Turbulent transport coefficients and residual energy in mean-field dynamo theory

2008 ◽  
Vol 15 (2) ◽  
pp. 022302 ◽  
Author(s):  
Fujihiro Hamba ◽  
Hisanori Sato
Keyword(s):  
Turbulent Transport ◽  
Transport Coefficients ◽  
Mean Field ◽  
Residual Energy ◽  
Dynamo Theory ◽  
Mean Field Dynamo

scholarly journals Turbulent transport coefficients in galactic dynamo simulations using singular value decomposition

2019 ◽  
Vol 491 (3) ◽  
pp. 3870-3883 ◽  
Author(s):  
Abhijit B Bendre ◽  
Kandaswamy Subramanian ◽  
Detlef Elstner ◽  
Oliver Gressel
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Turbulent Transport ◽  
Transport Coefficients ◽  
Mean Field ◽  
Dynamo Model ◽  
The Mean ◽  
Value Decomposition ◽  
Svd Method ◽  
Mean Field Dynamo

ABSTRACT Coherent magnetic fields in disc galaxies are thought to be generated by a large-scale (or mean-field) dynamo operating in their interstellar medium. A key driver of mean magnetic field growth is the turbulent electromotive force (EMF), which represents the influence of correlated small-scale (or fluctuating) velocity and magnetic fields on the mean field. The EMF is usually expressed as a linear expansion in the mean magnetic field and its derivatives, with the dynamo tensors as expansion coefficients. Here, we adopt the singular value decomposition (SVD) method to directly measure these turbulent transport coefficients in a simulation of the turbulent interstellar medium that realizes a large-scale dynamo. Specifically, the SVD is used to least-square fit the time series data of the EMF with that of the mean field and its derivatives, to determine these coefficients. We demonstrate that the spatial profiles of the EMF reconstructed from the SVD coefficients match well with that taken directly from the simulation. Also, as a direct test, we use the coefficients to simulate a 1D mean-field dynamo model and find an overall similarity in the evolution of the mean magnetic field between the dynamo model and the direct simulation. We also compare the results with those which arise using simple regression and the ones obtained previously using the test-field method, to find reasonable qualitative agreement. Overall, the SVD method provides an effective post-processing tool to determine turbulent transport coefficients from simulations.

scholarly journals Magnetic Cycles and Rotation in Active Late–Type Stars

2004 ◽  
Vol 215 ◽  
pp. 289-291
Author(s):  
Ilkka Tuominen ◽  
Svetlana V. Berdyugina ◽  
Maarit J. Korpi
Keyword(s):  
Mean Field ◽  
Point Of View ◽  
Doppler Imaging ◽  
Late Type ◽  
Dynamo Theory ◽  
Flip Flop ◽  
Cyclic Behaviour ◽  
Magnetic Cycles ◽  
Mean Field Dynamo

Observational evidence, based both on spectroscopic Doppler imaging and long-term photometry, of strongly nonaxisymmetric spot distributions in magnetically very active late-type stars, with a special cyclic behaviour (the “flip-flop” effect), is presented. Theoretical implications of these results are discussed from the point of view of nonlinear mean-field dynamo theory.

Existence and Energy Balance of the Solar Dynamo

1993 ◽  
Vol 157 ◽  
pp. 19-23
Author(s):  
J.H.G.M. van Geffen
Keyword(s):  
Magnetic Field ◽  
Energy Balance ◽  
Energy Method ◽  
Magnetic Energy ◽  
Mean Field ◽  
Solar Dynamo ◽  
Ensemble Averaging ◽  
Dynamo Theory ◽  
The Magnetic Field ◽  
Mean Field Dynamo

The idea behind the use of ensemble averaging and the finite magnetic energy method of van Geffen and Hoyng (1992) is briefly discussed. Applying this method to the solar dynamo shows that the turbulence — an essential ingredient of traditional mean field dynamo theory — poses grave problems: the turbulence makes the magnetic field so unstable that it becomes impossible to recognize any period.

scholarly journals On the mean-field theory of the Karlsruhe Dynamo Experiment

2002 ◽  
Vol 9 (3/4) ◽  
pp. 171-187 ◽  
Author(s):  
K.-H. Rädler ◽  
M. Rheinhardt ◽  
E. Apstein ◽  
H. Fuchs
Keyword(s):  
Field Theory ◽  
Key Words ◽  
Mean Field Theory ◽  
Mean Field ◽  
Experimental Results ◽  
Dynamo Theory ◽  
The Mean ◽  
Earth’S Interior ◽  
Earth's Interior ◽  
Mean Field Dynamo

Abstract. In the Forschungszentrum Karlsruhe an experiment has been constructed which demonstrates a homogeneous dynamo as is expected to exist in the Earth's interior. This experiment is discussed within the framework of mean-field dynamo theory. The main predictions of this theory are explained and compared with the experimental results. Key words. Dynamo, geodynamo, dynamo experiment, mean-field dynamo theory, a-effect

Non-Local Mean Field Dynamo Theory and Magnetic Fronts in Galaxies

2003 ◽  
Vol 97 (2) ◽  
pp. 135-148 ◽  
Author(s):  
Sergei Fedotov ◽  
Alexey Ivanov ◽  
Andrey Zubarev
Keyword(s):  
Mean Field ◽  
Dynamo Theory ◽  
Local Mean ◽  
Non Local ◽  
Mean Field Dynamo

scholarly journals HALL CURRENT EFFECTS IN MEAN-FIELD DYNAMO THEORY

2016 ◽  
Vol 829 (1) ◽  
pp. 51 ◽  
Author(s):  
Manasvi Lingam ◽  
Amitava Bhattacharjee
Keyword(s):  
Hall Current ◽  
Mean Field ◽  
Dynamo Theory ◽  
Mean Field Dynamo
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