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Abstract

Compared to the Chandler and annual wobbles, the higher-frequency components of polar motion (PM) have substantially smaller amplitudes. Therefore, their study had to wait until higher-quality time series with high temporal resolution, as measured by space geodetic techniques, became available. Based on the combined Earth orientation series SPACE99 computed by the Jet Propulsion Laboratory (JPL) from 1976 to 2000 at daily intervals, we have separated the periodic PM terms by band-pass filtering and found that the persistence of oscillations becomes less with increasing frequency (H¨opfner 2001a, b). In order to quantify and better describe the parameter variability of these PM components over time, particularly of eight oscillations with periods ranging between about 650 and 45 days, we computed the radii, direction angles and period lengths from the periodic terms filtered out from the time series. The results clearly show the characteristics and time evolution of the periodic PM components that are important for geophysical interpretations.