Global simulations of atmosphere, ocean, and land dynamics are used to create effective angular momentum (EAM) functions that can be used to predict changes in EOP.
[3][4] LOD is changing due to gravitational effects from external bodies and geophysical processes occurring in different Earth layers.
The Celestial Ephemeris Pole is calculated from observation data, and is averaged, so it differs from the instantaneous rotation axis by quasi-diurnal terms, which are as small as under 0.01" (see [6]).
The observed differences with respect to the conventional celestial pole position defined by the models are monitored and reported by the IERS.
Some studies indicate that substantial FCN (Free Core Nutation) amplitude and phase disturbances occurred at the epochs close to the revealed GMJ (Geomagnetic Jerk) events.