Partition the core–mantle coupling mechanisms underlying multidecadal LOD variability

Determine how the core-related contribution to multidecadal length-of-day variability is partitioned among electromagnetic, gravitational, topographic, and viscous coupling mechanisms at the core–mantle boundary, because the available observations do not currently support a first-principles attribution.

Background

The paper identifies a near-70-year component in residual length of day (LOD) and a corresponding component in core-angular-momentum-derived equivalent LOD. This correspondence supports a core-related contribution to low-frequency Earth-rotation variability, but it does not establish which physical exchange process at the core–mantle boundary generates the observed signal.

The candidate mechanisms discussed in the paper are electromagnetic, topographic, gravitational, and viscous coupling. Resolving their relative contributions would require observations and physical modeling capable of distinguishing the associated torques rather than merely measuring the aggregate multidecadal LOD response.