scholarly journals A numerical study on magnetic polarity transition in an MHD dynamo model

2007 ◽  
Vol 59 (7) ◽  
pp. 665-673 ◽  
Author(s):  
Futoshi Takahashi ◽  
Masaki Matsushima ◽  
Yoshimori Honkura
Keyword(s):  
Numerical Study ◽  
Magnetic Polarity ◽  
Dynamo Model ◽  
Mhd Dynamo ◽  
Polarity Transition

scholarly journals Details of Magnetic Polarity Transition Recorded in Chinese Loess.

1993 ◽  
Vol 45 (4) ◽  
pp. 289-299 ◽  
Author(s):  
Rixiang Zhu ◽  
Zhongli Ding ◽  
Hanning Wu ◽  
Baochun Huang ◽  
Li Jiang
Keyword(s):  
Magnetic Polarity ◽  
Chinese Loess ◽  
Polarity Transition

Phase-lagged warming and the disruption of climatic rhythms during the Matuyama–Brunhes magnetic polarity transition

2012 ◽  
Vol 21 (2-3) ◽  
pp. 595-600 ◽  
Author(s):  
Ikuko Kitaba ◽  
Masayuki Hyodo ◽  
Shigehiro Katoh ◽  
Mariko Matsushita
Keyword(s):  
Magnetic Polarity ◽  
Polarity Transition

Effects of boundary layers on magnetic field behavior in an MHD dynamo model

2001 ◽  
Vol 128 (1-4) ◽  
pp. 149-161 ◽  
Author(s):  
F. Takahashi ◽  
J.S. Katayama ◽  
M. Matsushima ◽  
Y. Honkura
Keyword(s):  
Magnetic Field ◽  
Boundary Layers ◽  
Dynamo Model ◽  
Field Behavior ◽  
Mhd Dynamo

scholarly journals A shell model for turbulent dynamos

2010 ◽  
Vol 6 (S274) ◽  
pp. 159-161
Author(s):  
G. Nigro ◽  
D. Perrone ◽  
P. Veltri
Keyword(s):  
Shell Model ◽  
Large Scale ◽  
Nonlinear Behavior ◽  
Magnetic Polarity ◽  
Dynamo Model ◽  
Small Scale ◽  
Natural Systems ◽  
Large Scale Magnetic Field ◽  
Time Correlations ◽  
Long Time

AbstractA self-consistent nonlinear dynamo model is presented. The nonlinear behavior of the plasma at small scale is described by using a MHD shell model for fields fluctuations; this allow us to study the dynamo problem in a large parameter regime which characterizes the dynamo phenomenon in many natural systems and which is beyond the power of supercomputers at today. The model is able to reproduce dynamical situations in which the system can undergo transactions to different dynamo regimes. In one of these the large-scale magnetic field jumps between two states reproducing the magnetic polarity reversals. From the analysis of long time series of reversals we infer results about the statistics of persistence times, revealing the presence of hidden long-time correlations in the chaotic dynamo process.

scholarly journals Hysteresis cycle in a turbulent, spherically bounded MHD dynamo model

2009 ◽  
Vol 11 (1) ◽  
pp. 013027 ◽  
Author(s):  
Klaus Reuter ◽  
Frank Jenko ◽  
Cary B Forest
Keyword(s):  
Dynamo Model ◽  
Hysteresis Cycle ◽  
Mhd Dynamo

scholarly journals Fluctuation dynamo in a weakly collisional plasma

2020 ◽  
Vol 86 (5) ◽  
Author(s):  
D. A. St-Onge ◽  
M. W. Kunz ◽  
J. Squire ◽  
A. A. Schekochihin
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Numerical Study ◽  
Collisional Plasma ◽  
Mhd Equations ◽  
Saturated State ◽  
Mhd Dynamo ◽  
Pressure Anisotropy ◽  
Field Lines ◽  
The Magnetic Field

