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Regular version of the site

Book chapter

Multidecadal and 6-year variations of LOD

P. 1-17.
Zotov L., Bizouard C., Sidorenkov N., Ustinov A., Ershova T.

The subject of our study is 6-, 20- and 60-year oscillations in the length of day (LOD). Spectral and wavelet analyses of LOD time series have been performed, multidecadal harmonics have been adjusted and simple prediction has been made. Input from the variations of the angular momentum of the ocean and the atmosphere into LOD changes at 6-, 20- and 60-year periods has been analysed. We found out that the oceanic forcing (OAM) of LOD at 20- and 60-year scales is less than 20 microseconds, and 6-year oscillation after atmospheric effects subtraction becomes quite stable with the amplitude of around 0.2 milliseconds. To perform filtering, we used Panteleev's band-pass filter. Since multidecadal oscillations with the amplitude up to 3 milliseconds remain unexplained, we compared them with temperature and sea level anomalies, Chandler wobble and its excitation envelope, and with the Earth's magnetic dipole strength anomaly, a number of processes contain multidecadal variations, the signature of which is quite  similar to LOD changes.