The transition from liquid metal to silicate rock in the cores of the terrestrial planets is likely to be accompanied by a gradient in the composition of the outer core liquid. The electrical conductivity of a volatile-enriched liquid alloy can be substantially lower than a light-element-depleted fluid found close to the inner core boundary. In this paper, we investigate the effect of radially variable electrical conductivity on planetary dynamo action using an electrical conductivity that decreases exponentially as a function of radius. We find that numerical solutions with continuous, radially outward decreasing electrical conductivity profiles result in strongly modified flow and magnetic field dynamics, compared to solutions with homogeneous electrical conductivity. The force balances at the top of the simulated fluid determine the overall character of the flow. The relationship between Coriolis, and Lorentz forces near the outer core boundary controls the flow and magnetic field intensity and morphology of the system. Our results imply that a low conductivity layer near the top of Mercury's liquid outer core is consistent with its weak magnetic field. (C) 2010 Elsevier B.V. All rights reserved.
机构:
Univ Leeds, Dept Appl Math, Leeds LS2 9JT, W Yorkshire, England
Max Planck Inst Solar Syst Res, Justus von Liebig Weg 3, D-37077 Gottingen, GermanyUniv Leeds, Dept Appl Math, Leeds LS2 9JT, W Yorkshire, England
Dietrich, W.
Jones, C. A.
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Univ Leeds, Dept Appl Math, Leeds LS2 9JT, W Yorkshire, EnglandUniv Leeds, Dept Appl Math, Leeds LS2 9JT, W Yorkshire, England
机构:
Univ Hawaii Manoa, Sch Ocean & Earth Sci & Technol, Hawaii Inst Geophys & Planetol, Honolulu, HI 96822 USA
Univ Hawaii Manoa, Water Resources Res Ctr, Honolulu, HI 96822 USAUniv Grenoble Alpes, CNRS, IRD, IFSTTAR,ISTerre, Grenoble, France