Excitation of the Earth's Nutations by the Atmosphere

Precession and nutations are mainly generated by the luni-solar attraction, with additional motions resulting from atmospheric and oceanic forcing associated with diurnal variations in the angular momentum expressed in an Earth-fixed reference system. Observed precession and nutations are derived from the analysis of VLBI data with respect to extragalactic objects which directions are assumed to be fixed in space. After evaluating the possible contamination of VLBI-derived nutation amplitudes by apparent motions of the extragalactic radiosources, we estimate the excitation of Earth's free or forced nutations in the period range 300-1500 days. The correlation in time of VLBI-derived nutations amplitudes with the dominant frequencies in the atmospheric excitations over the last two decades is investigated.