Influence of the equatorial deep jets on the north equatorial countercurrent
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An ocean circulation model is run using two different idealized equatorial basin configurations under steady wind forcing. Both model versions produce bands of vertically alternating zonal flow at depth, similar to observed Equatorial Deep Jets (EDJs) and with a time scale corresponding to that of the gravest equatorial basin mode for the dominant baroclinic vertical normal mode. Both model runs show evidence for enhanced variability in the surface signature of the North Equatorial Counter Current (NECC) with the same time scale. We also find the same link between the observed NECC and the EDJs in the Atlantic by comparing the signature of the EDJ in moored zonal velocity data at 23° W on the equator with the signature of the NECC in geostrophic velocities from altimeter data. We argue that the presence of a peak in variability in the NECC associated with the EDJ basin mode period is evidence that the influenceatthis time scale is upward, from the EDJ to the NECC.
KeywordsNorth Equatorial Counter Current Ocean circulation model Equatorial Deep Jets
This study has been supported by the Deutsche Forschungsgesellschaft as part of the Sonderforschungsbereich 754 “Climate Biogeochemistry Interactions in the Tropical Oceans.” We are also grateful for support from the European Union 7th Framework Programme (FP7 20072013) under grant agreement 603521 PREFACE Project and the BMBF SACUS (03G0837A)project, as well as continuing support from GEOMAR. The altimeter products were produced by Ssalto/Duacs and distributed by AVISO, with support from CNES http://www.aviso.altimetry.fr/duacs/. NCEP reanalysis data were provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their website at http://www.esrl.noaa.gov/psd/. We are grateful to François Ascani for his help with the model setup and ongoing discussions on the topic of equatorial deep jets and their representation in models, and also to two anonymous reviewers and the editor for helpful comments.
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