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Chandler Wobble: Why the Earth Wobbles Like a Toy Top


Planetary Wobbles

What is the Chandler Wobble?

Earth spins on its axis of rotation. But it doesn’t spin perfectly.

Like a toy top, it wobbles when it spins. This displacement is known as the Chandler Wobble.

The wobble is minuscule. It’s just 20 feet in deviation at the North Pole.

It’s also periodic. This means it takes 433 days to fully complete a deviated wobble.

Wobbling from ocean bottom pressure

Over time, we’d expect Earth’s wobbles to even out and disappear. But the activating force that drives Earth’s wobble persists.

The Chandler Wobble has been a mystery for quite some time. This is until R.S. Gross modeled atmospheric and oceanic excitation processes [1].

His research attributes ocean-bottom pressure as the major contributor in exciting the Chandler Wobble. Next, atmospheric winds and oceanic currents are only minor contributors.

While ocean temperature and salinity changes cause two-thirds, he concludes the remaining one-third is caused by atmospheric pressure.

Earth’s rotation and wobble

Chandler Wobbles

Over the years, scientists have put forward several theories for what activates the Chandler Wobble.

For example, theories include variations in global water distribution, interactions between Earth’s inner layers and atmospheric fluctuations.

But R.S. Gross characterizes Earth’s Wobble two-thirds from ocean-bottom pressure and one-third from variations in atmospheric pressure.

He was able to unravel this mystery by analyzing the atmospheric angular momentum data from the International Earth Rotation Service (IERS).


R.S. Gross. “The excitation of the Chandler Wobble” Jet Propulsion Laboratory, California Institute of Technology, Pasadena. Geophysical Research Letters, Vol. 27, No. 15, Pages 2329-2332, August 1, 2000.

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