SEMINAIRE MERCREDI 22 JUIN 2005 14 heures Salle Séminaire 5 Centre de Physique Théorique Marseille-Luminy Stefanella Boatto Institut Henri Poincaré, Paris & Dept. of Mathematics & Statistics, McMaster University, Canada Titre: Periodic solutions of Euler equation on a sphere Résumé: Classes of steady and periodic solutions are investigated for the incompressible Euler equation. Of particular interest is the stability of "discrete solutions" of the type of point-vortices on the plane and on the sphere,on domains without boundaries and outside a cylinder. The study makes use of an infinite dimensional Hamiltonian formulation of the vorticity equation when the rotation of a planet is taken into account (see T.G. Shepherd, Hamiltonian Dynamics, Encyclopedia of Atmospheric Sciences, Academic Press, pp 929-938, 2003)