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Représentation numérique et mathématique des structures météorologiques cohérentes d'échelle synoptique

Matthieu Plu 1
1 Équipe Cyclones
CNRM-GAME - Groupe d'étude de l'atmosphère météorologique
Abstract : The meteorological synoptic-scale phenomena may be explained by the nonlinear interactions between some finite-amplitude structures and their large-scale environment. This framework of study does not rely on the hardly justifiable hypotheses of the instability theories, but it requires to be able to represent in an objective manner the coherent structures, named like this by analogy with turbulent flows.
The main purpose of this thesis is to build and to assess an algorithm of extraction of the synoptic-scale coherent structures. They are sought only in the field of potential vorticity, which is invertible in the dry atmosphere. The inversion yields the attribution of the other dynamical fields to the structure. The extraction relies on the projection of two-dimensional fields on a set of orthogonal wavelet bases. An optimal basis is associated with every structure. In order to avoid any redundancy between the structures, a technique of orthogonalization has been set. The comparison of the extraction with a non-objective method is made possible by a new definition of the temporal coherence, that relies on the independance of the evolution of the environment.
The extraction has been applied to a large set of synoptic-scale phenomena: a high-frequency upper-level precursor, a jet-streak, and some upper-level fields associated with intense precipitating events in the Mediterranean. These studies help to show the dynamical consistency of the extracted structures, and to identify some possible applications of the algorithm. Its potential use for the short-term ensemble forecast of storms is also tackled.
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Matthieu Plu. Représentation numérique et mathématique des structures météorologiques cohérentes d'échelle synoptique. Océan, Atmosphère. Université Paul Sabatier - Toulouse III, 2008. Français. ⟨tel-00286510⟩

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