Analysis
It consists of two quasi-periodic components and a gradual drift, mostly in the direction of the 80th meridian west, of the Earth's instantaneous rotational axis or North pole, from a conventionally defined reference axis, the CIO (Conventional International Origin), being the pole's average location over the year 1900.
The two periodic parts are a more or less circular motion called Chandler wobble with a period of about 435 days, and a yearly circular motion. There is also a longer term variation which is less well understood. These motions are illustrated on the Earth Orientation Center of the International Earth Rotation and Reference Systems Service (mas = milliarcseconds corresponds to about 3 cm):
- polar motion from 2005 until the last week
- x coordinate from 1962 until the last week
- y coordinate from 1962 until the last week
The mean displacement far exceeds the magnitude of the wobbles. This can lead to errors in software for Earth observing spacecraft, since analysts may read off a 5 meter circular motion and ignore it, while a 20 meter offset exists, fouling the accuracy of the calculated latitude and longitude. The latter are determined based on the International Terrestrial Reference System, which follows the polar motion.
Read more about this topic: Polar Motion
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