Fig. 4: Schematic depiction of the tilted inner core wobble (ICW).
From: Inner core static tilt inferred from intradecadal oscillation in the Earth’s rotation
The figure axis of the inner core wobbles about its rotation axis tilted to the mantle in a small circular orbit (see blue shaded area). Ωm is the rotation axis of the mantle, Ω′m and Ωic are respectively the rotation axis and dynamic figure axis of the inner core, and θ is the static tilt angle between Ωm and Ω′m. The upper right subgraph shows how to get θ from the mantle-inner core gravitational torque in the mantle’s axial and equatorial directions \(|{{{{{{\boldsymbol{\Gamma }}}}}}}_{z}^{{{{{{\rm{MICG}}}}}}}|\) and \(|{{{{{{\boldsymbol{\Gamma }}}}}}}_{{{{{{\rm{eq}}}}}}}^{{{{{{\rm{MICG}}}}}}}|\) (see also in Methods).
