EGU22-7481, updated on 03 Dec 2023
EGU General Assembly 2022
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Effects of topographic coupling at core-mantle boundary in rotation and orientation changes of the Earth.

Véronique Dehant1,2, Jeremy Rekier1, Mihaela Puica3, Marta Folgueira Lopez4, Antony Trihn5, and Tim Van Hoolst1
Véronique Dehant et al.
  • 1Royal Observatory of Belgium, Brussels, Belgium
  • 2Université catholique de Louvain, Belgium
  • 3University of Oslo, Faculty of Mathematics and Natural Sciences, Norway
  • 4Universidad Complutense de Madrid, Spain
  • 5University of Arizona, Tucson, USA

We study coupling mechanisms at the topographic core-mantle boundary (CMB) of the Earth in the frame of nutations and Length-of-Day (LOD) variations. The CMB topography is usually considered to have a smooth spherical or elliptical shape, however, in reality it is bumpy and there are mountains and valleys representing local height differences of the order of a kilometer. The existence of a topography induces inertial waves that need to be considered in the flow of the core. This is in addition to the Poincaré fluid motion when the nutations are computed and in addition to a relative rotation of the fluid opposite and of the same amplitude as that of the mantle for LOD variations. The additional pressure and the topographic torque depend on the shape of the CMB and can be related to the spherical harmonic coefficients of the CMB topography. We follow the philosophy of the computation of Wu and Wahr [Geophys. J. Int., 128(1), 18-42, 1997] and determine the coefficients of the velocity field in the core at the CMB in terms of the topography coefficients. We used an analytical approach instead of a numerical one. We confirm that some topography coefficients may enhance length-of-day variations and nutations at selected frequencies, and show that these increased rotation variations and nutations are due to resonance effects with inertial waves in the incremental core flow.

How to cite: Dehant, V., Rekier, J., Puica, M., Folgueira Lopez, M., Trihn, A., and Van Hoolst, T.: Effects of topographic coupling at core-mantle boundary in rotation and orientation changes of the Earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7481,, 2022.