional support coming via the ARC Centre of Excellence for Climate System Science. A. S. is supported by Centre for Southern Hemisphere Oceans Research (CSHOR) and the Earth Science and Climate Change Hub of the Australian Government’s National Environmental Science Programme (NESP). GODAS, NOAA-ERSST-V3 and COBE SST data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at http://www.esrl.noaa.gov/psd/. ORA-S4 and HadISST products used in this study were downloaded from the Asia-Pacific Data Research Centre (APDRC) data server (http://apdrc.soest.hawaii.edu/data/data.php). ECMWF ERA-Interim data have been obtained from the ECMWF data server (http://apps.ecmwf.int/datasets/). PEODAS was obtained from Bureau of Meteorology data server (http://opendap.bom.gov.au:8080/thredds/catalogs/bmrc-poama-catalog.html) and the Ssalto/Duacs altimeter products were produced and distributed by the Copernicus Marine and Environment Monitoring Service (CMEMS). The authors would also like to thank one anonymous reviewer for the constructive comments and suggestions, which substantially improved this manuscript.
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Abellán, E., McGregor, S., England, M.H. et al. Distinctive role of ocean advection anomalies in the development of the extreme 2015–16 El Niño. Clim Dyn 51, 2191–2208 (2018). https://doi.org/10.1007/s00382-017-4007-0
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DOI: https://doi.org/10.1007/s00382-017-4007-0