The Lie-Poisson Structure of the Euler Equations of an Ideal Fluid

This paper provides a precise sense in which the time t map for the Euler equations of an ideal fluid in a region in Rn (or a smooth compact n-manifold with boundary) is a Poisson map relative to the Lie-Poisson bracket associated with the group of volume preserving diffeomorphism group. This is interesting and nontrivial because in Eulerian representation, the time t maps need not be C from the Sobolev class Hs to itself (where s > (n/2) + 1). The idea of how this difficulty is overcome is to exploit the fact that one does have smoothness in the Lagrangian representation and then carefully perform a Lie-Poisson reduction procedure.