Earth Rotation Wobble

Chandler wobble, annual oscillation, and length-of-day variations

Polar motion path (meters from mean pole)
Chandler Amplitude (m)0.4 m
Annual Amplitude (m)0.15 m
Chandler Period (days)433 d
Phase Drift0.8 rad
Chandler period:433 days
Beat period:6.2 yr
Current amplitude:0.4 m
ΔΛ (LOD):±1.0 ms
Excitation:Atm + Ocean
The Chandler wobble (S. C. Chandler, 1891) is the free Euler wobble of a non-rigid Earth: the pole traces a ~6–9 m circle with period ~433 days (~14 months). For a rigid body, the period would be 305 days (Euler period); the difference reveals Earth's internal structure. Superposed with the annual wobble (driven by seasonal atmosphere/ocean redistribution), the pole traces a beat pattern with ~6.2 year envelope. The Chandler wobble decays over decades without atmospheric and oceanic excitation — the pumping mechanism was only identified in 2000 (Gross 2000). LOD varies by ±1 ms due to atmosphere–Earth angular momentum exchange.