Variation in the Earth's figure axis owing to geophysical cause, minutely determined from polar motion

TL;DR

This paper analyzes Earth's figure axis variations caused by geophysical factors using polar motion data, deriving equations to determine the figure pole's motion and revealing both rapid short-term and stable long-term variations.

Contribution

It introduces equations relating the figure and rotational axes and demonstrates the ability to accurately determine the figure pole's position from polar motion data.

Findings

Rapid, complex short-term motion of the figure pole.

Stable annual and semi-annual variations in long-term averages.

Determination accuracy is sufficient to detect short-duration variations.

Abstract

The variation in the figure axis in the Earth owing to the geophysical causes directly reflects the physical state of the Earth and therefore, it is important for understanding the Earth. Of the variations in the figure axis arising from different causes, the variation owing to the Earth's geophysical causes is determined from polar motion data. Equations that give the relation between the figure axis and rotational axis are derived and the motion of the figure pole with respect to the Earth's surface or the figure axis in the Earth is determined by using these equations. Estimation of error suggests that the accuracy of the determination for the position of the figure pole at each moment is sufficiently good and that even a variation that occurs during a short duration of time, such as one or two days, is significant. The determined position of the figure pole exhibits a rapid and complicated motion in a short duration. On the other hand, a long-range average of the pole shows stable annual and semi-annual variations, but it is quite independent of the Chandler wobble.