We study the two-dimensional surface quasi-geostrophic equations and the three-dimensional Hall-magnetohydrodynamics system forced by degenerate noise. In comparison with a vorticity formulation of the Navier–Stokes equations, the non-linear term of the surface quasi-geostrophic equations is more singular by one derivative. In comparison with the magnetohydrodynamics system, the Hall term of the Hall-magnetohydrodynamics system is also more singular by one derivative. We prove the existence and uniqueness of an invariant measure for the Galerkin approximations of the surface quasi-geostrophic equations and the Hall-magnetohydrodynamics system, both forced by degenerate noise which consists of only a few modes.
- Hall-magnetohydrodynamics system
- Harris’ condition; Hörmander’s condition
- Surface quasi-geostrophic equations