Motions of the Earth's pole as a dynamical three-frequency system

The oscillations of the Earth's pole are considered as a dynamical system i n which the clearly pronounced Chandler period is incommensurate with the e xternally excited annual period. Beats at combined frequencies should be ob served in such systems. The motion of the pole observed over the last centu ry reveal even more complicated behavior. Modeling this behavior requires a t least a three-frequency system, with an additional oscillation period (in ternal or external) that is incommensurate with the two periods mentioned a bove. The desired system is obtained by mapping the first return of the pha se trajectory to a Poincare section, determined from the approximate times of coincidence between the amplitude maxims of the annual and Chandler osci llations of the pole.