The instantaneous rotation axis drifts across Earth's surface. x_pole points toward the Greenwich meridian, y_pole toward 90°W. Plotting one against the other traces a rosette: the ~435-day Chandler wobble beats against the 12-month annual wobble, so the radius swells and shrinks over a ~6.4-year envelope. Units are arcseconds (1″ ≈ 31 m at the pole).
The difference between Earth-rotation time (UT1) and atomic time (UTC). Its slope is length-of-day excess — the planet speeding up or slowing down by fractions of a millisecond per day.
Winds and surface pressure continuously shove the solid Earth. The effective angular momentum functions χ₁, χ₂, χ₃ quantify that forcing: χ₁/χ₂ drive polar motion, χ₃ drives length-of-day. Mass terms come from pressure loading; motion terms from winds. They are dimensionless and lead the observed pole/LOD response.
Solid lines up to today are the IERS Rapid Service solution from VLBI/GNSS/SLR. The dashed tail is the prediction extrapolated forward — useful but uncertain, widening with lead time. The most recent three years are highlighted to separate current behaviour from the longer baseline.
IERS Bulletin A (daily): datacenter.iers.org/data/csv/bulletina.longtime.csv ·
datacenter.iers.org/data/latestVersion/bulletinA.txt
ESMGFZ AAM (3-hourly): datacenter.iers.org/data/json/ESMGFZ_AAM_v1.0_03h_YYYY.asc.json