On the magnetic field line topology in solar active regions

Solar Physics ◽  
1986 ◽  
Vol 105 (2) ◽  
Author(s):  
N. Seehafer
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Active Regions ◽  
Solar Active Regions ◽  
The Magnetic Field

scholarly journals Comparison of the measured and modelled electron densities and temperatures in the ionosphere and plasmasphere during 20-30 January, 1993

2000 ◽  
Vol 18 (10) ◽  
pp. 1257-1262 ◽  
Author(s):  
A. V. Pavlov ◽  
T. Abe ◽  
K.-I. Oyama
Keyword(s):  
Magnetic Field ◽  
Heat Flux ◽  
Electron Temperature ◽  
Field Line ◽  
Electron Density ◽  
Magnetic Field Line ◽  
New Approach ◽  
Additional Heating ◽  
Vibrational Levels ◽  
The Magnetic Field

Abstract. We present a comparison of the electron density and temperature behaviour in the ionosphere and plasmasphere measured by the Millstone Hill incoherent-scatter radar and the instruments on board of the EXOS-D satellite with numerical model calculations from a time-dependent mathematical model of the Earth's ionosphere and plasmasphere during the geomagnetically quiet and storm period on 20–30 January, 1993. We have evaluated the value of the additional heating rate that should be added to the normal photoelectron heating in the electron energy equation in the daytime plasmasphere region above 5000 km along the magnetic field line to explain the high electron temperature measured by the instruments on board of the EXOS-D satellite within the Millstone Hill magnetic field flux tube in the Northern Hemisphere. The additional heating brings the measured and modelled electron temperatures into agreement in the plasmasphere and into very large disagreement in the ionosphere if the classical electron heat flux along magnetic field line is used in the model. A new approach, based on a new effective electron thermal conductivity coefficient along the magnetic field line, is presented to model the electron temperature in the ionosphere and plasmasphere. This new approach leads to a heat flux which is less than that given by the classical Spitzer-Harm theory. The evaluated additional heating of electrons in the plasmasphere and the decrease of the thermal conductivity in the topside ionosphere and the greater part of the plasmasphere found for the first time here allow the model to accurately reproduce the electron temperatures observed by the instruments on board the EXOS-D satellite in the plasmasphere and the Millstone Hill incoherent-scatter radar in the ionosphere. The effects of the daytime additional plasmaspheric heating of electrons on the electron temperature and density are small at the F-region altitudes if the modified electron heat flux is used. The deviations from the Boltzmann distribution for the first five vibrational levels of N2(v) and O2(v) were calculated. The present study suggests that these deviations are not significant at the first vibrational levels of N2 and O2 and the second level of O2, and the calculated distributions of N2(v) and O2(v) are highly non-Boltzmann at vibrational levels v > 2. The resulting effect of N2(v > 0) and O2(v > 0) on NmF2 is the decrease of the calculated daytime NmF2 up to a factor of 1.5. The modelled electron temperature is very sensitive to the electron density, and this decrease in electron density results in the increase of the calculated daytime electron temperature up to about 580 K at the F2 peak altitude giving closer agreement between the measured and modelled electron temperatures. Both the daytime and night-time densities are not reproduced by the model without N2(v > 0) and O2(v > 0), and inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement.Key words: Ionosphere (ionospheric disturbances; ionosphere-magnetosphere interactions; plasma temperature and density)  

scholarly journals The development of magnetic field line wander by plasma turbulence

2017 ◽  
Vol 83 (4) ◽  
Author(s):  
Gregory G. Howes ◽  
Sofiane Bourouaine
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Large Scale ◽  
Magnetic Energy ◽  
Plasma Turbulence ◽  
Alfven Wave ◽  
Astrophysical Plasmas ◽  
Field Lines ◽  
The Magnetic Field

