This is something of a technical question, and it may not be on topic. But I've managed to thoroughly confuse myself about it and I figured if any Stack could help me it would be this one.

It is known from classical mechanics that a rigid body with a rotational symmetry axis will undergo "torque-free precession". As viewed in a reference frame rotating with the body, the instantaneous rotation axis will appear to precess around the symmetry axis. This precession will proceed clockwise for a prolate body, and counter-clockwise for an oblate body.

In the case of the Earth, this torque-free precession manifests as the Chandler wobble. At least some of the sources I've found online mention that this precession proceeds counter-clockwise in the Earth's frame, which makes sense because the Earth is an oblate body. The period of this wobble is about one year, which also (roughly) matches the prediction from classical mechanics.

I'm talking about this phenomenon in one of my classes soon, and I sought out some data to illustrate it. I found the Earth orientation data from the IERS, and plotted out the long-term data, and it does indeed show the Earth's pole precessing in a circle with a radius of about 200 mas, with a period of about one year. The problem is that the precession in this data set appears to be clockwise, not counter-clockwise as predicted. You can see the plot in a nice 3D Javascript-rendered graph on the IERS website, which I've screenshotted below.

Why is this? Am I misunderstanding what this data set is showing, and this motion isn't the Chandler wobble at all? Is there some subtlety of the coordinate systems in use that I'm missing? Is it something else entirely?

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