Variabilité du volume d'eau chaude et de la couche barrière de sel dans l'océan Pacifique équatorial à l'échelle interannuelle (ENSO)

Abstract : The Equatorial Pacific is a key region for the El Niño Southern Oscillation (ENSO) phenomenon which strongly influences the global climate variability at the interannual time scale. To improve our understanding of ENSO, the present work aims at a) studying the role of equatorial waves on the Recharge/Discharge (RD) mechanism for ENSO, and b) documenting and analysing salinity barrier layers (BL) in the western Pacific warm pool. The RD mechanism for ENSO is first reviewed from the literature, and then analyzed within 5°N-5°S in using 1992-2006 altimeter-derived sea level anomalies (SLA) and in-situ observations. Changes in the volume of warm water above the thermocline (WWV) within 5°N-5°S, characterizing the RD of the equatorial band, are computed from SLA. The WWV changes appear to be a residual of incoming and outgoing warm waters, resulting from the opposite effects of zonally-integrated meridional Ekman and geostrophic transports of warm water. For the first time with observations, we evidence first baroclinic first meridional mode equatorial Rossby waves to be responsible for the anomalous meridional geostrophic transports of warm water, in changing the basin-scale zonal pressure gradient. Major features of the BL in the equatorial portion of the Western Pacific Warm Pool (WP) are brought to light through analysis of an unprecedented collection of temperature and salinity profiles derived from Argo floats during the period 2000-2007. The co-variability between Barrier Layer Thickness (BLT), sea surface salinity front, sea surface temperature and dynamic height anomalies, highlights clear relationships between BLT and each of those climatic variables. Statistics indicate that thick BL form preferentially under low wind conditions, heavy precipitation, eastward advection of low SSS, zonal current vertical shear, and/or in conjunction with equatorial downwelling Kelvin and Rossby waves (favouring the vertical stretching of the upper water column).
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Christelle Bosc. Variabilité du volume d'eau chaude et de la couche barrière de sel dans l'océan Pacifique équatorial à l'échelle interannuelle (ENSO). Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2008. Français. ⟨tel-00444416⟩

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