Plasma turbulence occurs ubiquitously in space and astrophysical plasmas, mediating the nonlinear transfer of energy from large-scale electromagnetic fields and plasma flows to small scales at which the energy may be ultimately converted to plasma heat. But plasma turbulence also generically leads to a tangling of the magnetic field that threads through the plasma. The resulting wander of the magnetic field lines may significantly impact a number of important physical processes, including the propagation of cosmic rays and energetic particles, confinement in magnetic fusion devices and the fundamental processes of turbulence, magnetic reconnection and particle acceleration. The various potential impacts of magnetic field line wander are reviewed in detail, and a number of important theoretical considerations are identified that may influence the development and saturation of magnetic field line wander in astrophysical plasma turbulence. The results of nonlinear gyrokinetic simulations of kinetic Alfvén wave turbulence of sub-ion length scales are evaluated to understand the development and saturation of the turbulent magnetic energy spectrum and of the magnetic field line wander. It is found that turbulent space and astrophysical plasmas are generally expected to contain a stochastic magnetic field due to the tangling of the field by strong plasma turbulence. Future work will explore how the saturated magnetic field line wander varies as a function of the amplitude of the plasma turbulence and the ratio of the thermal to magnetic pressure, known as the plasma beta.

scholarly journals Magnetic field line braiding in the solar atmosphere

2016 ◽  
Vol 12 (S327) ◽  
pp. 77-81
Author(s):  
S. Candelaresi ◽  
D. I. Pontin ◽  
G. Hornig
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Field Line ◽  
Solar Atmosphere ◽  
Magnetic Field Line ◽  
Solar Magnetic Field ◽  
Near Surface ◽  
Magnetic Field Topology ◽  
The Magnetic Field

AbstractUsing a magnetic carpet as model for the near surface solar magnetic field we study its effects on the propagation of energy injectected by photospheric footpoint motions. Such a magnetic carpet structure is topologically highly non-trivial and with its magnetic nulls exhibits qualitatively different behavior than simpler magnetic fields. We show that the presence of magnetic fields connecting back to the photosphere inhibits the propagation of energy into higher layers of the solar atmosphere, like the solar corona. By applying certain types of footpoint motions the magnetic field topology is is greatly reduced through magnetic field reconnection which facilitates the propagation of energy and disturbances from the photosphere.

Solitary Alfvén waveguide structures in a magnetized plasma

1980 ◽  
Vol 24 (1) ◽  
pp. 157-162 ◽  
Author(s):  
J. P. Sheerin ◽  
R. S. B. Ong
Keyword(s):  
Magnetic Field ◽  
Solitary Wave ◽  
Field Line ◽  
Magnetic Field Line ◽  
Axial Symmetry ◽  
Wave Structure ◽  
Magnetized Plasma ◽  
Alfven Wave ◽  
Wave Forms ◽  
The Magnetic Field

A nonlinear Alfvén wave structure with axial symmetry about the line of force of an ambient magnetic field is presented. The solitary wave forms a ‘ring’ shaped waveguide along the magnetic field line.

scholarly journals Delineating the magnetic field line escape pattern and stickiness in a poloidally diverted tokamak

2014 ◽  
Vol 21 (8) ◽  
pp. 082506 ◽  
Author(s):  
Caroline G. L. Martins ◽  
M. Roberto ◽  
I. L. Caldas
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
The Magnetic Field

Cyclotron Lines in the Spectra of Solar Flares and Solar Active Regions

1989 ◽  
Vol 104 (1) ◽  
pp. 449-456
Author(s):  
V. V. Zheleznyakov ◽  
E. Ya. Zlotnik
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Cross Section ◽  
Active Regions ◽  
Kinetic Temperature ◽  
Magnetic Tube ◽  
Tube Cross Section ◽  
Solar Active Regions ◽  
Electron Gyrofrequency ◽  
The Magnetic Field

AbstractIt was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 + 4) G along the magnetic tube axis. The linewidth Af/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 x 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.

scholarly journals Joint Discussion 3 Solar active regions and 3D magnetic structure

