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The equatorial undercurrent, meridional overturning circulation, and their roles in mass and heat exchanges during El Niño events in the tropical Pacific ocean

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Abstract

The equatorial undercurrent (EUC), the shallow meridional overturning cells feeding it, and their role in El Niño and decadal variability in the equatorial Pacific are studied using both in situ data and an ocean general circulation model. Using temperature and current data from the TAO/TRITON moorings at the equator, their data gaps are filled and it was shown that continuous time series of mass transport, temperature, depth, and kinetic energy of the EUC could be constructed for the period 1980–2002 with an excellent accuracy. This dataset was analysed and used to validate the output from an oceanic general circulation model (OGCM). The OGCM was then used to find that variations in the strength of the EUC, shallow meridional overturning (pycnocline convergence and surface divergence), and equatorial upwelling had the same variations in mass transport on interannual and longer time scales within the period 1951–1999. These variations are all caused by variations of the zonal wind stress zonally integrated, in agreement with simple linear and steady dynamics theories. Impact of these mass transport variations and of temperature variations on heat budgets in the entire equatorial band of the Pacific and in its eastern part are quantified.

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Acknowledgments

I would first like to thank Joël Picaut (now retired), who followed this work as my Ph.D. advisor, for all his enthusiam and his great knowledge. I would also like to thank in particular B. Blanke for his following of this work and the many productive discussions, M.J. McPhaden, G. Reverdin, and Y. Tourre for their careful lecture of the Ph.D. manuscript (available in line at http://tel.ccsd.cnrs.fr) associated to this work and their precious comments. I would like to thank G. Alory and G. Lorand for the outputs of the OPA model, forced with NCEP winds and with ERS winds, respectively, and G. Johnson for the in situ data for the EUC, used in the present analysis. I would also like to thank PMEL staff for their work on TAO data (available at http://www.pmel.noaa.gov) and for the development of the very useful Ferret software. Support for this work was provided by the French Department of Education, Research and Technology, CNES, IRD and PNEDC.

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  1. Laboratoire d’Études en Géophysique et Océanographie Spatiales (LEGOS), Université Paul Sabatier, 14, avenue Edouard Belin, 31400, Toulouse, France

    Takeshi Izumo

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Izumo, T. The equatorial undercurrent, meridional overturning circulation, and their roles in mass and heat exchanges during El Niño events in the tropical Pacific ocean. Ocean Dynamics 55, 110–123 (2005). https://doi.org/10.1007/s10236-005-0115-1

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