Atmospheric and Oceanic Excitations to LOD Change on Quasi-biennial Tune Scales

<正>We use wavelet transform to study the time series of the Earth's rotation rate (length-of-day, LOD), the axial components of atmospheric angular momentum (AAM) and oceanic angular momentum (OAM) in the period 1962-2005, and discuss the quasi-biennial oscillations (QBO) of LOD change. The results show that the QBO of LOD change varies remarkably in amplitude and phase. It was weak before 1978, then became much stronger and reached maximum values during the strong El Nino events in around 1983 and 1997. Results from analyzing the axial AAM indicate that the QBO signals in axial AAM are extremely consistent with the QBOs of LOD change. During 1963-2003, the QBO variance in the axial AAM can explain about 99.0% of that of the LOD, in other words, all QBO signals of LOD change are almost excited by the axial AAM, while the weak QBO signals of the axial OAM are quite different from those of the LOD and the axial AAM in both time-dependent characteristics and magnitudes. The combined effects of the axial AAM and OAM can explain about 99.1% of the variance of QBO in LOD change during this period.