SEASONAL OSCILLATIONS IN LENGTH-OF-DAY

Variations of annual and semiannual oscillations in rotation parameter s have been investigated on the basis of length-of-day (LOD) as well a s atmospheric-angular-momemtum (AAM) series. These oscillations were d etermined using band-pass filters. In order to show the character of v ariations of seasonal oscillations, amplitudes, phases and periods wer e computed by a least-squares adjustment with the method of modified h armonic analysis at quarterly intervals. In addition, the seasonal imb alances in LOD and AAM budgets were determined and analysed in a simil ar way. These discrepancies were corrected for tidally excited effects . The non-atmospheric oscillations without the annual tide effect Sa a nd the semiannual tide effect Ssa have variable amplitudes between 0.0 2 and 0.10 msec.