On the influence of a translating inner core in models of outer core convection

Davies, C.J., Silva, L. and Mound, J. (2013) On the influence of a translating inner core in models of outer core convection. Physics of the Earth and Planetary Interiors, 214, pp. 104-114. (doi: 10.1016/j.pepi.2012.10.001)

Abstract

It has recently been proposed that the hemispheric seismic structure of the inner core can be explained by a self-sustained rigid-body translation of the inner core material, resulting in melting of the solid at the leading face and a compensating crystallisation at the trailing face. This process induces a hemispherical variation in the release of light elements and latent heat at the inner-core boundary, the two main sources of thermochemical buoyancy thought to drive convection in the outer core. However, the effect of a translating inner core on outer core convection is unknown. In this paper we model convection in the outer core using a nonmagnetic Boussinesq fluid in a rotating spherical shell driven by purely thermal buoyancy, incorporating the effect of a translating inner core by a time-independent spherical harmonic degree and order 1 (Y11 ) pattern of heat-flux imposed at the inner boundary. The analysis considers Rayleigh numbers up to 10 times the critical value for onset of nonmagnetic convection, a parameter regime where the effects of the inhomogeneous boundary condition are expected to be most pronounced, and focuses on varying q*, the amplitude of the imposed boundary anomalies. Increasing q∗ leads to flow patterns dominated by azimuthal jets that span large regions of the shell where radial motion is significantly inhibited. Vigorous convection becomes increasingly confined to isolated regions as q∗ increases; these regions do not drift and always occur in the hemisphere subjected to a boundary heat-flux that is higher than the average. Effects of the inner boundary anomalies are visible at the outer boundary in all models that were attempted. At low q ∗ the surface expression of inner boundary effects is an amplitude difference between the two hemispheres. As q∗ increases the spiralling azimuthal jets driven from the inner boundary are clearly visible at the outer boundary. Finally, our results suggest that, when the system is heated from below, a Y11 heat-flux pattern imposed on the inner boundary has a greater overall influence on the spatio-temporal behaviour of the flow than the same pattern imposed at the outer boundary.

• Item Type: Articles (Letter)
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Silva, Dr Luis
• Authors: Davies, C.J., Silva, L., and Mound, J.
• Subjects: Q Science > QC Physics
• College/School: College of Science and Engineering > School of Mathematics and Statistics > Mathematics
• Journal Name: Physics of the Earth and Planetary Interiors
• Journal Abbr.: Phys. Earth Planet. Int.
• Publisher: Elsevier
• ISSN: 0031-9201
• ISSN (Online): 1872-7395