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Dynamics of stratified regions in Saturn

Kirk, Joshua Robert (2018) Dynamics of stratified regions in Saturn. PhD thesis, University of Leeds.

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Abstract

Saturn has a rather peculiar magnetic field in that it is highly spin axisymmetric. Evidence for the decay time of a magnetic field on the scale of Saturn would suggest that a dynamo operates deep within its interior. As a consequence, the observed field would be in violation of Cowling’s theorem. It is believed that a stably stratified layer under the influence of a thermal shear is the reason for the observed axisymmetric field. This stable layer is believed to be formed from helium sedimentation deep within Saturn, with the thermal shear driven by pole-equator temperature differences. The combined effects of shearing and the stable layer attenuate the non-axisymmetric field components leaving only the axisymmetric field at the surface. Motivated by the influence of this stable stratification, we follow on from initial work by Stevenson (1982b) by first considering the linear problem with variable conductivity and looking at the consequences of increasing the parameter that controls the strength of the thermal wind as mentioned in his paper. In subsequent chapters the analysis concentrates on the nonlinear contributions by including the momentum equation into our calculations. We present asymptotic analysis of such a system and show that the geostrophic flow, found by satisfying Taylor’s constraint, is singular for an inviscid interior solution in the limit of small Rm, where Rm, the magnetic Reynolds number, controls the strength of the shearing effect within the layer. Numerical treatment of the system of equations for a viscous system are also considered. The results of exploring the parameter space for Rm and Ha, the Hartmann number, lead to further asymptotic analysis in which viscosity is considered. A boundary layer solution is found, which is validated by the numerical solution. The latter part of the thesis looks at the numerical solution with the inclusion of a horizontal field, the motivation for which will become apparent in the analysis of the inviscid regime.

Item Type: Thesis (PhD)
Keywords: Saturn
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds)
The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Mathematics (Leeds)
The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Mathematics (Leeds) > Applied Mathematics (Leeds)
Identification Number/EthosID: uk.bl.ethos.759797
Depositing User: Mr Joshua Robert Kirk
Date Deposited: 27 Nov 2018 12:53
Last Modified: 18 Feb 2020 12:32
URI: http://etheses.whiterose.ac.uk/id/eprint/22193

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