scholarly journals Formation of Solar Prominences with Normal and Inverse Polarities

1993 ◽  
Vol 141 ◽  
pp. 138-142
Author(s):  
G. S. Choe ◽  
L. C. Lee
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Thermal Instability ◽  
Dynamic Evolution ◽  
Solar Prominence ◽  
Solar Prominences

AbstractNumerical simulations of solar prominence formation are presented employing photospheric horizontal motions as boundary conditions. Three different combinations of magnetic field configurations and footpoint motions are considered: (1) a bipolar arcade with a footpoint shear, (2) an arcade exposed to a shearing and converging motion, (3) two adjacent arcades undergoing a shearing and converging motion. In each case, it is found that the dynamic evolution of magnetic fields can force the plasma into a thermal instability leading to the formation of a prominence.

scholarly journals Simulation Studies of Solar Prominence Formation

1998 ◽  
Vol 167 ◽  
pp. 278-281
Author(s):  
G.S. Choe ◽  
C.Z. Cheng
Keyword(s):  
Numerical Simulations ◽  
Thermal Instability ◽  
Coronal Plasma ◽  
Simulation Studies ◽  
Solar Prominence ◽  
Solar Prominences ◽  
Different Types

AbstractA series of numerical simulations are presented for formation of solar prominences. We have investigated the dynamic and thermodynamic evolution of coronal plasma in response to photospheric horizontal motions. In three different setups of field configurations and footpoint motions, different types of prominences are found to be formed by thermal instability.

scholarly journals Multiscale structures and noise in magnetized plasmas line-tied at conducting surfaces

2019 ◽  
Vol 85 (2) ◽  
Author(s):  
A. B. Hassam ◽  
Yi-Min Huang
Keyword(s):  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Magnetized Plasma ◽  
Long Wavelength ◽  
Numerical Noise ◽  
Long Time ◽  
Multiscale Structures ◽  
Ideal Magnetohydrodynamic ◽  
Numerical And Analytical Methods

In magnetized plasma situations where magnetic fields intersect massive conducting boundaries, ‘line-tied’ boundary conditions are often used, analytically and in numerical simulations. For ideal magnetohydrodynamic (MHD) plasmas, these conditions are arrived at given the relatively long time scales for magnetic fields penetrating resistively into good conductors. Under line-tied boundary conditions, numerical simulations often exhibit what could be construed as numerical ‘noise’ emanating from the boundaries. We show here that this ‘noise’ is real. By combining numerical and analytical methods, we highlight the existence of sharp spatial structures near the conductors and confirm the appearance of short wavelength structures riding on long wavelength modes. We conclude that, for numerical fidelity, the short multiscale structures need to be resolved. Generally, the short structure widths scale as the square root of the plasma $\unicode[STIX]{x1D6FD}$.

Exact equilibria for nonlinear force-free magnetic fields with its applications to astrophysics and fusion plasmas

2014 ◽  
Vol 80 (2) ◽  
pp. 173-195 ◽  
Author(s):  
S. M. Moawad
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Physics ◽  
Coronal Magnetic Field ◽  
Fusion Plasmas ◽  
Magnetic Structures ◽  
Magnetic Flux Ropes ◽  
Solar Prominences ◽  
Confinement Fusion ◽  
Nonlinear Force

AbstractKnowledge of the structure of coronal magnetic field originating from the photosphere is relevant to the understanding of many solar activity phenomena, e.g. flares, solar prominences, coronal loops, and coronal heating. In most of the existing literature, these loop-like magnetic structures are modeled as force-free magnetic fields (FFMF) without any plasma flow. In this paper, we present several exact solution classes for nonlinear FFMF, in both translational and axisymmetric geometries. The solutions are considered for their possible relevance to astrophysics and solar physics problems. These are used to illustrate arcade-type magnetic field structures of the photosphere and twisted magnetic flux ropes through the coronal mass ejections (CMEs), as well as magnetic confinement fusion plasmas.

scholarly journals The Effect of Small Scale Motion on an Essentially-Nonlinear Dynamo

