scholarly journals Spectra and Growth Rates of Fluctuating Magnetic Fields in the Kinematic Dynamo Theory with Large Magnetic Prandtl Numbers

2002 ◽  
Vol 567 (2) ◽  
pp. 828-852 ◽  
Author(s):  
Alexander A. Schekochihin ◽  
Stanislav A. Boldyrev ◽  
Russell M. Kulsrud
Keyword(s):  
Magnetic Fields ◽  
Growth Rates ◽  
Dynamo Theory ◽  
Kinematic Dynamo ◽  
Prandtl Numbers

scholarly journals Structure of small-scale magnetic fields in the kinematic dynamo theory

2001 ◽  
Vol 65 (1) ◽  
Author(s):  
Alexander Schekochihin ◽  
Steven Cowley ◽  
Jason Maron ◽  
Leonid Malyshkin
Keyword(s):  
Magnetic Fields ◽  
Small Scale ◽  
Dynamo Theory ◽  
Kinematic Dynamo

scholarly journals The Small-Scale Photospheric Magnetic Field as an Indicator of the Dynamo

1993 ◽  
Vol 141 ◽  
pp. 143-146
Author(s):  
K. Petrovay ◽  
G. Szakály
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Observational Data ◽  
Convective Zone ◽  
Small Scale ◽  
Dynamo Theory ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Surface Fields

AbstractThe presently widely accepted view that the solar dynamo operates near the base of the convective zone makes it difficult to relate the magnetic fields observed in the solar atmosphere to the fields in the dynamo layer. The large amount of observational data concerning photospheric magnetic fields could in principle be used to impose constraints on dynamo theory, but in order to infer these constraints the above mentioned “missing link” between the dynamo and surface fields should be found. This paper proposes such a link by modeling the passive vertical transport of thin magnetic flux tubes through the convective zone.

scholarly journals Turbulence and magnetic fields in molecular clouds

1991 ◽  
Vol 147 ◽  
pp. 83-92
Author(s):  
R. N. Henriksen
Keyword(s):  
Magnetic Fields ◽  
Wavelet Analysis ◽  
Molecular Clouds ◽  
Fractal Structure ◽  
Compressible Turbulence ◽  
Dynamo Theory ◽  
First Results ◽  
Self Similar

in this paper I first review some of the simple structural concepts associated with compressible turbulence. In particular the hierarchical or self-similar fractal structure to be expected is formulated in a manner readily compared to the observations, and to previous work. In the next section I present the first results of a wavelet analysis on molecular clouds, which seem to comfirm the hierarchical scaling. I conclude with an extention of the theory to include magnetic fields. This latter theory represents an alternative to the more conventional dynamo theory.

Towards a realistic fast dynamo: models based on cat maps and pseudo-Anosov maps

1993 ◽  
Vol 443 (1919) ◽  
pp. 585-606 ◽  
Keyword(s):  
Magnetic Fields ◽  
Growth Rates ◽  
Dynamo Action ◽  
Numerical Evidence ◽  
Shear Mechanism ◽  
Field Lines

Fast dynamo models based on cat maps with shear are introduced. With an appropriate choice of shear even and odd magnetic fields evolve independently. Fast dynamo action occurs for even fields in the absence of shear; the introduction of shear introduces cancellations and modifies growth rates. An odd field may be considered as lying in a disc and evolving under a pseudo-Anosov map, which stretches and folds field but does not reconnect field lines. Without shear odd fields decay, but non-trivial shear allows fast amplification of field by the stretch–fold–shear mechanism. Numerical evidence is presented showing that these models can act as fast dynamos for both even and odd fields. The limit of large stretching by the cat map is considered and proofs of fast dynamo action in this limit are presented.

Planetary Magnetic Fields and Dynamos

2019 ◽  
Author(s):  
Ulrich R. Christensen
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Thermal Evolution ◽  
Rotation Axis ◽  
Space Environment ◽  
Conducting Layer ◽  
Iron Core ◽  
Complex Flow ◽  
Dynamo Theory

Since 1973 space missions carrying vector magnetometers have shown that most, but not all, solar system planets have a global magnetic field of internal origin. They have also revealed a surprising diversity in terms of field strength and morphology. While Jupiter’s field, like that of Earth, is dominated by a dipole moderately tilted relative to the planet’s spin axis, the fields of Uranus and Neptune are multipole-dominated, whereas those of Saturn and Mercury are highly symmetric relative to the rotation axis. Planetary magnetism originates from a dynamo process, which requires a fluid and electrically conducting region in the interior with sufficiently rapid and complex flow. The magnetic fields are of interest for three reasons: (i) they provide ground truth for dynamo theory, (ii) the magnetic field controls how the planet interacts with its space environment, for example, the solar wind, and (iii) the existence or nonexistence and the properties of the field enable us to draw inferences on the constitution, dynamics, and thermal evolution of the planet’s interior. Numerical simulations of the geodynamo, in which convective flow in a rapidly rotating spherical shell representing the outer liquid iron core of the Earth leads to induction of electric currents, have successfully reproduced many observed properties of the geomagnetic field. They have also provided guidelines on the factors controlling magnetic field strength and morphology. For numerical reasons the simulations must employ viscosities far greater than those inside planets and it is debatable whether they capture the correct physics of planetary dynamo processes. Nonetheless, such models have been adapted to test concepts for explaining magnetic field properties of other planets. For example, they show that a stable stratified conducting layer above the dynamo region is a plausible cause for the strongly axisymmetric magnetic fields of Mercury or Saturn.

Sign in / Sign up

Export Citation Format

Share Document