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Climate Dynamics

, Volume 53, Issue 3–4, pp 2339–2353 | Cite as

Is the boreal spring tropical Atlantic variability a precursor of the Equatorial Mode?

  • Marta Martín-ReyEmail author
  • Alban Lazar
Article

Abstract

The Equatorial Mode (EM) governs the tropical Atlantic inter-annual variability during boreal summer. It has profound impacts on the climate of adjacent and remote areas. However, predicting the EM is one of the most challenging and intriguing issues for the scientific community. Recent studies have suggested a possible connection between the boreal spring Meridional Mode (MM) and the EM through ocean wave propagation. Here, we use a set of sensitivity experiments with a medium-resolution ocean model to determine the precursor role of a MM to create equatorial SST variability. Our results demonstrate that boreal summer equatorial SSTs following a MM, are subject to two counteracting effects: the local wind forcing and remotely-excited oceanic waves. For a positive MM, the anomalous easterly winds blowing along the equator, shallow the thermocline, cooling the sea surface via vertical diffusion and meridional advection. Anomalous wind curl excites a downwelling Rossby wave north of equator, which is reflected at the western boundary becoming an equatorial Kelvin wave (KW). This downwelling KW propagates eastward, deepening the thermocline and activating the thermocline feedbacks responsible for the equatorial warming. Moreover, the local wind forcing and RW-reflected mechanism have a significant and comparable impact on the equatorial SST variability. Changes in the intensity and persistence of these distinct forcings will determine the equatorial SST response during boreal summer. Our results give a step forward to the improvement of the EM predictability.

Keywords

Tropical Atlantic Meridional Mode Equatorial Mode Ocean waves SST variability 

Notes

Acknowledgements

The research leading to these results received funding from the EU FP7/2007-2013 under Grant Agreement 603521 (PREFACE project), the MORDICUS grant under contract ANR-13-SENV-0002-01, CNES/EUMETSAT (CNES—DIA/TEC-2016.8595, EUM/LEO-JAS3/DOC/16/852054) and the MSCA-IF-EF-ST FESTIVAL (H2020-EU project 797236). The observed SSTs from HadISST dataset were provided by the MetOffice Hadley Centre, from its website at https://www.metoffice.gov.uk/hadobs/hadisst/. The data from the INTER, MM-REF, MM-WIND and MM-WAVE simulations are available from the authors upon request.

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Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  1. 1.Laboratoire d’Oceanographie et du Climat: Expérimentation et Approches Numériques (LOCEAN)Université Pierre et Marie Curie (UPMC), Universités SorbonnesParisFrance
  2. 2.UMR5318 CECI CNRS-CERFACSToulouseFrance
  3. 3.Departamento de Oceanografía Física y TecnológicaInstituto de Ciencias del Mar (ICM-CSIC)BarcelonaSpain

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