An Analysis of the Pole Offset Series in EOP(GSFC) 96 R 01

Observations of the IAU 1980 nutation daily of fsets in longi tude (W△j) and obliquity (W△X) from Mark Ⅲ VLBI delay data between Aug. 1979 and Jan. 1996 are analyzed for the corrections to coefficients of the largest IAU 1980 nutation terms and for the detection of the free core nutation. The computation is designed for the following general data processing algorithm with skills adopted for a possible best use of the whole data span and a reduction of the edge effect of data series on solutions. Further analy sis of the post-fit residuals suggests that the free core nutation is statistically signi ficant and its parameters may be characterized by time-variation, especially for the amplitude, which was decreasing from 1986 to 1995 for bo th W△j and W△X. Geophysical explanation is still leaving unknown.