  The problem of coherent vortex and zonal jet formation in a system of
nonlinear Rossby waves is considered from the point of view of the late time
steady state achieved by free decay of a given initial state. Statistical
equilibrium equations respecting all conservation laws are constructed,
generalizing those derived previously for 2D inviscid Euler flow. Jet-like
solutions are ubiquitous, with large coherent vortices existing only when there
is uniform background flow with the precise velocity to cancel the beta effect.

Statistical Mechanics;Fluid Dynamics