Systems of Hydrodynamic Type that Approximate Two-Dimensional Ideal Fluid Equations

Statistical properties of different finite-dimensional approximations of two-dimensional ideal fluid equations are studied. A special class of approximations introduced by A.M. Obukhov (systems of hydrodynamic type) is considered. Vorticity distributions over area and quasi-equilibrium coherent structures are studied. These coherent structures are compared to structures occurring in a viscous fluid with random forcing.