Rôle de l'Interaction Océan-Atmosphère dans la Variabilité Intrasaisonnière de la Convection Tropicale.

Abstract : Atmospheric tropical convection is strongly modulated at intraseasonal timescales (periods of 20 to 90 days). Ocean may play a critical role in atmospheric convective activity at this timescale. Sea Surface Temperature (SST) variations would indeed perturb surface fluxes and act to destabilise the atmosphere and trigger convection on the large scale. The associated dynamical response would then act to maintain convection at the intraseasonal timescale by enhancing surface heat fluxes. These SST perturbations are primarily linked with mixed layer temperature ones and so depend, as the available energy to maintain the convection, on the mixed layer depth. Observations support this thermodynamical conception of the physical origin of intraseasonal variability that enables to explain its climatological link with the seasonal march of the monsoons. The impact of SST intraseasonal variations on the organisation of intraseasonal convective events is then further explored using ensembles of LMDZ global circulation model simulations. An important part of the SST intraseasonal variability is moreover associated with the formation of diurnal warm-layers as shown by results using a simple diagnostic algorithm forced by ERA-40 reanalysis data. The validation of this approach using in situ measurements of the global SVP drifter network makes possible to use such an algorithm as a parametrisation of diurnal warm-layers in a climate model such as LMDZ. The ability of the LMD model to produce realistic diurnal warm-layers is shown in a first simulation before discussing the effect of such phenomenon on the simulated intraseasonal variability of the convection.
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Sciences de l'ingénieur [physics]. Ecole Polytechnique X, 2007. Français

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Hugo Bellenger. Rôle de l'Interaction Océan-Atmosphère dans la Variabilité Intrasaisonnière de la Convection Tropicale.. Sciences de l'ingénieur [physics]. Ecole Polytechnique X, 2007. Français. <pastel-00002325>




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