自由地核章动的时变特性

对VLBI观测确定的IAU1980章动模型的天极偏移序列进行分析，结果显示自由地核章动在1990年以前的幅值比其后为强，其时变强度比周年受迫章动的为大．另外，小波变换的时频谱分析结果显示在天极偏移序列中存在一幅值约0．1毫角秒的准两年周期信号．仅从目前的数据分析结果尚不足以确定此信号与顺向自由地核章动之间的关系，进一步的观测检，验和深入的内核动力学研究是非常必要的．

THE TEMPORAL VARIATIONS OF THE FREE CORE NUTATION

In this paper the pole daily offsets of the IAU 1980 Nutation Theory from VLBI observations are analyzed with the multistage filter and wavelet transform methods.The results indicate that in the data span the magnitude of the free core nutation before 1990 is larger than aftenwards. The temporal variations in the free core nutation are more intense than those in the forced annual nutation term. The time-frequency spectrum of wavelet transform of the pole offset observations also suggests the existence of a discernible signal in the quasi-bieeial frequency and with a magnitude of about 0.1 mas. With our results based only on the results of data analysis in this paper it is too early to affirm the relation between the signal in quasi-biennial frequency and the prograde free core nutation associated with the solid inner core dynamics. Further analyses of observations and deep studies of the inner core dynamics will be essential to solve this problem.