scholarly journals Twisted Magnetic Fields in Conducting Fluids

1954 ◽  
Vol 7 (1) ◽  
pp. 5 ◽  
Author(s):  
JW Dungey ◽  
RE Loughhead
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Normal Modes ◽  
Loop Formation ◽  
Twisted Field ◽  
Conducting Fluids ◽  
Lines Of Force

The formation of loops in the lines of force of a twisted magnetic field confined within a cylinder of radius R, first suggested by AIfv�n (1950a), is discussed by the method of normal modes. The model first becomes unstable with respect to modes which do not lead to the formation of loops. Ignoring this, the condition obtained for loop formation is that the pitch of the twisted field be less than pR.

3. Spots and magnetic fields

2020 ◽  
pp. 65-99
Author(s):  
Philip Judge
Keyword(s):  
Magnetic Field ◽  
Magnetic Properties ◽  
Magnetic Fields ◽  
Solar Interior ◽  
Solar Dynamo ◽  
The Sun ◽  
Electrically Conducting ◽  
New Science ◽  
The 1960S ◽  
Conducting Fluids

‘Spots and magnetic fields’ explores sunspot behaviour. We have known since 1908 that sunspots are magnetic, but why does the Sun form them at all? Is the Sun extraordinary in this, or is its behaviour in line with other stars? The Sun’s magnetic field is generated by a solar dynamo, which can be partly explained by magnetohydrodynamics (MHD)—the study of the magnetic properties and behaviour of electrically conducting fluids—however, there is no full consensus on the solar dynamo. In the 1960s the new science of helioseismology gave us insights into the Sun’s interior rotation, but we are unable to make truly critical observations in the solar interior.

Twist of Magnetic Fields in Solar Active Regions

2000 ◽  
Vol 179 ◽  
pp. 245-247
Author(s):  
Hongqi Zhang ◽  
Lirong Tian ◽  
Shudong Bao ◽  
Mei Zhang
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Northern Hemisphere ◽  
General Trend ◽  
Active Regions ◽  
Astronomical Observatory ◽  
Twisted Field ◽  
Current Helicity ◽  
Sunspot Groups

Extended abstractIn the solar atmosphere, the magnetic and current helicity have played an important role in the study of twisted magnetic field. Current helicity parameterh∥=B∥· (∇ ×B)∥and force free factorcan be used to analyze the distribution of twisted field (current helicity) in the photosphere (Seehafer 1990; Pevtsovet al.1995; Bao & Zhang 1998). Bao & Zhang (1998) and Zhang & Bao (1999) computed the photospheric current helicity parameterh∥for 422 active regions, including most of the large ones observed in the period of 1988–1997 at Huairou Solar Observing Station of Beijing Astronomical Observatory.The calculated results (Pevtsovet al.1995; Abramenkoet al.1996; Bao & Zhang 1998) show that most current helicities in sunspot groups in the northern hemisphere show negative sign in the northern hemisphere, while positive in the southern hemisphere, which is consistent with Seehafer’s result (Seehafer 1990). The distribution of current helicity parameterh∥in active regions also shows the butterfly pattern through the solar cycle. And, less than 30% of the active regions do not follow the general trend (Zhang & Bao 1998).

scholarly journals PENGGUNAAN MEDIA JARUM BERGOYANG DALAM MATERI MEDAN MAGNET UNTUK MENINGKATKAN PEMAHAMAN KONSEP PESERTA DIDIK

2021 ◽  
Vol 1 (2) ◽  
pp. 159-167
Author(s):  
BUDI HENDRATNO
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Force ◽  
Assembly Process ◽  
The Media ◽  
Three Stages ◽  
Line Trajectory ◽  
Magnetic Poles ◽  
Lines Of Force

