Revisiting core contributions to Length-of-day variations.

The length-of-day (LOD) is influenced by various factors, including the periodic deformations of the solid Earth caused by the gravitational forces of the Sun, Moon, and other planets. These well-documented effects, along with secular trends primarily attributed to tidal dissipation and glacial isostatic adjustment (GIA), are removed from the data to focus on other influences. Atmospheric excitations, and oceanic excitations when possible, are also accounted for, as they play a significant role in LOD variations across seasonal, inter-annual, and intra-annual timescales.

On longer timescales (decadal, inter-decadal, and intra-decadal), LOD variations are primarily associated with processes within Earth's core, with potential contributions from external mechanisms. Angular momentum is transferred to the solid Earth primarily through core dynamics, with torsional Alfvén oscillations and large-scale magneto-Coriolis waves identified as key drivers of these variations.

To investigate the origins of LOD fluctuations, we analyze modern and historical observations spanning periods from years to millennia. Employing techniques such as Fast Fourier Transform (FFT), Morlet wavelet analysis, singular spectrum analysis (SSA), and the Lomb-Scargle periodogram (LSP) for uneven data intervals, we extract and verify trends, frequencies, amplitudes, and phases of periodic components. Our comprehensive amplitude-period distribution analysis strongly indicates that Earth's core dynamics are the dominant drivers of LOD variations on timescales exceeding the annual cycle.