Hilbert-Huang Transform Analysis of Intradecadal Variations in the Length of Earth's Day

Intradecadal periods in the length of Earth's day (∆LOD) reveal angular momentum exchanges as a result of processes in the Earth's core. The properties of two previously identified intradecadal oscillations in the ∆LOD signal with periods of approximately 6 and 8.5 years, respectively, are investigated from 1962 to 2025, using the Hilbert-Huang transform method. Initially, angular momentum contributions from zonal tides and the Earth's atmosphere are removed, before the application of Butterworth bandpass filters to isolate the oscillations. The two intradecadal oscillations are found to have periods of 5.8 ± 0.8 years and 9.1 ± 1.6 years, respectively. The six-year oscillation shows a decaying trend from 2010 onwards, associated with a shortening in the period of oscillation. The eight-year oscillation breaks down between 1995 and 2000, which may be linked with geomagnetic jerk activity.