An advective-reflective conceptual model for the oscillatory nature of the ENSO

Science

Volumn 277, Issue 5326, 1997, Pages 663-666

  Picaut, J ^a   Masia, F ^a   Du Penhoat, Y ^a,b  

^a Groupe SURTROPAC   (New Caledonia)

^b Groupe de Recherche de Géodésie Spatiale GRGS   (France)

Author keywords

[No Author keywords available]

Indexed keywords

ADVECTIVE-REFLECTIVE CONCEPTUAL MODEL; ATMOSPHERE-OCEAN COUPLING; ENSO; OSCILLATIONS;

ARTICLE; ATMOSPHERE; PRIORITY JOURNAL; SEA; WATER TEMPERATURE; WEATHER;

PACIFIC;

EID: 0030868606     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.277.5326.663     Document Type: Article

References (37)

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9. -1) back to the region of positive SST perturbation and counteract its growth.
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20. In our study, the wave guide was defined by the equatorial band where zonal currents induced by equatorial waves were maxima, 4°N to 4°S or less (11). In this band and over the 1986-89 period, there was almost no difference in the zonal displacements of the eastern edge of the warm pool induced by the total zonal surface currents and by the currents restricted to the first baroclinic Kelvin and first meridional Rossby modes (18).
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23. The ocean model covered 130°E to 80°W, 15°N to 15°S, with a 0.5° longitude by 0.125° latitude grid. It was run on a 5-day time step and on an anomaly basis. Dissipation was taken into account in the form of Rayleigh friction. The longitudinal shape of the mean zonal currents was approximated by a simple analytic function, based on drifter observations (34) (Fig. 2B).
24. The observed near coincidence of the eastern edge of the warm pool (defined by the 29°C isotherm) and the oceanic zone of current convergence (19) was explained by the dominance of zonal advection in the displacements of this edge and the presence there of a nearly constant SST gradient (Fig. 1A).
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26. A similar concept of expanding wind and zonal displacement of the eastern edge of the warm pool at the onset of an El Niño has been previously modeled [W. S. Kessler, M. J. McPhaden, K. M. Weickmann, J. Geophys. Res. 100, 10613 (1995)].
27. The size and shape of the wind stress patch were determined from observations (Fig. 1D), with meridional and zonal structures approximated by two gaussian functions. The meridional gaussian function was fixed and centered at the equator with about 7° of exponential decay in latitude. The bandwidth of the zonal gaussian function was variable and was set to the distance from OCEE to the midpoint. The change from a constant westerly to a constant easterly during the shift from El Niño to La Niña or vice versa (that is, when the OCEE crosses the midpoint) was done gradually through a cosine function over 10° to 15° longitude. Knowing that anomalous winds due to SST perturbations were located west of these perturbations (Fig. 1, C and D), we shifted the simulated eastern edge of the wind stress patch westward by 5° to 15° compared with the OCEE.
28. The system will forget this initial westerly wind kick once it is on a perpetual ENSO oscillatory motion.
29. -1 for the mean zonal currents near the western and eastern ocean boundary, respectively (Fig. 2B).
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33. J. Picaut, F. Masia, Y. du Penhoat, data not shown.
34. P. Niiler et al., J. Phys. Oceanogr., in press.
35. W. T. Liu, A. Zhang, J. K. B. Bishop, J. Geophys. Res. 99, 12623 (1994).
36. -1), which is larger than the mean transport of any equatorial currents (16). This implies powerful discharge or recharge of water masses in the equatorial band and therefore strong readjustment of the equatorial thermocline together with meridional transfer of water masses [K. Wyrtki, ibid. 90, 7129 (1985)].
37. We thank P. Waigna for preparing all the figures, M. J. Langlade for help in the processing of several figures, and N. J. Mantua and D. S. Battisti for their authorization to reproduce Fig. 1, C and D. The Florida State University wind stress and SST data were provided by J. J. O'Brien and R. W. Reynolds. Discussions and corrections on an early draft by T. Delcroix, P. Rual, L. M. Rothstein, G. Eldin, A. J. Busalacchi, M. J. McPhaden, and J. P. McCreary are appreciated. Supported by ORSTOM, Programme National d'Etudes de la Dynamique du Climat, and Centre National d'Etudes Spatiales.