Influence of elastic deformations on the inner core wobble

Abstract

SUMMARY The Earth’s longest free mode of nutation, the inner core wobble (ICW), consists of a prograde precession of the tilted figure of the inner core with respect to a fixed mantle. The dynamics of the ICW is controlled by coupling at the inner-core boundary (ICB) and by the torque exerted by the rest of the Earth on a tilted inner core. This mode has not yet been observed either directly or indirectly, though theoretical estimates suggest its period should be 2410 solar days or 6.6 yr. However, these estimates were based on models that did not properly take into account elastic deformations associated with a tilted inner core. In this work, we incorporate these elastic deformations in a model of free nutations that rests on an angular momentum formalism. We find that based on an elastic, oceanless and dissipationless earth model corresponding to PREM, elastic deformations within the inner core contribute to a lengthening of the period of the ICW from 2410 to 2715 solar days. The internal forcing caused by the misalignment between surfaces of constant density and centrifugal potential is the most important contribution to elastic deformations.