The nutations are daily variations in the Earth's rotation caused by
the torques that the Moon, the Sun and, to a lesser extent, other
planets exert on the equatorial bulge (Figure 1). In this motion, the mantle,
fluid core and inner core are in slight differential rotation. This
is both because they would, in isolation, react differently to the
imposed torque, and also because the forced nutations excite free
rotational modes which involve differential rotation. The overall
nutational response of the Earth depends then on the coupling between
its internal regions. The forcing responsible for the nutation is
known very precisely, and the response of the Earth is also observed
with great precision. Physical models of the internal coupling must
be capable of reproducing the observed nutations when subjected to the
known external torques. Nutations thus provide an opportunity to gain
knowledge on physics taking place deep inside our planet and
inaccessible by direct observations. This includes for example
electromagnetic coupling at the core-mantle and inner core boundaries
(Figure 2). Many of my publications on nutations were done in collaboration with a former postoctoral fellow, Laurence Koot.
Figure 1: Left: Variations in space of the Earth's rotation vector in space as a result of torques from the Sun, Moon and other planets. Right: Actual data.
Figure 2: Electromagnetic coupling between the fluid core and solid inner core (left) and between the fluid core and mantle (right). Differential motion at boundaries deform magnetic field lines which results in a torque.
Some of my papers on this topic
Koot, L. and Dumberry, M., 2013, The role of the magnetic field morphology on the electromagnetic coupling for nutations, Geophys. J. Int., 195, 200-210.
Dumberry, M. and Koot, L., 2012, A global model of electromagnetic coupling for Earth nutations, Geophys. J. Int., 191, 530-544.
Koot, L. and Dumberry, M., 2011, Viscosity of the Earth's inner core: Constraints from nutation observations, Earth Planet. Sci. Lett., 308, 343-349.
Koot, L., Dumberry, M., Rivoldini, A., de Viron, O and Dehant, V., 2010, Constraints on the coupling at the core-mantle and inner core boundaries inferred from nutation observations, Geophys. J. Int., 182, 1279-1294.
Dumberry, M., 2009, Influence of elastic deformations on the inner core wobble, Geophys. J. Int., 178, 57-64.