An Earth-like numerical dynamo model

The mechanism by which the Earth and other planets maintain their magnetic fields against ohmic decay is among the longest standing problems in planetary science. Although it is widely acknowledged that these fields are maintained by dynamo action, the mechanism by which the dynamo operates is in large part not understood. Numerical simulations of the dynamo process in the Earth's core have produced magnetic fields that resemble the Earth's field, but it is unclear whether these models accurately represent the extremely low values of viscosity believed to be appropriate to the core. Here we describe the results of a numerical investigation of the dynamo process that adopts an alternative approach to this problem in which, through the judicious choice of boundary conditions, the effects of viscosity are rendered unimportant. We thereby obtain a solution that at leading order operates in an Earth-like dynamical regime. The morphology and evolution of the magnetic field and the fluid flow at the core–mantle boundary are similar to those of the Earth, and the field within the core is qualitatively similar to that proposed on theoretical grounds.

[1]  Jeremy Bloxham,et al.  Time‐dependent mapping of the magnetic field at the core‐mantle boundary , 1992 .

[2]  T. Russell,et al.  Intercalibration of small-angle X-ray and neutron scattering data , 1988 .

[3]  Dorian A. Canelas,et al.  Solution properties of a CO2-soluble fluoropolymer via small angle neutron scattering , 1996 .

[4]  Paul H. Roberts,et al.  Rotation and Magnetism of Earth's Inner Core , 1996, Science.

[5]  C. Hawker,et al.  Unimolecular micelles and globular amphiphiles: dendritic macromolecules as novel recyclable solubilization agents , 1993 .

[6]  S. I. Braginskii.  An almost axially-symmetrical model of the hydromagnetic dynamo of the earth. I. , 1975 .

[7]  J. Taylor,et al.  The magneto-hydrodynamics of a rotating fluid and the earth’s dynamo problem , 1963, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[8]  C. Jones,et al.  Influence of the Earth's inner core on geomagnetic fluctuations and reversals , 1993, Nature.

[9]  Jean M. J. Fréchet,et al.  One-step synthesis of hyperbranched dendritic polyesters , 1991 .

[10]  G. Glatzmaier,et al.  A three-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle , 1995 .

[11]  J. V. Hest,et al.  Synthesis, characterization, and guest-host properties of inverted unimolecular dendritic micelles , 1996 .

[12]  K. Johnston,et al.  Dispersion Polymerization of Methyl Methacrylate Stabilized with Poly(1,1-dihydroperfluorooctyl acrylate) in Supercritical Carbon Dioxide , 1995 .

[13]  Jeremy Bloxham,et al.  Torsional oscillations and the magnetic field within the Earth's core , 1997, Nature.

[14]  D. Pfund,et al.  FLUID STRUCTURE IN SUPERCRITICAL XENON BY NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY AND SMALL ANGLE X-RAY SCATTERING , 1994 .

[15]  C. Reichardt.  Empirical Parameters of Solvent Polarity as Linear Free‐Energy Relationships , 1979 .

[16]  P. Roberts,et al.  An anelastic evolutionary geodynamo simulation driven by compositional and thermal convection , 1996 .

[17]  D. Canelas,et al.  Dispersion Polymerization of Styrene in Supercritical Carbon Dioxide: Importance of Effective Surfactants , 1996 .

[18]  E. W. Meijer,et al.  Poly(propylene imine) Dendrimers: Large‐Scale Synthesis by Hetereogeneously Catalyzed Hydrogenations , 1993 .

[19]  J. Bloxham.  The steady part of the secular variation of the Earth's magnetic field , 1992 .

[20]  Dorian A. Canelas,et al.  Design of Nonionic Surfactants for Supercritical Carbon Dioxide , 1996, Science.

[21]  James R. Dewald,et al.  A New Class of Polymers: Starburst-Dendritic Macromolecules , 1985 .

[22]  Z. Guan,et al.  Synthesis of Fluoropolymers in Supercritical Carbon Dioxide , 1992, Science.

[23]  D. Jault,et al.  Westward drift, core motions and exchanges of angular momentum between core and mantle , 1988, Nature.

[24]  J. Fréchet,et al.  Functional polymers and dendrimers: reactivity, molecular architecture, and interfacial energy. , 1994, Science.

[25]  Paul H. Roberts,et al.  A three-dimensional self-consistent computer simulation of a geomagnetic field reversal , 1995, Nature.

[26]  D. M. Grove,et al.  Homogeneous catalysts based on silane dendrimers functionalized with arylnickel(II) complexes , 1994, Nature.

[27]  D. Canelas,et al.  Dispersion polymerizations in carbon dioxide using siloxane-based stabilizers , 1996 .

[28]  Edward Crisp Bullard,et al.  Homogeneous dynamos and terrestrial magnetism , 1954, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[29]  A. Cooper,et al.  Polymer synthesis and characterization in liquid / supercritical carbon dioxide , 1996 .

[30]  C. Jones,et al.  A geodynamo model incorporating a finitely conducting inner core , 1993 .

[31]  S. Howdle,et al.  Solubilization in nonionic reverse micelles in carbon dioxide , 1994 .

[32]  J. DeSimone,et al.  Dispersion Polymerizations in Supercritical Carbon Dioxide , 1994, Science.

[33]  M. Capel,et al.  Aggregation of amphiphilic molecules in supercritical carbon dioxide: A small angle X-ray scattering study , 1995 .

[34]  Frank V. Bright,et al.  Water-in-Carbon Dioxide Microemulsions: An Environment for Hydrophiles Including Proteins , 1996, Science.