Geometry of the problem; namely, the beta-plane approximation in which the equations are written in Cartesian coordinates in a plane tangent to the sphere at a given latitude, and the so-called beta-effect results from the meridional gradient of the local vertical component of the Coriolis parameter. A constant background magnetic field is considered at the reference latitude pointing in the x (east-west) direction, resulting in Rossby waves that will have both velocity and magnetic field perturbations that propagate in the x direction.