2010 ◽  
Vol 6 (S271) ◽  
pp. 367-368
Author(s):  
Benjamin M. Byington ◽  
Nicholas H. Brummell ◽  
Steven M. Tobias
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Numerical Simulations ◽  
Small Scale ◽  
Local Velocity ◽  
Dissipative Effects ◽  
Dynamo Mechanism ◽  
New Type ◽  
Scale Motion

AbstractA dynamo is a process by which fluid motions sustain magnetic fields against dissipative effects. Dynamos occur naturally in many astrophysical systems. Theoretically, we have a much more robust understanding of the generation and maintenance of magnetic fields at the scale of the fluid motions or smaller, than that of magnetic fields at scales much larger than the local velocity. Here, via numerical simulations, we examine one example of an “essentially nonlinear” dynamo mechanism that successfully maintains magnetic field at the largest available scale (the system scale) without cascade to the resistive scale. In particular, we examine whether this new type of dynamo at the system scale is still effective in the presence of other smaller-scale dynamics (turbulence).

scholarly journals Computing nonlinear force free coronal magnetic fields

2003 ◽  
Vol 10 (4/5) ◽  
pp. 313-322 ◽  
Author(s):  
T. Wiegelmann ◽  
T. Neukirch
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Random Noise ◽  
Coronal Magnetic Field ◽  
Optimization Method ◽  
Numerical Code ◽  
Coronal Magnetic Fields ◽  
Nonlinear Force ◽  
Free Fields

Abstract. Knowledge of the structure of the coronal magnetic field is important for our understanding of many solar activity phenomena, e.g. flares and CMEs. However, the direct measurement of coronal magnetic fields is not possible with present methods, and therefore the coronal field has to be extrapolated from photospheric measurements. Due to the low plasma beta the coronal magnetic field can usually be assumed to be approximately force free, with electric currents flowing along the magnetic field lines. There are both observational and theoretical reasons which suggest that at least prior to an eruption the coronal magnetic field is in a nonlinear force free state. Unfortunately the computation of nonlinear force free fields is way more difficult than potential or linear force free fields and analytic solutions are not generally available. We discuss several methods which have been proposed to compute nonlinear force free fields and focus particularly on an optimization method which has been suggested recently. We compare the numerical performance of a newly developed numerical code based on the optimization method with the performance of another code based on an MHD relaxation method if both codes are applied to the reconstruction of a semi-analytic nonlinear force-free solution. The optimization method has also been tested for cases where we add random noise to the perfect boundary conditions of the analytic solution, in this way mimicking the more realistic case where the boundary conditions are given by vector magnetogram data. We find that the convergence properties of the optimization method are affected by adding noise to the boundary data and we discuss possibilities to overcome this difficulty.

scholarly journals Quasi-Static Evolution of a Force-Free Magnetic Field and Conditions for the Onset of a Stellar Flare

1989 ◽  
Vol 104 (2) ◽  
pp. 259-263
Author(s):  
J.J. Aly
Keyword(s):  
Magnetic Field ◽  
Boundary Conditions ◽  
Solar Corona ◽  
Solar Physics ◽  
Short Interval ◽  
Dynamic Evolution ◽  
Theoretical Problem ◽  
Limited Extent ◽  
Stellar Flare ◽  
Photospheric Level

Magnetic fields in the solar corona are braught into an endless evolution by the never-ceasing motions of the subphotospheric plasma in which the feet of their lines are anchored. It is generally thought that this evolution is essentially quasi-static, the field passing through a sequence of force-free equilibrium states. Sporadically, however, the equilibrium is broken in a region of limited extent, and during a relatively short interval of time a catastrophic highly dynamic evolution takes place, giving rise to such wellknown phenomena as flares or coronal transients. Understanding the factors which determine if a magnetohydrostatic coronal equilibrium is maintained or, on the contrary, destroyed, when boundary conditions change at the photospheric level, then appears as a central theoretical problem of solar physics. In this Communication, we report some recent results which shed some new light onto this old problem.