The purpose of this paper is to further improve students' understanding of the concept of magnetic fields, by creating media that can show the characteristics of magnetic fields, which are abstract quantities and vector quantities. This media is designed in addition to being able to prove the existence of an abstract magnetic field, it can also show the direction of the magnetic lines of force, show the shape of the curved trajectory of the magnetic lines of force, and can directly determine the magnetic poles if the magnet is made by electromagnetic means. While the media that is often used so far can only prove its existence. The process of making this media through three stages, namely; design, assemble and test. This media is designed by using a needle that is placed above the water and brought close to a magnet with the media term "Jarum Bergoyang". The assembly process uses simple tools and easily available materials. The testing process was carried out on magnetic practicum activities by class IX-C students of SMP Negeri 2 Saketi 2015. The results of the practicum can be concluded that swaying needle media can be used to prove the existence of a magnetic field, can determine the direction of magnetic force lines, can show the shape of the line trajectory. magnetic lines of force and can directly show the magnetic poles of the coil. ABSTRAKTujuan dari penulisan ini adalah untuk lebih meningkatkan pemahaman siswa terhadap konsep medan magnet, dengan membuat media yang dapat menunjukan karakteristik medan magnet, yang merupakan besaran yang bersifat abstrak dan besaran vektor. Media ini dirancang selain bisa membuktikan keberadaan medan magnet yang bersifat abstrak, juga dapat menunjukan arah garis-garis gaya magnet, menunjukan bentuk lintasan lengkung garis-garis gaya magnet, dan bisa secara langsung menentukan kutub-kutub magnet apabila magnetnya itu dibuat dengan cara elektromagnetik. Sementara media yang sering dipakai selama ini hanya dapat membuktikan keberadaannya saja. Proses pembuatan media ini melalui tiga tahapan yaitu ; merancang, merakit dan menguji. Media ini dirancang dengan menggunakan jarum yang ditempatkan di atas air dan didekatkan dengan magnet dengan istilah media jarum bergoyang. Proses perakitan menggunakan alat yang sederhana dan bahan yang mudah didapat. Proses pengujian dilakukan pada kegiatan praktikum kemagnetan oleh siswa kelas IX-C SMP Negeri 2 Saketi Tahun 2015. Hasil praktikum dapat disimpulkan bahwa media jarum bergoyang dapat digunakan untuk membuktikan adanya medan magnet, dapat menentukan arah garis-garis gaya magnet, dapat menunjukan bentuk lintasan garis-garis gaya magnet dan dapat secara langsung menunjukan kutub-kutub magnet kumparan.

MHD Analysis of the Evolution of Solar Magnetic Fields and Currents in an Active Region

1985 ◽  
Vol 107 ◽  
pp. 487-490
Author(s):  
S. T. Wu ◽  
J. F. Wang ◽  
E. Tandberg-Hanssen
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Magnetic Energy ◽  
Neutral Line ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Solar Magnetic Fields ◽  
Twisted Field ◽  
The Magnetic Field

We have used a self-consistent magnetohydrodynamics model to study the evolution of solar magnetic fields in an active region. The problem has been cast as an initial boundary-value problem based on explicit mathematical formalism (i.e., method of projected characteristics), whereby a variety of horizontal photospheric motions can be treated. In this paper we deal specifically with photospheric shear motions in the active region. Our results show the evolution of the magnetic energy, the electric current systems, including the distributions of J⊥ (current perpendicular to the magnetic field) J| (current parallel to the magnetic field), the magnetic field configuration and a comparison between the build-up of magnetic energy in a pre-twisted field and in an initial untwisted field due to photospheric shearing motions. From these results we conclude that the energy build-up is confined within a certain region near the neutral line at the photospheric level. The possible location of the particle acceleration also can be studied.

