# Paris Observatory Geodetic VLBI Center

## Free core nutation from IERS data

This page displays the information relevant to the empirical modeling of the free nutation of the Earth's figure axis associated with the free rotational mode of the fluid core inside the viscoelastic mantle (free core nutation or FCN). The empirical models are obtained by least-square fit to various series submitted to or computed by the IERS Earth Orientation Center. The models are updated regularly, typically every week as series are updated by the analysis centers. A notice provides information about the model. A Fortran subroutine is also provided to obtain FCN values at any epoch from a given empirical model. For each series, we make available a table of yearly amplitudes and a time series of the FCN values at the epochs of the data. Series ivq and ivr refer to the IVS quarterly and rapid combinations, respectively. Click on the plots to enlarge.

### Amplitude and phase comparison

### Individual data and models