Importance of the Salinity Barrier Layer for the Buildup of El Niño

Christophe Maes Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, Institut de Recherche pour le Développement, Toulouse, France

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Joël Picaut Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, Institut de Recherche pour le Développement, Toulouse, France

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Sophie Belamari Centre National de Recherches Météorolgiques, Météo-France, Toulouse, France

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Abstract

Several studies using sea level observations and coupled models have shown that heat buildup in the western equatorial Pacific is a necessary condition for a major El Niño to develop. However, none of these studies has considered the potential influence of the vertical salinity stratification on the heat buildup and thus on El Niño. In the warm pool, this stratification results in the presence of a barrier layer that controls the base of the ocean mixed layer. Analyses of in situ and TOPEX/Poseidon data, associated with indirect estimates of the vertical salinity stratification, reveal the concomitant presence of heat buildup and a significant barrier layer in the western equatorial Pacific. This relationship occurs during periods of about one year prior to the mature phase of El Niño events over the period 1993–2002. Analyses from a coupled ocean–atmosphere general circulation model suggest that this relationship is statistically robust. The ability of the coupled model to reproduce a realistic El Niño together with heat buildup, westerly wind bursts, and a salinity barrier layer suggests further investigations of the nature of this relationship. In order to remove the barrier layer, modifications to the vertical ocean mixing scheme are applied in the equatorial warm pool and during the 1-yr period of the heat buildup. At the bottom of the ocean mixed layer, the heat buildup is locally attenuated, as expected from switching on the entrainment cooling. At the surface, the coupled response over the warm pool increases the fetch of westerly winds and favors the displacement of the atmospheric deep convection toward the central equatorial Pacific. These westerly winds generate a series of downwelling equatorial Kelvin waves whose associated eastward currents drain the heat buildup toward the eastern Pacific Ocean. The overall reduction of the heat buildup before the onset of El Niño results in the failure of El Niño. These coupled model analyses confirm that the buildup is a necessary condition for El Niño development and show that the barrier layer in the western equatorial Pacific is important for maintaining the heat buildup.

Corresponding author address: Dr. Christophe Maes, LEGOS, IRD, 18 Evenue Belin, 31401 Toulouse Cedex 4, France. Email: Christophe.Maes@cnes.fr

Abstract

Several studies using sea level observations and coupled models have shown that heat buildup in the western equatorial Pacific is a necessary condition for a major El Niño to develop. However, none of these studies has considered the potential influence of the vertical salinity stratification on the heat buildup and thus on El Niño. In the warm pool, this stratification results in the presence of a barrier layer that controls the base of the ocean mixed layer. Analyses of in situ and TOPEX/Poseidon data, associated with indirect estimates of the vertical salinity stratification, reveal the concomitant presence of heat buildup and a significant barrier layer in the western equatorial Pacific. This relationship occurs during periods of about one year prior to the mature phase of El Niño events over the period 1993–2002. Analyses from a coupled ocean–atmosphere general circulation model suggest that this relationship is statistically robust. The ability of the coupled model to reproduce a realistic El Niño together with heat buildup, westerly wind bursts, and a salinity barrier layer suggests further investigations of the nature of this relationship. In order to remove the barrier layer, modifications to the vertical ocean mixing scheme are applied in the equatorial warm pool and during the 1-yr period of the heat buildup. At the bottom of the ocean mixed layer, the heat buildup is locally attenuated, as expected from switching on the entrainment cooling. At the surface, the coupled response over the warm pool increases the fetch of westerly winds and favors the displacement of the atmospheric deep convection toward the central equatorial Pacific. These westerly winds generate a series of downwelling equatorial Kelvin waves whose associated eastward currents drain the heat buildup toward the eastern Pacific Ocean. The overall reduction of the heat buildup before the onset of El Niño results in the failure of El Niño. These coupled model analyses confirm that the buildup is a necessary condition for El Niño development and show that the barrier layer in the western equatorial Pacific is important for maintaining the heat buildup.

Corresponding author address: Dr. Christophe Maes, LEGOS, IRD, 18 Evenue Belin, 31401 Toulouse Cedex 4, France. Email: Christophe.Maes@cnes.fr

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  • Ando, K., and M. J. McPhaden, 1997: Variability of surface layer hydrography in the tropical Pacific Ocean. J. Geophys. Res, 102 , 2306323078.

    • Search Google Scholar
    • Export Citation
  • Battisti, D. S., and A. C. Hirst, 1989: Interannual variability in a tropical atmosphere–ocean model: Influence of the basic state, ocean geometry and nonlinearity. J. Atmos. Sci, 46 , 16871712.

    • Search Google Scholar
    • Export Citation
  • Belamari, S., 2002: Etude du rôle des coups de vent d'ouest dans le déclenchement d'évènements chauds de type El Niño. Ph.D. thesis, Université Paul Sabatier, Toulouse, France, 236 pp.

