Couche melangee oceanique et bilan thermohalin de surface dans l'Ocean Indien Nord

Abstract : The goal of this thesis is to establish the oceanic and atmospheric processes that drive the seasonal and interannual variability of Sea Surface Temperature (SST) in the northern Indian Ocean. To achieve this goal, a forced ocean general circulation model is used and we analyse the oceanic and atmospheric terms that influence the mixed layer temperature, a proxy of SST. The upper ocean layer is of the utmost importance in that study. A correct simulation of the mixed layer depth will give us more reliable results regarding the potentially small variations of SST in that region. The first part of this work is to construct a climatology of the oceanic mixed layer depth from observations. As this product may be useful as well for other part of the ocean, we decide to do it on the global scale. Thanks to an innovative methodology, based on individual oceanic profiles, this new climatology exhibits more details in typical oceanic patterns and less biases than the previous ones. This study also shows the role of salinity on mixed layer depth. In addition to the barrier layer areas, we reveal vertically density-compensated layers in winter in the subtropical gyres and subtropical convergence zone. Some formation mechanisms are proposed for these structures about which little is known.
The investigation of simulated mixed layer heat and salinity budgets improves on the role of the ocean in the regulation of SST in the northern Indian Ocean. Even if wind is an important factor in driving the seasonal cycle of SST, several oceanic processes have an active role in this variability. In summer, in western Arabian Sea, oceanic upwellings contribute to decrease SST and dominate the atmospheric contribution. In eastern Arabian Sea and in the Bay of Bengal, sea surface salinity (SSS) is mainly driven by oceanic currents. Barrier layers created by these surface salinity changes allow to store heat below the surface layer that can be recovered later by entrainment warming during winter. On interannual timescale, in western Arabian Sea, both vertical processes and winds contribute significantly to SST variability. However, mechanisms of SST regulation appear to be more complicated than on seasonal timescale and require a more careful investigation.
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Submitted on : Tuesday, January 24, 2006 - 4:31:24 AM
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Clément de Boyer Montégut. Couche melangee oceanique et bilan thermohalin de surface dans l'Ocean Indien Nord. Climatologie. Université Pierre et Marie Curie - Paris VI, 2005. Français. ⟨tel-00011449⟩

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