2006 ◽  
Vol 2 (14) ◽  
pp. 139-168
Author(s):  
Debi Prasad Choudhary ◽  
Michal Sobotka
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Large Scale ◽  
Focal Point ◽  
Active Regions ◽  
Theoretical Modelling ◽  
Solar Chromosphere ◽  
Origin And Evolution ◽  
Solar Active Regions ◽  
The Magnetic Field

AbstractKeeping in view of the modern powerful observing tools, among othersHinode(formerlySOLAR-B),STEREOand Frequency-Agile Solar Radiotelescope, and sophisticated modelling techniques, Joint Discussion 3 during the IAU General Assembly 2006 focused on the properties of magnetic field of solar active regions starting in deep interior of the Sun, from where they buoyantly rise to the coronal heights where the site of most explosive events are located. Intimately related with the active regions, the origin and evolution of the magnetic field of quiet Sun, the large scale chromospheric structures were also the focal point of the Joint Discussion. The theoretical modelling of the generation and dynamics of magnetic field in solar convective zone show that the interaction of the magnetic field with the Coriolis force and helical turbulent convection results in the tilts and twists in the emerging flux. In the photosphere, some of these fluxes appear in sunspots with field strengths up to about 6100 G. Spectro-polarimetric measurements reveal that the line of sight velocities and magnetic field of these locations are found to be uncombed and depend on depth in the atmosphere and exhibit gradients or discontinuities. The inclined magnetic fields beyond penumbra appear as moving magnetic features that do not rise above upper photospheric heights. As the flux rises, the solar chromosphere is the most immediate and intermediary layer where competitive magnetic forces begin to dominate their thermodynamic counterparts. The magnetic field at these heights is now measured using several diagnostic lines such as CaII854.2 nm, HI656.3 nm, and HeI1083.0 nm. The radio observations show that the coronal magnetic field of post flare loops are of the order of 30 G, which might represent the force-free magnetic state of active region in the corona. The temperatures at these coronal heights, derived from the line widths, are in the range from 2.4 to 3.7 million degree. The same line profile measurements indicate the existence of asymmetric flows in the corona. The theoretical extrapolation of photospheric field into coronal heights and their comparison with the observations show that there exists a complex topology with separatrices associated to coronal null points. The interaction of these structures often lead to flares and coronal mass ejections. The current MHD modelling of active region field shows that for coronal mass ejection both local active region magnetic field and global magnetic field due to the surrounding magnetic flux are important. Here, we present an extended summary of the papers presented in Joint Discussion 03 and open questions related to the solar magnetic field that are likely to be the prime issue with the modern observing facilities such asHinodeandSTEREOmissions.

Almost-invariant surfaces for magnetic field-line flows

1996 ◽  
Vol 56 (2) ◽  
pp. 361-382 ◽  
Author(s):  
S. R. Hudson ◽  
R. L. Dewar
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Gradient Flow ◽  
Invariant Surface ◽  
Infinite Dimensional ◽  
Invariant Surfaces ◽  
Magnetic Surfaces ◽  
Rotational Transform ◽  
The Magnetic Field

Two approaches to defining almost-invariant surfaces for magnetic fields with imperfect magnetic surfaces are compared. Both methods are based on treating magnetic field-line flow as a 1½-dimensional Hamiltonian (or Lagrangian) dynamical system. In thequadratic-flux minimizing surfaceapproach, the integral of the square of the action gradient over the toroidal and poloidal angles is minimized, while in theghost surfaceapproach a gradient flow between a minimax and an action-minimizing orbit is used. In both cases the almost-invariant surface is constructed as a family of periodic pseudo-orbits, and consequently it has a rational rotational transform. The construction of quadratic-flux minimizing surfaces is simple, and easily implemented using a new magnetic field-line tracing method. The construction of ghost surfaces requires the representation of a pseudo field line as an (in principle) infinite-dimensional vector and also is inherently slow for systems near integrability. As a test problem the magnetic field-line Hamiltonian is constructed analytically for a topologically toroidal, non-integrable ABC-flow model, and both types of almost-invariant surface are constructed numerically.

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