Etude du couplage océan-atmosphère associé aux épisodes de pluie intense en région méditerranéenne

Abstract : The Mediterranean coastal areas are prone to torrential rainfall in autumn. The Mediterranean Sea is the major source of heat and moisture for these extreme meteorological events. Generally, an unstable air mass is transported by a strong low-level wind from the sea towards mountainous regions. The convection is then triggered and could stay several hours over the same area, producing locally large rainfall totals and sometimes flood damages.

The sensitivity of these extreme events to the sea surface conditions has been examined based on high-resolution atmospheric simulations (2-3 km) of three heavy rainfall events over Southern France: catastrophic events in Aude (12-13 November 1999), Gard (8-9 September 2002) and Hérault (3 December 2003). Various SST fields have been used in MESO-NH simulations (optimal interpolation of in-situ observations, satellite SST, empirical increase/decrease of SST). The significant impact on the atmospheric convection (intensity and location) of the overall SST value beneath the low-level jet has been highlighted.

We also evaluated the sensitivity to the air-sea fluxes parameterizations by introducing in the MESO-NH surface scheme (SURFEX) two new iterative bulk sea surface parameterizations: the ECUME parameterization including a multi-campaign calibration of the exchange coefficients and the COARE 3.0 algorithm. The main results are a strong decrease of the wind stress and of the evaporation simulated when the bulk iterative parameterizations are used instead of the original MESO-NH parameterization.

As a third part of this study, an air-sea coupled modelling between the MESO-NH model and a 1D oceanic model in Turbulent Kinetic Energy equations was developed in order to study the impact of heavy precipitation and associated strong wind stress on the Mediterranean Sea mixed layer and the feedbacks on the atmospheric convection for the three same cases studied. The results show the oceanic model's robustness under these extreme atmospheric forcing imposed even in costal area. The short-range oceanic response obtained shows a strong deepening of the oceanic mixed layer under the low-level jet and the local formation of internal mixed layers associated with intense rainfall. This kind of response is particularly important for the dynamics of the oceanic mixed layer as for the atmospheric boundary layer.
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https://tel.archives-ouvertes.fr/tel-00248618
Contributor : Cindy Lebeaupin Brossier <>
Submitted on : Friday, February 8, 2008 - 12:03:16 PM
Last modification on : Friday, April 5, 2019 - 8:14:08 PM
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Cindy Lebeaupin Brossier. Etude du couplage océan-atmosphère associé aux épisodes de pluie intense en région méditerranéenne. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2007. Français. ⟨tel-00248618⟩

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