Der Gyro-Relaxations-Effekt

1957 ◽  
Vol 12 (10) ◽  
pp. 822-825 ◽  
Author(s):  
A. Schlüter
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Degrees Of Freedom ◽  
Extreme Temperatures ◽  
Heating Mechanism ◽  
The Magnetic Field ◽  
Lines Of Force

Es wird gezeigt, daß ständig eine Relaxation der Freiheitsgrade der Bewegung entlang den magnetischen Feldlinien relativ zu den Freiheitsgraden der Umlaufsbewegueg um diese magnetischen Feldlinien eintritt, wenn die Stärke des Magnetfeldes mit der Zeit oder längs der Feldlinien sich ändert. Diese Relaxation führt zu einem Temperaturanstieg des Plasmas und zwar auch dann, wenn die magnetischen Feldänderungen periodisch erfolgen. Dieser Prozeß dürfte einen günstigen Heizungsmechanismus darstellen, um zu extrem hohen Temperaturen zu gelangen.It is shown that a relaxation of the degrees of freedom of the motion along the lines of force of a magnetic field relative to those of the gyration around these lines always occurs if the strength of the magnetic fields changes with time or along the trajectories. This relaxation causes an increase in the temperature of a plasma, even if the magnetic field changes are periodic, and may represent a convenient heating mechanism for achieving extreme temperatures.

On the re-connexion of magnetic lines of force

1973 ◽  
Vol 9 (3) ◽  
pp. 409-427 ◽  
Author(s):  
Shoichiro Fukao ◽  
Takao Tsuda
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Two Dimensions ◽  
Neutral Point ◽  
Transition Layers ◽  
Finite Electrical Conductivity ◽  
External Conditions ◽  
The Magnetic Field ◽  
Conducting Fluids ◽  
Lines Of Force

The magnetic field and flow with an X-type neutral point or stagnation point are studied numerically for the steady state of incompressible, finitely conducting, viscous fluid in two dimensions. There appear two transition layers connecting smoothly the regions on either side, each of which contains almost uniform magnetic field and flow. The electric currents are concentrated in the vicinity of the neutral point and along the transition layers. The magnetic field is regarded as almost frozen in the fluid in other current-free regions, even in the case of moderate conductivities. The current-core over the neutral point is accompanied by a remarkable shear of currents, which may contribute to reducing the local electrical conductivity effectively. Thus the re-connexion of magnetic lines of force may be possible even in very highly conducting fluids. It is shown that the re-connexion is not essentially influenced by dissipations due to finite electrical conductivity or viscosity, but definitely by external conditions such as the applied electric field in the magnetic field and flow.

Magnetic field intermittency and fast dynamo action in random helical flows

1992 ◽  
Vol 241 ◽  
pp. 199-214 ◽  
Author(s):  
Andrew D. Gilbert ◽  
B. J. Bayly
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Growth Rates ◽  
Molecular Diffusion ◽  
Normal Modes ◽  
Magnetic Helicity ◽  
Dynamo Action ◽  
Random Flows

The evolution of passive magnetic fields is considered in random flows made up of single helical waves. In the absence of molecular diffusion the growth rates of all moments of a magnetic field are calculated analytically, and it is found that the field becomes increasingly intermittent with time. The evolution of normal modes of the ensemble-averaged field is determined; it is shown that the flows considered give fast dynamo action, and magnetic field modes with either sign of magnetic helicity may grow.

scholarly journals Introduction to Fountains, Wind, Infall (and Magnetic Fields and Dynamo Mechanisms)

1991 ◽  
Vol 144 ◽  
pp. 1-11 ◽  
Author(s):  
F. D. Kahn
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Galactic Disk ◽  
Fountain Flow ◽  
Hot Gas ◽  
And Topology ◽  
Set Up ◽  
Ionization Balance ◽  
The Magnetic Field ◽  
Lines Of Force

The galactic fountain is formed by hot gas rising from the galactic disk. The lines of force of the interstellar magnetic field are dragged along in the flow. This lecture deals with the geometry and topology of the configuration of the field that is set up. The fountain flow acts as a dynamo, and the presence of the magnetic field plays an important part in the ionization balance of the gas as it returns towards the disk.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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