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Rôle de la surface marine sur la variabilité intrasaisonnière estivale de l'atmosphère dans la région Nord Atlantique Europe

Abstract : This PhD aims at assessing if the coupling of the atmosphere with the marine surface plays a role in the summer intraseasonal variability of the large-scale atmospheric circulation and if the marine surface can be a source of potential predictability for the atmosphere on these timescales. A second objective is to analyse the role of representing the ocean diurnal variations on the representation of the sea surface temperatures and the large-scale atmospheric circulation on longer timescales. To conduct this work, the CNRMOM1D 1-dimensional ocean model has been developped : the choice of parametrizations used in this model aims at optimizing the representation of physical processes dominating the evolution of Sea Surface Temperatures (SST) on diurnal to intraseasonal timescales. The results obtained from numerical simulations run with the ARPEGE-climat atmosphere model, forced or coupled with the CNRMOM1D ocean model, suggest that the SST anomalies induced by the large-scale atmospheric circulation produce a negative retroaction on the atmosphere on intraseasonal timescales : the coupling with the ocean surface in the North Atlantic European region reduces the persistence of the summer Atlantic Low, Blocking and NAO- weather regimes by about 1day which amounts to about 15% of their mean persistence. Using CNRMOM1D ocean forced simulations, we show that the correction in daily mean SST induced by the representation of the ocean diurnal variations can reach 0.3°C to 0.5°C. This anomaly can persist about 15 to 40 days in the mid-latitudes, more than 60 in the Tropics. Furthermore, using coupled simulations with the ARPEGE-climat atmosphere model, we show that the ocean diurnal variability can modify the summer mean state by a reduction of the SST meridional gradient, a reduction in sea ice extent, a anomaly in large-scale atmospheric circulation that projects onto a positive NAO phase and modifications of the cloud cover and the atmospheric humidity profiles. This work shows the potential improvements of the atmospheric and oceanic mean states and intraseasonal variability that would be brought by a hourly coupling and the use of high resolution ocean general circulation models in the ocean-atmosphere coupled simulations.
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https://tel.archives-ouvertes.fr/tel-00451936
Contributor : Virginie Guemas <>
Submitted on : Monday, February 1, 2010 - 10:48:18 AM
Last modification on : Thursday, August 6, 2020 - 4:32:22 PM
Long-term archiving on: : Thursday, October 18, 2012 - 1:57:46 PM

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  • HAL Id : tel-00451936, version 1

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Virginie Guemas. Rôle de la surface marine sur la variabilité intrasaisonnière estivale de l'atmosphère dans la région Nord Atlantique Europe. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2009. Français. ⟨tel-00451936⟩

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