scholarly journals Quantitative estimations of the anomalous plasma diffusion in an active region

1968 ◽  
Vol 35 ◽  
pp. 131-133
Author(s):  
M. Kopecký ◽  
G. V. Kuklin
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Field Line ◽  
Solar Atmosphere ◽  
Plasma Diffusion ◽  
Field Lines ◽  
The Magnetic Field

In some recent papers the interdependence of the gas and magnetic-field motions in the solar atmosphere was considered. Some results indicate the occurrence of gas motion along the magnetic-field lines combined with motion of the field line, but sometimes we have to assume an obvious gas motion across the magnetic-field lines. As one of the possible mechanisms explaining this fact the anomalous plasma diffusion may be proposed.

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 Polarization and Position Measurements of Type III Bursts

1980 ◽  
Vol 86 ◽  
pp. 315-322 ◽  
Author(s):  
S. Suzuki ◽  
G.A. Dulk ◽  
K. V. Sheridan
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Open Field ◽  
Langmuir Waves ◽  
Type Iii ◽  
Brightness Temperatures ◽  
Polarization Characteristics ◽  
Field Lines ◽  
Cosine Law ◽  
The Magnetic Field

We report on the positional and polarization characteristics of Type III bursts in the range 24–220 MHz as measured by the Culgoora radioheliograph, spectrograph and spectropolarimeter. Our study includes 997 bursts which are of two classes: fundamental-harmonic (F-H) pairs and “structureless” bursts with no visible F-H structure. In a paper published elsewhere (Dulk and Suzuki, 1979) we give a detailed description and include observations of source sizes, heights and brightness temperatures. Here we concentrate on the polarization of the bursts and the variation of polarization from centre to limb. The observed centre-to-limb decrease in polarization approximately follows a cosine law. This decrease is not as predicted by simple theory but is consistent with other observations which imply that open field lines from an active region diverge strongly. The observed o-mode polarization of harmonic radiation implies that the wave vectors of Langmuir waves are always parallel, within about 20°, to the magnetic field, while the constancy of H polarization with frequency implies that the ratio fB/fP, the Alfvén speed vA and the plasma beta are constant with height on the open field lines above an active region. Finally, we infer that some factor, in addition to the magnetic field strength, controls the polarization of F radiation.

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.

scholarly journals Rotation of the magnetic field in Earth's magnetosheath by bulk magnetosheath plasma flow

2006 ◽  
Vol 24 (1) ◽  
pp. 339-354 ◽  
Author(s):  
M. Longmore ◽  
S. J. Schwartz ◽  
E. A. Lucek
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Plasma Flow ◽  
Mean Value ◽  
Flow Coupling ◽  
Parker Spiral ◽  
Magnetic Field Model ◽  
Field Lines ◽  
The Magnetic Field

Abstract. Orientations of the observed magnetic field in Earth's dayside magnetosheath are compared with the predicted field line-draping pattern from the Kobel and Flückiger static magnetic field model. A rotation of the overall magnetosheath draping pattern with respect to the model prediction is observed. For an earthward Parker spiral, the sense of the rotation is typically clockwise for northward IMF and anticlockwise for southward IMF. The rotation is consistent with an interpretation which considers the twisting of the magnetic field lines by the bulk plasma flow in the magnetosheath. Histogram distributions describing the differences between the observed and model magnetic field clock angles in the magnetosheath confirm the existence and sense of the rotation. A statistically significant mean value of the IMF rotation in the range 5°-30° is observed in all regions of the magnetosheath, for all IMF directions, although the associated standard deviation implies large uncertainty in the determination of an accurate value for the rotation. We discuss the role of field-flow coupling effects and dayside merging on field line draping in the magnetosheath in view of the evidence presented here and that which has previously been reported by Kaymaz et al. (1992).

