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Liquid Metal MHD and the Geodynamo

  • H. K. Moffatt
Part of the Mechanics of Fluids and Transport Processes book series (MFTP, volume 10)

Abstract

The magnetic field of the Earth is generated by dynamo action associated with the upwelling of buoyant material in the liquid outer core. It is argued that this upwelling occurs in the form of mushroom-shaped blobs of material released from the mushy zone at the inner core boundary (ICB), and having a very small density defect δρ/ρ. The rise of buoyant material with velocity w is compensated by the slow rate of growth of the solid inner core. The resulting mass balance, combined with approximate geostrophic force balance in the core leads to estimates
$$\delta \rho /\rho \sim 3 \times {10^{ - 9}},w \sim 2 \times {10^{ - 4}}m/s.$$
Each rising blob drives a Taylor column, and the helicity and α-effect associated with this flow is estimated. A mean-field dynamo driven by this α-effect in conjunction with differential rotation generates a magnetic field whose strength is determined in order of magnitude by the plausible assumption of magnetostrophic equilibrium.

Keywords

Inner Core Mushy Zone Differential Rotation Liquid Core Magnetic Reynolds Number 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Kluwer Academic Publishers 1989

Authors and Affiliations

  • H. K. Moffatt
    • 1
  1. 1.Department of Applied Mathematics and Theoretical PhysicsCambridgeUK

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