    • Search Google Scholar
    • Export Citation
  • Belamari, S., J-L. Redelsperger, and M. Pontaud, 2003: Dynamic role of a westerly wind burst in triggering an equatorial Pacific warm event. J. Climate, 16 , 18691890.

    • Search Google Scholar
    • Export Citation
  • Bjerknes, J., 1969: Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev, 97 , 163172.

  • Blanke, B., and P. Delecluse, 1993: Variability of the tropical Atlantic Ocean simulated by a general circulation model with two different mixed layer physics. J. Phys. Oceanogr, 23 , 13631388.

    • Search Google Scholar
    • Export Citation
  • Bougeault, P., 1985: A simple parametrization of the large-scale effects of deep cumulus convection. Mon. Wea. Rev, 113 , 21082121.

  • Cane, M. A., and S. E. Zebiak, 1985: A theory for El Niño and the Southern Oscillation. Science, 228 , 10851087.

  • Cronin, M. F., and M. J. McPhaden, 2002: Barrier layer formation during westerly wind bursts. J. Geophys. Res.,107, 8020, doi: 10.1029/2001JC001171.

    • Search Google Scholar
    • Export Citation
  • Davey, M. K., and Coauthors, 2002: STOIC: A study of coupled model climatology and variability in tropical ocean regions. Climate Dyn, 18 , 403420.

    • Search Google Scholar
    • Export Citation
  • Delcroix, T., and J. Picaut, 1998: Zonal displacement of the western equatorial Pacific “fresh pool.”. J. Geophys. Res, 103 , 10871098.

    • Search Google Scholar
    • Export Citation
  • Delcroix, T., and M. McPhaden, 2002: Interannual sea surface salinity and temperature changes in the western Pacific warm pool during 1992–2000. J. Geophys. Res.,107, 8002, doi:10.1029/ 2001JC000862.

    • Search Google Scholar
    • Export Citation
  • Delcroix, T., C. Hénin, V. Porte, and P. Arkin, 1996: Precipitation and sea surface salinity in the tropical Pacific Ocean. Deep-Sea Res, 43A , 11231141.

    • Search Google Scholar
    • Export Citation
  • Déqué, M., C. Dreveton, A. Braun, and D. Cariolle, 1994: The ARPEGE/ IFS atmosphere model: A contribution to the French community climate modelling. Climate Dyn, 10 , 249266.

    • Search Google Scholar
    • Export Citation
  • Geleyn, J-F., 1987: Use of a modified Richardson number for parameterizing the effects of shallow convection. Short- and Medium-Range Numerical Weather Prediction, T. Matsuno, Ed., Meteorological Society of Japan, 141–149.

    • Search Google Scholar
    • Export Citation
  • Jin, F-F., 1997a: An equatorial ocean recharge paradigm for ENSO. Part I: Conceptual model. J. Atmos. Sci, 54 , 811829.

  • Jin, F-F., 1997b: An equatorial ocean recharge paradigm for ENSO. Part II: A stripped down coupled model. J. Atmos. Sci, 54 , 830846.

  • Latif, M., and M. Flügel, 1991: An investigation of short-range climate predictability in the tropical Pacific. J. Geophys. Res, 96 , 26612673.

    • Search Google Scholar
    • Export Citation
  • Levitus, S., 1982: Climatological Atlas of the World Ocean. NOAA Prof. Paper 13, 173 pp. and 17 microfiche.

  • Li, B., and A. J. Clarke, 1994: An examination of some ENSO mechanisms using interannual sea level at the eastern and western equatorial boundaries and the zonally averaged equatorial wind. J. Phys. Oceanogr, 24 , 681690.

    • Search Google Scholar
    • Export Citation
  • Lindstrom, E., R. Lukas, R. Fine, E. Firing, S. Godfrey, G. Meyers, and M. Tsuchiya, 1987: The Western Equatorial Pacific Ocean Circulation Study. Nature, 330 , 533537.

    • Search Google Scholar
    • Export Citation
  • Lukas, R., and E. Lindstrom, 1991: The mixed layer of the western equatorial Pacific Ocean. J. Geophys. Res, 96 , 33433357.

  • Madec, G., P. Delecluse, M. Imbard, and C. Lévy, 1998: OPA 8.1 Ocean General Circulation model reference manual. Note du Pôle de modélisation Institut Pierre-Simon Laplace 11, 91 pp.

    • Search Google Scholar
    • Export Citation
  • Maes, C., and D. Behringer, 2000: Using satellite-derived sea level and temperature profiles for determining the salinity variability: A new approach. J. Geophys. Res, 105 , 85378547.