Linear Buckling and Vibration Behavior of Piezoelectric/Piezomagnetic Beam under Uniform Magnetic Field

2014 ◽  
Vol 592-594 ◽  
pp. 2071-2075 ◽  
Author(s):  
A. Kumaravel ◽  
J. Jones Praveen ◽  
Raju Sethuraman ◽  
A. Arockiarajan
Keyword(s):  
Magnetic Field ◽  
Finite Element Method ◽  
Finite Element ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Constitutive Equations ◽  
Uniform Magnetic Field ◽  
Vibration Behavior ◽  
Linear Buckling ◽  
Piezoelectric Coupling

The constitutive equations of MEE materials are used to derive the finite element equations involving the coupling between mechanical, electrical and magnetic fields. The candidate materials for this study are piezoelectric (BaTiO3) and magnetostrictive (CoFe2O4) material. The linear buckling and vibration behavior of layered MEE beam under uniform magnetic field is carried out using finite element method. The present study is limited to clamped-clamped boundary conditions. The influence of stacking sequences and piezoelectric coupling on critical buckling magnetic field and vibration behaviour is investigated.

scholarly journals Dynamically dominant magnetic fields in the diffuse interstellar medium

2008 ◽  
Vol 4 (S259) ◽  
pp. 87-88 ◽  
Author(s):  
Andrew Fletcher ◽  
M. Korpi ◽  
A. Shukurov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Interstellar Medium ◽  
Numerical Simulations ◽  
Hydrodynamic Model ◽  
Mass Conservation ◽  
Unstable Flow ◽  
Gas Density ◽  
The Magnetic Field

AbstractObservations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.

scholarly journals Magnetic Field Reconstruction in a Solar Active Region

2001 ◽  
Vol 203 ◽  
pp. 328-330
Author(s):  
H. Wang ◽  
Y. Yan ◽  
T. Sakurai
Keyword(s):  
Magnetic Field ◽  
Integral Equation ◽  
Active Region ◽  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Technique ◽  
Boundary Integral ◽  
Field Reconstruction ◽  
Coronal Magnetic Fields ◽  
Function Vector

Supposing coronal magnetic fields are in a force-free state from the chromosphere to the height of two solar radii, we reconstruct 3D force-free magnetic fields by making use of a new numerical technique, in which the fields are represented by a boundary integral equation based on a specific Green's function. Vector magnetic fields observed on the photospheric surface can be taken as the boundary conditions of this equation. Magnetic fields in AR8270 on 14 July 1998 were employed as an example to exhibit the capability of this numerical technique.

scholarly journals Striations, integrals, hourglasses, and collapse – thermal instability driven magnetic simulations of molecular clouds

2020 ◽  
Vol 500 (3) ◽  
pp. 2831-2849
Author(s):  
C J Wareing ◽  
J M Pittard ◽  
S A E G Falle
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Adaptive Mesh Refinement ◽  
Thermal Instability ◽  
Initial Conditions ◽  
Power Spectra ◽  
Adaptive Mesh ◽  
Spherical Cloud ◽  
Field Lines ◽  
Self Gravity

ABSTRACT The MHD version of the adaptive mesh refinement (AMR) code, MG, has been employed to study the interaction of thermal instability, magnetic fields, and gravity through 3D simulations of the formation of collapsing cold clumps on the scale of a few parsecs, inside a larger molecular cloud. The diffuse atomic initial condition consists of a stationary, thermally unstable, spherical cloud in pressure equilibrium with lower density surroundings and threaded by a uniform magnetic field. This cloud was seeded with 10 per cent density perturbations at the finest initial grid level around n = 1.1 cm−3 and evolved with self-gravity included from the outset. Several cloud diameters were considered (100, 200, and 400 pc) equating to several cloud masses (17 000, 136 000, and 1.1 × 106 M⊙). Low-density magnetic-field-aligned striations were observed as the clouds collapse along the field lines into disc-like structures. The induced flow along field lines leads to oscillations of the sheet about the gravitational minimum and an integral-shaped appearance. When magnetically supercritical, the clouds then collapse and generate hourglass magnetic field configurations with strongly intensified magnetic fields, reproducing observational behaviour. Resimulation of a region of the highest mass cloud at higher resolution forms gravitationally bound collapsing clumps within the sheet that contain clump-frame supersonic (M ∼ 5) and super-Alfvénic (MA ∼ 4) velocities. Observationally realistic density and velocity power spectra of the cloud and densest clump are obtained. Future work will use these realistic initial conditions to study individual star and cluster feedback.

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