The turbulent amplification of cosmic magnetic fields depends upon the material properties of the host plasma. In many hot, dilute astrophysical systems, such as the intracluster medium (ICM) of galaxy clusters, the rarity of particle–particle collisions allows departures from local thermodynamic equilibrium. These departures – pressure anisotropies – exert anisotropic viscous stresses on the plasma motions that inhibit their ability to stretch magnetic-field lines. We present an extensive numerical study of the fluctuation dynamo in a weakly collisional plasma using magnetohydrodynamic (MHD) equations endowed with a field-parallel viscous (Braginskii) stress. When the stress is limited to values consistent with a pressure anisotropy regulated by firehose and mirror instabilities, the Braginskii-MHD dynamo largely resembles its MHD counterpart, particularly when the magnetic field is dynamically weak. If instead the parallel viscous stress is left unabated – a situation relevant to recent kinetic simulations of the fluctuation dynamo and, we argue, to the early stages of the dynamo in a magnetized ICM – the dynamo changes its character, amplifying the magnetic field while exhibiting many characteristics reminiscent of the saturated state of the large-Prandtl-number ( ${Pm}\gtrsim {1}$ ) MHD dynamo. We construct an analytic model for the Braginskii-MHD dynamo in this regime, which successfully matches simulated dynamo growth rates and magnetic-energy spectra. A prediction of this model, confirmed by our numerical simulations, is that a Braginskii-MHD plasma without pressure-anisotropy limiters will not support a dynamo if the ratio of perpendicular and parallel viscosities is too small. This ratio reflects the relative allowed rates of field-line stretching and mixing, the latter of which promotes resistive dissipation of the magnetic field. In all cases that do exhibit a viable dynamo, the generated magnetic field is organized into folds that persist into the saturated state and bias the chaotic flow to acquire a scale-dependent spectral anisotropy.

scholarly journals A magnetic polarity transition recorded in a 41m granitic core from Takasegawa valley, Nagano prefecture, Japan.

1989 ◽  
Vol 41 (1) ◽  
pp. 137-145
Author(s):  
Haruaki ITO ◽  
Kanichi MOMOSE ◽  
Katsuyasu TOKIEDA ◽  
Yukio NOTSU
Keyword(s):  
Magnetic Polarity ◽  
Nagano Prefecture ◽  
Polarity Transition

Magnetization and suitability for paleomagnetic field intensity measurements of selected samples from sites 332, 334, and 335 of Leg 37 DSDP

1977 ◽  
Vol 14 (4) ◽  
pp. 745-755 ◽  
Author(s):  
C. M. Carmichael
Keyword(s):  
Field Intensity ◽  
Single Unit ◽  
Thick Layer ◽  
Magnetic Polarity ◽  
Small Samples ◽  
Visual Examination ◽  
Field Reversal ◽  
Intensity Measurements ◽  
Polarity Transition ◽  
Partial Reversal

The magnetic properties of 31 small samples from sites 332, 334, and 335 of Leg 37 DSDP were measured, and attempts were made to determine paleomagnetic field intensity. Values of paleointensity of 0.5 and 0.7 times the present field were obtained using one sample from site 332 and one from Site 335 respectively. All of the remaining samples proved unsuitable for paleointensity determinations owing to alteration on heating. This alteration is of two types: (1) destruction of maghemite, which reduces the magnetization of the samples, and (2) a process that markedly increases their thermal and saturation remanences and which may involve precipitation of new small magnetic grains out of glass. A 19 m thick layer at a depth of about 600 m in hole 332B, which appears to be a single unit on the basis of visual examination and chemical analysis of samples, contains a magnetic polarity transition. This may be due to a field reversal, or a partial reversal, while the unit was being implaced. Only samples from site 335 have a magnetization that can account for the surface anomaly by the remanence of the layers drilled.

Solar Internal Rotation and Dynamo Waves: A Two-Dimensional Asymptotic Solution in the Convection Zone

2000 ◽  
Vol 179 ◽  
pp. 379-380
Author(s):  
Gaetano Belvedere ◽  
Kirill Kuzanyan ◽  
Dmitry Sokoloff
Keyword(s):  
Magnetic Field ◽  
Asymptotic Solution ◽  
Internal Rotation ◽  
Convection Zone ◽  
General Idea ◽  
Dynamo Model ◽  
Axially Symmetric ◽  
Dynamo Action ◽  
Regeneration Rate ◽  
Dynamo Waves

Extended abstractHere we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone. We calculate here a spatial 2-D structure of the mean magnetic field, adopting real profiles of the solar internal rotation (the Ω-effect) and an extended prescription of the turbulent α-effect. In our model assumptions we do not prescribe any meridional flow that might seriously affect the resulting generated magnetic fields. We do not assume apriori any region or layer as a preferred site for the dynamo action (such as the overshoot zone), but the location of the α- and Ω-effects results in the propagation of dynamo waves deep in the convection zone. We consider an axially symmetric magnetic field dynamo model in a differentially rotating spherical shell. The main assumption, when using asymptotic WKB methods, is that the absolute value of the dynamo number (regeneration rate) |D| is large, i.e., the spatial scale of the solution is small. Following the general idea of an asymptotic solution for dynamo waves (e.g., Kuzanyan & Sokoloff 1995), we search for a solution in the form of a power series with respect to the small parameter |D|–1/3(short wavelength scale). This solution is of the order of magnitude of exp(i|D|1/3S), where S is a scalar function of position.

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