    • Search Google Scholar
    • Export Citation
  • Maes, C., G. Madec, and P. Delecluse, 1997: Sensitivity of an equatorial Pacific OGCM to the lateral diffusion. Mon. Wea. Rev, 125 , 958971.

    • Search Google Scholar
    • Export Citation
  • Maes, C., M. J. McPhaden, and D. Behringer, 2002a: Signatures of salinity variability in tropical Pacific Ocean dynamic height anomalies. J. Geophys. Res.,107, 8012, doi:10.1029/2000JC000737.

    • Search Google Scholar
    • Export Citation
  • Maes, C., J. Picaut, and S. Belamari, 2002b: Salinity barrier layer and onset of El Niño in a Pacific coupled model. Geophys. Res. Lett.,29, 2206, doi:10.1029/2002GL016029.

    • Search Google Scholar
    • Export Citation
  • McDougall, T. J., 1987: Neutral surfaces. J. Phys. Oceanogr, 17 , 19501964.

  • Mechoso, C. R., and Coauthors, 1995: The seasonal cycle over the tropical Pacific in coupled ocean–atmosphere general circulation models. Mon. Wea. Rev, 123 , 28252838.

    • Search Google Scholar
    • Export Citation
  • Meinen, C., and M. J. McPhaden, 2000: Observations of warm water volume changes in the equatorial Pacific and their relationship to the El Niño and La Niña. J. Climate, 13 , 35513559.

    • Search Google Scholar
    • Export Citation
  • Morcrette, J-J., 1990: Impact of changes to the radiation transfer parameterizations plus cloud optical properties in the ECMWF model. Mon. Wea. Rev, 118 , 847873.

    • Search Google Scholar
    • Export Citation
  • Perigaud, C., and C. Cassou, 2000: Importance of oceanic decadal trends and westerly wind bursts for forecasting El Niño. Geophys. Res. Lett, 27 , 389392.

    • Search Google Scholar
    • Export Citation
  • Picaut, J., M. Ioualalen, C. Menkes, T. Delcroix, and M. J. McPhaden, 1996: Mechanism of the zonal displacements of the Pacific warm pool: Implications for ENSO. Science, 274 , 14861489.

    • Search Google Scholar
    • Export Citation
  • Rebert, J-P., J-R. Donguy, G. Eldin, and K. Wyrtki, 1985: Relations between sea level, thermocline depth, heat content, and dynamic height in the tropical Pacific Ocean. J. Geophys. Res, 90 , 1171911725.

    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., and T. M. Smith, 1995: A high-resolution global sea surface temperature climatology. J. Climate, 8 , 15711583.

  • Roemmich, D., M. Morris, W. R. Young, and J-R. Donguy, 1994: Fresh equatorial jets. J. Phys. Oceanogr, 24 , 540558.

  • Schopf, P. S., and M. J. Suarez, 1988: Vacillations in a coupled ocean– atmosphere model. J. Atmos. Sci, 45 , 549566.

  • Sprintall, J., and M. Tomczak, 1992: Evidence of the barrier layer in the surface layer of the Tropics. J. Geophys. Res, 97 , 73057316.

    • Search Google Scholar
    • Export Citation
  • Terray, L., 1998: Sensitivity of climate drift to atmospheric physical parameterizations in a coupled ocean–atmosphere general circulation model. J. Climate, 11 , 16331658.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., and P. Delecluse, 1998: An OGCM study for the TOGA decade. Part II: Barrier-layer formation and variability. J. Phys. Oceanogr, 28 , 10891106.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., and R. Lukas, 1992: TOGA COARE: The Coupled Ocean–Atmosphere Response Experiment. Bull. Amer. Meteor. Soc, 73 , 13771416.

    • Search Google Scholar
    • Export Citation
  • Webster, P. J., V. O. Magaña, T. N. Palmer, J. Shukla, R. A. Thomas, M. Yanai, and T. Yasunari, 1998: Monsoons: Processes, predictability, and the prospects for prediction. J. Geophys. Res, 103 , 1445114510.

    • Search Google Scholar
    • Export Citation
  • Wyrtki, K., 1975: El Niño: The dynamic response of the equatorial Pacific Ocean to atmospheric forcing. J. Phys. Oceanogr, 5 , 572584.

    • Search Google Scholar
    • Export Citation
  • Wyrtki, K., 1985: Water displacements in the Pacific and the genesis of El Niño cycles. J. Geophys. Res, 90 , 71297132.

  • Xue, Y., A. Leetmaa, and M. Ji, 2000: ENSO prediction with Markov models: The impact of sea level. J. Climate, 13 , 849871.

  • Yu, X., and M. J. McPhaden, 1999: Seasonal variability in the equatorial Pacific. J. Phys. Oceanogr, 29 , 925947.

  • Zebiak, S. E., 1989: Oceanic heat content variability and El Niño cycles. J. Phys. Oceanogr, 19 , 475486.

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