Benguela Niños and Benguela Niñas in forced ocean simulation from 1958 to 2015

Type Article
Date 2019-08
Language English
Author(s) Imbol Koungue Rodrigue Anicet1, 2, 3, Rouault Mathieu2, 3, Illig Serena2, 4, Brandt Peter1, 5, Jouanno Julien4
Affiliation(s) 1 : GEOMAR Helmholtz Centre for Ocean Research Kiel Kiel ,Germany
2 : Department of Oceanography, MARE InstituteUniversity of Cape Town Cape Town South Africa
3 : Nansen‐Tutu Centre for Marine Environmental Research, Department of Oceanography, University of Cape Town Rondebosch ,South Africa
4 : Laboratoire d’Etudes en Géophysique et Océanographie Spatiales (LEGOS), Université de Toulouse, CNES, CNRS, IRD, UPS Toulouse ,France
5 : Christian‐Albrechts‐Universität zu Kiel Kiel, Germany
Source Journal Of Geophysical Research-oceans (2169-9275) (American Geophysical Union (AGU)), 2019-08 , Vol. 124 , N. 8 , P. 5923-5951
DOI 10.1029/2019JC015013
WOS© Times Cited 17
Keyword(s) Benguela Ninos, Benguela Ninas, equatorial Kelvin waves, upwelling, South Atlantic anticyclone

A systematic study of Benguela Niño and Benguela Niña events during 1958 to 2015 including those that developed before the satellite era (1982) is carried out using an ocean general circulation model in combination with a linear equatorial model. Altogether, 21 strong warm and cold anomalous coastal events are identified among which 6 undocumented extreme coastal events are reported. Results suggest that most of these extreme coastal events including the newly identified ones are linked to remote equatorial forcing via mode 2 equatorial Kelvin waves. The latter propagates after approaching the African coast poleward as coastally trapped waves leading surface temperature anomalies along the Angola‐Benguela current system by 1 month. 1‐2 months before the peak of Benguela Niños or Niñas usually occurring in March‐April, a large‐scale wind stress forcing is observed with both local (variations of alongshore coastal wind stress) and remote forcing developing simultaneously. Results further suggest that surface temperature anomalies off Southern Angola and in the Angola‐Benguela Front are associated with equatorial dynamics and meridional wind stress fluctuations off the southwestern African coast north of 15°S. Similar mechanisms are observed for Northern Namibia in combination with forcing by local meridional wind stress variations.

Key points

Over 1958‐2015, we document the development of Benguela Niño and Niña events occurring along the southwestern African coast

They are associated with coastally trapped waves dominantly forced by eastward propagating equatorial Kelvin waves of second baroclinic mode

They are linked to large‐scale wind stress forcing 1‐2 month before they peak usually in March‐April

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