New determination of period and quality factor of Chandler wobble, considering geophysical excitations

Abstract

Polar motion consists of both free (Chandler wobble, with approximately 14-month period) and forced components. The latter are caused by different excitations of geophysical origin. Very long-periodic (or secular) part is most probably due to post-glacial rebound, shorter periodic part (with dominant annual period) are caused mainly by motions of the atmosphere and oceans. Recently it was also proposed that impulse-like excitations due to geomagnetic jerks might be responsible for rapid changes of the amplitude and phase of Chandler wobble. In order to precisely determine the parameters of the free part, it is necessary to consider all these influences. We use the IERS combined solution C04 together with ERA atmospheric/oceanic excitations in the interval 1974.0–2014.0, and also additional excitations due to nine geomagnetic jerks, registered during this interval, to determine the period and quality factor of Chandler wobble, free from these geophysical effects.We obtained solutions for three different time intervals: 1974.0–1994.0, 1994.0–2014.0, and 1974.0–2014.0. The estimated values of Q-factor are much smaller if GMJ excitations are used in addition to atmospheric and oceanic ones, and they are determined with higher accuracy. Our preferred values, valid for the whole interval 1974.0–2014.0, are P=432.86±0.04 days and Q=35.0±0.3.