Asymptotic Hamiltonian reduction for the dynamics of a particle on a surface

We consider the motion of a particle on a surface which is a small perturbation of the standard sphere. One may qualitatively describe the motion by means of a precessing great circle of the sphere. The observation is employed to derive a subsidiary Hamiltonian system that has the form of equations for the top with a 4-th order Hamiltonian, and provides the detailed asymptotic description of the particle's motion in terms of graphs on the standard sphere.