On a non-periodic modified Euler equation: existence and quasi-invariant measures

We consider a modified Euler equation on ${\mathbb{R}}^2$. We prove existence of weak global solutions for bounded (and fast decreasing at infinity) initial conditions and construct Gibbs-type measures on function spaces which are quasi-invariant for the Euler flow. Almost everywhere with respect to such measures (and, in particular, for less regular initial conditions), the flow is shown to be also globally defined.