2000b) The excitation of the Chandler wobble

Abstract. Any irregularly shaped solid body rotating about some axis that is not aligned with its figure axis will wobble as it rotates. For the Earth, this Eulerian free wobble is known as the Chandler wobble in honor of S. C. Chandler who first observed it in 189 1 1. From the observations of the Chandler wobble taken since its discovery, its period has been estimated to be 433.0 f 1.1 (lo) days and its e-folding amplitude decay time has been estimated to be 68 years (with lo bounds of 28 and 298 years)2. Because a damping time of 68 years is short on a geological time-scale, the amplitude of the Chandler wobble should quickly dampen to zero unless ome mechanism or combination of mechanisms are exciting it. Since its discovery, many mechanisms have been evaluated, without success, to determine whether or not they could be the excitation mechanism(s) of the Chandler wobble including atmospheric processes3-7, continental water storageg-1 l, core-mantle interactions12-16, and earthquakes17.18. Here, evidence is presented that the Chandler wobble is excited by a combination of atmospheric and oceanic processes, with ocean-bottom pressure fluctuations being the dominant excitation mechanism. Measurements of the Earth’s changing rotation are currently made by the space-geodetic techniques of satellite and lunar laser ranging, very long baseline interferometry, and globa