The Earth rotation undergoes changes under the influence of the lunisolar gravitational torque and various geophysical excitations. Whereas the lunisolar forcing can be well modelled as the sum of periodic terms through the Tides Generating Potential (TGP) , the geophysical excitation remains unpredictable, and has to be computed from various sets of geophysical data. In the following page we present links to time series of :
  • Atmospheric Angular Momentum (AAM) excitation functions (routinely derived) and atmospheric torque on the solid Earth
  • Oceanic Angular Momentum (OAM)
  • Hydrological Angular Momentum (HAM) excitation functions
  • Core angular momentum (CAM) associated with core-mantle electromagnetic coupling
These forcings can be compared to the ones observed in polar motion (PM) and lenght of day (LOD). Here below we provide also the "observed excitation" for periods > 5-10 d, as computed from EOP combined series "C04" for PM and LOD.

Observed excitation

comparison with geophysical excitation

IERS Global Geophysical Fluid Center
Atmospheric excitation

Oceanic excitation
Hydrological excitation
Core-mantle coupling