Modélisation de la variabilité climatique de la circulation et des masses d'eau en Méditerranée : impacts des échanges océan-atmosphère.

Abstract : This thesis aims at progressing on key points about the realistic reproduction of the formation and the paths of the Mediterranean water masses, and their variability. For that purpose, several regional oceanic models of the Mediterranean Sea, with different horizontal resolutions, are developped and used. A realistic configuration, representing the interannual variability of the boundary conditions of these models (atmosphere, Atlantic Ocean, rivers, Black Sea) is used to carry out long-term simulations of the Mediterranean for the last 50 years. Two rare events, characterising the decennial variability in the Mediterranean, are studied: the Eastern Mediterranean Transient (EMT) and the Western Mediterranean Transition (WMT). The EMT is a period, at the beginning of the 1990's, during which the main site of dense water formation in the eastern Mediterreanean basin switched from the Adriatic subbasin to the Aegean subbasin. The ability of the long-term simulations to reproduce the sequence of the EMT events is first proved. Among the preconditionning and triggering elements of the EMT suggested in the literature, we show that the main factors are the intense winter fluxes over the Aegean subbasin during winters 1992 and 1993. The realism of the Cretan Deep Water (CDW) formation and propagation during the EMT is then analysed in reference and sensitivity simulations. The spreading of the CDW on the bottom of the eastern Mediterranean is only reproduced with modified atmospheric conditions. The WMT has been starting during winter 2005 in the Gulf of Lions, during which a huge volume of Western Mediterranean Deep Water (WMDW) was formed with unusual high temperature and salinity. The simulations reproduce the intensity of the winter 2005 deep convection in the Gulf of Lions, which is due to the strong surface buoyancy loss. They also show that 100-km width deep cyclonic eddies are responsible for the fast southwards spreading of the new WMDW. Then, the long-term simulations allow to set back the WMT in the decennial variability of the north-western Mediterranean. They show that the EMT potentially doubled the volume of new WMDW formed in winter 2005 in the Gulf of Lions, but that it is not responsible for the high temperature and salinity of the new WMDW. These unusual characteristics are due to the absence of intense convection in the Gulf of Lions during the 1990's, which favours a salt and heat accumulation in the north-western Mediterranean.
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Submitted on : Tuesday, March 6, 2012 - 4:14:07 PM
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Jonathan Beuvier. Modélisation de la variabilité climatique de la circulation et des masses d'eau en Méditerranée : impacts des échanges océan-atmosphère.. Océanographie. Ecole Polytechnique X, 2011. Français. ⟨pastel-00676896⟩

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