A detailed analysis of a dynamo mechanism in a rapidly rotating spherical shell

F. Takahashi, H. Shimizu

Research output: Contribution to journalArticle

22 Citations (Scopus)

Abstract

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell are investigated using a numerical dynamo model with an Ekman number of 10 -5. A strong dipolar solution with a magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, the convection structure consists of a few large-scale retrograde flows in the azimuthal direction and localized thin sheet-like plumes. A detailed term-by-term analysis of the magnetic field amplification processes shows that the magnetic field is amplified through stretching of magnetic lines, which occurs typically through four types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, the prograde azimuthal flow near the rim of the tangent cylinder, and the cylindrical-radially alternating flows of the plume cluster. The current loop structure emerges as a result of stretching the magnetic lines along the magnetic field by the flow acceleration. The most remarkable effects of the generated magnetic field on the flow come from the strong azimuthal (toroidal) magnetic field. Similarities of the present model in the convection and magnetic field structures to previous studies at larger and even smaller Ekman numbers suggest universality of the dynamo mechanism in rotating spherical dynamos.

Original languageEnglish
Pages (from-to)228-250
Number of pages23
JournalJournal of Fluid Mechanics
Volume701
DOIs
Publication statusPublished - Jun 25 2012

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spherical shells
Magnetic fields
magnetic fields
plumes
Stretching
DC generators
convection
rotating generators
conducting fluids
Kinetic energy
rims
Amplification
tangents
Numerical models
free convection
inertia
Viscosity
kinetic energy
viscosity
Fluids

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

Cite this

A detailed analysis of a dynamo mechanism in a rapidly rotating spherical shell. / Takahashi, F.; Shimizu, H.

In: Journal of Fluid Mechanics, Vol. 701, 25.06.2012, p. 228-250.

Research output: Contribution to journalArticle

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