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Ocean Science An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 4 | Copyright
Ocean Sci., 14, 633-660, 2018
https://doi.org/10.5194/os-14-633-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 11 Jul 2018

Research article | 11 Jul 2018

On the role of the North Equatorial Counter Current during a strong El Niño

David John Webb David John Webb
  • National Oceanography Centre, Southampton, SO14 3ZH, UK

Abstract. An analysis of archived data from the NEMO 1∕12th degree global ocean model shows the importance of the North Equatorial Counter Current (NECC) in the development of the strong 1982–1983 and 1997–1998 El Niños. The model results indicate that in a normal year the core of warm water in the NECC is diluted by the surface Ekman transport, by geostrophic inflow and by tropical instability waves. During the development of the 1982–1983 and 1997–1998 El Niños, these processes had reduced effect at the longitudes of warmest equatorial temperatures and to the west. During the autumns of 1982 and 1997, the speed of the NECC was also increased by a stronger-than-normal annual Rossby wave. The increased transport of warm water by the NECC due to these changes resulted in warm water reaching the far eastern Pacific and appears to have been a major factor in moving the centre of deep atmospheric convection eastwards across the Pacific.

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Results from a high-resolution ocean model show that during the strong El Niños of 1983 and 1998, transport of warm water in the equatorial Pacific was dominated by the North Equatorial Counter Current and not by equatorial Kelvin waves. The results show why the NECC fails to do this in most years and how stronger than normal annual Rossby waves near the Equator can both trigger the El Niño in the western Pacific and help to ensure that the warm water arrives off South America around Christmas.
Results from a high-resolution ocean model show that during the strong El Niños of 1983 and...
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