scholarly journals Three-dimensional Simulations of Accretion to Stars with Complex Magnetic Fields

2008 ◽  
Author(s):  
M. Long ◽  
M. M. Romanova ◽  
R. V. E. Lovelace ◽  
Rudy Wijnands ◽  
Diego Altamirano ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Three Dimensional ◽  
Three Dimensional Simulations

scholarly journals Magneto-convection

2012 ◽  
Vol 370 (1970) ◽  
pp. 3070-3087 ◽  
Author(s):  
Robert F. Stein
Keyword(s):  
Magnetic Fields ◽  
Equations Of State ◽  
Three Dimensional ◽  
Dynamo Action ◽  
Spatial And Temporal Scales ◽  
Solar Observations ◽  
Wide Range ◽  
Induction Equation ◽  
The Magnetic Field ◽  
Three Dimensional Simulations

Convection is the transport of energy by bulk mass motions. Magnetic fields alter convection via the Lorentz force, while convection moves the fields via the curl( v × B ) term in the induction equation. Recent ground-based and satellite telescopes have increased our knowledge of the solar magnetic fields on a wide range of spatial and temporal scales. Magneto-convection modelling has also greatly improved recently as computers become more powerful. Three-dimensional simulations with radiative transfer and non-ideal equations of state are being performed. Flux emergence from the convection zone through the visible surface (and into the chromosphere and corona) has been modelled. Local, convectively driven dynamo action has been studied. The alteration in the appearance of granules and the formation of pores and sunspots has been investigated. Magneto-convection calculations have improved our ability to interpret solar observations, especially the inversion of Stokes spectra to obtain the magnetic field and the use of helioseismology to determine the subsurface structure of the Sun.

scholarly journals Three dimensional simulations of Hall magnetohydrodynamics

2010 ◽  
Vol 6 (S274) ◽  
pp. 433-436 ◽  
Author(s):  
Daniel O. Gómez
Keyword(s):  
Magnetic Fields ◽  
Hall Effect ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Mhd Equations ◽  
Hall Parameter ◽  
Astrophysical Objects ◽  
Hall Mhd ◽  
Three Dimensional Simulations

AbstractTurbulent flows take place in a large variety of astrophysical objects, and often times are the source of dynamo generated magnetic fields. Much of the progress in our understanding of dynamo mechanisms, has been made within the theoretical framework of magnetohydrodynamics (MHD). However, for sufficiently diffuse media, the Hall effect eventually becomes non-negligible.We present results from simulations of the Hall-MHD equations. The simulations are performed with a pseudospectral code to achieve exponentially fast convergence. We study the role of the Hall effect in the dynamo efficiency for different values of the Hall parameter.

scholarly journals Can Multi-threaded Flux Tubes in Coronal Arcades Support a Magnetohydrodynamic Avalanche?

Solar Physics ◽  
2021 ◽  
Vol 296 (8) ◽  
Author(s):  
J. Threlfall ◽  
J. Reid ◽  
A. W. Hood
Keyword(s):  
Magnetic Fields ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Flux Tubes ◽  
Single Thread ◽  
Mhd Instabilities ◽  
Mhd Instability ◽  
Mhd Simulations ◽  
Ideal Mhd ◽  
Model Geometry

AbstractMagnetohydrodynamic (MHD) instabilities allow energy to be released from stressed magnetic fields, commonly modelled in cylindrical flux tubes linking parallel planes, but, more recently, also in curved arcades containing flux tubes with both footpoints in the same photospheric plane. Uncurved cylindrical flux tubes containing multiple individual threads have been shown to be capable of sustaining an MHD avalanche, whereby a single unstable thread can destabilise many. We examine the properties of multi-threaded coronal loops, wherein each thread is created by photospheric driving in a realistic, curved coronal arcade structure (with both footpoints of each thread in the same plane). We use three-dimensional MHD simulations to study the evolution of single- and multi-threaded coronal loops, which become unstable and reconnect, while varying the driving velocity of individual threads. Experiments containing a single thread destabilise in a manner indicative of an ideal MHD instability and consistent with previous examples in the literature. The introduction of additional threads modifies this picture, with aspects of the model geometry and relative driving speeds of individual threads affecting the ability of any thread to destabilise others. In both single- and multi-threaded cases, continuous driving of the remnants of disrupted threads produces secondary, aperiodic bursts of energetic release.

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