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Sur la variabilité climatique de la salinité de surface en Atlantique Nord et son lien avec la circulation océanique dans un modèle couple

Abstract : This work focuses on the sea surface salinity (SSS) anomalies behaviour in the Atlantic. We study their var iability at interannual to decadal timescales, their response to the leading modes of atmospheric variabili ty in the North Atlantic and their link to the large scale oceanic circulation. Given the lack of observati ons on sufficiently long periods and at the basin-scale, the work is essentially based on global coupled si mulations. In the first part of the thesis, the dynamics of SSS anomalies is successively analysed in two coupled simu lations under control conditions: the SINTEX run (ECHAM4-OPA8) and the Bergen Climate Model run (ARPEGE-MIC OM). Our results show that, on average, at intraseasonal timescales, the advection by anomalous Ekman curre nts is at least as efficient in forcing SSS anomalies as the freshwater flux. This has been confirmed in th e observations. Once created, the SSS anomalies are quite persistent because they are not damped by the atm ospheric fluxes. This differs from the case of sea surface temperature anomalies. As a result, the SSS anom alies are more strongly influenced by the mean currents and by the geostrophic variability. In fact, those two terms dominate the SSS changes at low frequency over most of the Atlantic basin. Using a calculation of lagrangian trajectories, we could follow the propagation of SSS anomalies along the mean currents for at l east 5 years. The analysis has been done both locally and in response to the leading modes of atmospheric v ariability in the North Atlantic, that are the North Atlantic Oscillation and the East Atlantic Pattern. Th e results are similar. In the second part of the thesis, the variability of the oceanic meridional overturning circulation (MOC) i s analysed in the Bergen Climate Model. The intensification of the deep convection in the North Atlantic hi gh latitudes forces an acceleration of the MOC after about 5 years. The NAO influences the deep convection but its influence on the MOC itself is mostly done through the mechanical action of the wind at the interan nual timescale. In the model, the tropical Pacific influences the low frequency variability of the MOC. El Niño induces positive SSS anomalies in the tropical Atlantic that seem to be advected within about 30 yea rs in the high latitudes of the North Atlantic where they contribute to destabilize the water column.
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Contributor : Juliette Mignot <>
Submitted on : Thursday, March 18, 2004 - 9:51:53 AM
Last modification on : Friday, May 29, 2020 - 4:00:25 PM
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Juliette Mignot. Sur la variabilité climatique de la salinité de surface en Atlantique Nord et son lien avec la circulation océanique dans un modèle couple. Océan, Atmosphère. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00005370⟩

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