Magnetoconvection in the Earth's Core and Flux Expulsion Into the Mantle

Drew, Stephen John (1992) Magnetoconvection in the Earth's Core and Flux Expulsion Into the Mantle. PhD thesis, University of Glasgow.

Abstract

In this thesis we consider a number of problems aimed towards gaining a better understanding of the processes deep in the Earth's core which act to maintain the Ecirth's magnetic field against ohmic decay. Firstly, as a model for the Earth's core, we consider a rapidly rotating electrically conducting fluid sphere with a solid concentric inner core. We impose an azimuthal magnetic field, an azimuthal shear flow and a temperature distribution appropriate to a uniform distribution of heat sources through the core, and investigate numerically the linear stability of this basic state. We consider the effect of inner core radius, magnetic field strength and differential rotation on thermal convection, comparing our results with the work of Fearn and Proctor (1983a) who considered a similar model without an inner core. Later we alter our temperature distribution, attempting to model thermally the effects of compositional convection, the process believed to be the primary power source for the geodynamo. Continuing with the same model, we next study the effect of introducing a stably stratified layer adjacent to the core-mantle boundary. We consider a wide range of magnetic field strengths, and compare our results with work done previously in simpler geometries. Finally, we look at a 2D numerical model of the expulsion of magnetic field from the Earth's core into a conducting mantle, driven by a prescribed upwelling fluid motion. We consider a variety of types of conductivity profile for the mantle and compare with the fully insulating mantle solution as studied by Bloxham (1986). Motivated by the recent work on lower mantle conductivity, we look at a conductivity profile with large lateral heterogeneity in conductivity. All our calculations were performed on the University of Glasgow's IBM 3090-150E/VF mainframe. All om- graphs and contour plots were produced with the aid of the UNIRAS graphics package. The results included in the following chapters can also be found in Drew 1991;1992a,b.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: D R Fearn
• Keywords: Applied mathematics, Geophysics
• Date of Award: 1992
• Depositing User: Enlighten Team
• Unique ID: glathesis:1992-76414
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 14:32
• Last Modified: 19 Nov 2019 14:32
• URI: https://theses.gla.ac.uk/id/eprint/76414