Coherent Curvature Emission in Pulsar Magnetospheres: Non-dipolar Geometric Effects

1993 ◽  
Vol 10 (3) ◽  
pp. 258-262 ◽  
Author(s):  
Qinghuan Luo
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Rotation Period ◽  
Lorentz Factor ◽  
Maser Emission ◽  
Specific Geometry ◽  
Field Lines ◽  
First Time ◽  
The Magnetic Field ◽  
Geometric Effects

AbstractThe effects of the specific geometry of the magnetic field (such as field lines with torsion) on curvature emission and absorption in pulsar magnetospheres are discussed. Curvature maser emission can arise from two effects: the curvature drift, as has already been discussed in the literature, and field line torsion as discussed here in detail for the first time. Maser emission due to field line torsion can operate only when the Lorentz factor is larger than a certain value. However, when the Lorentz factor of electrons or positrons is sufficiently high, curvature masering is due to both curvature drift and magnetic field line torsion. The optical depth in the case of field line torsion is estimated. It is shown that if torsion is due to rotation, the resultant luminosity should be dependent on the rotation period in such a way that shorter periods correspond to larger luminosities.

scholarly journals Large polar caps for twisted magnetosphere of magnetars

2019 ◽  
Author(s):  
H Tong
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Energy Release ◽  
Open Field ◽  
Magnetic Energy ◽  
Hot Spot ◽  
Open Field Line ◽  
Field Lines ◽  
The Magnetic Field ◽  
Magnetic Energy Release

Abstract The magnetic field of magnetars may be twisted compared with that of normal pulsars. Previous works mainly discussed magnetic energy release in the closed field line regions of magnetars. For a twisted magnetic field, the field lines will inflate in the radial direction. Similar to normal pulsars, the idea of light cylinder radius is introduced. More field lines will cross the light cylinder and become open for a twisted magnetic field. Therefore, magnetars may have a large polar cap, which may correspond to the hot spot during outburst. Particle flow in the open field line regions will result in the untwisting of the magnetic field. Magnetic energy release in the open field line regions can be calculated. The model calculations can catch the general trend of magnetar outburst: decreasing X-ray luminosity, shrinking hot spot etc. For magnetic energy release in the open field line regions, the geometry will be the same for different outburst in one magnetar.

scholarly journals Magnetic Configuration and Evolution in a Solar Active Region

2001 ◽  
Vol 203 ◽  
pp. 294-296
Author(s):  
Y. Liu ◽  
H. Zhang
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Reconnection ◽  
Solar Atmosphere ◽  
Solar Active Region ◽  
Magnetic Configuration ◽  
Magnetic Helicity ◽  
Space Satellite ◽  
The Magnetic Field

We present results of the analysis of NOAA 8668, which was observed successively by space satellite (SOHO) and ground-based observatories (BBSO, Huairou). The combined observation offers us a good example of a region observed from low to high solar atmosphere. Several flares and a sigmoid filament were observed in the AR, and we observed the sigmoid filament from its birth to disintegration. The configuration of the magnetic field of the AR changed quickly as well as the loops. From EIT movies, we can even judge the sign of the sigmoid filament's magnetic helicity. The forming and heating of the loops were the result of magnetic reconnection, and the corona seemed heated when the loops became opened.

scholarly journals A comparison between FUV remote sensing of magnetotail stretching and the T01 model during quiet conditions and growth phases

2007 ◽  
Vol 25 (1) ◽  
pp. 161-170 ◽  
Author(s):  
C. Blockx ◽  
J.-C. Gérard ◽  
V. Coumans ◽  
B. Hubert ◽  
M. Meurant
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Field Line ◽  
Time History ◽  
Field Configuration ◽  
Growth Phases ◽  
Theoretical Position ◽  
Proton Precipitation ◽  
Field Lines ◽  
The Magnetic Field

Abstract. In a previous study, Blockx et al. (2005) showed that the SI12 camera on board the IMAGE spacecraft is an excellent tool to remotely determine the position of the isotropy boundary (IB) in the ionosphere, and thus is able to provide a reasonable estimate of the amount of stretching of the magnetic field lines in the magetotail. By combining an empirical model of the magnetospheric configuration with Sergeev's criterion for non-adiabatic motion, it is also possible to obtain a theoretical position of IB in the ionosphere, for known conditions in the solar wind. Earlier studies have demonstrated the inadequacy of the Tsyganenko-1989 (T89) model to quantitatively reproduce the field line stretching, particularly during growth phases. In this study, we reexamine this question using the T01 model which considers the time history of the solar wind parameters. We compare the latitude of IB derived from SI12 global images near local midnight with that calculated from the T01 model and the Sergeev's criterion. Observational and theoretical results are found to frequently disagree. We use in situ measurements of the magnetic field with the GOES-8 satellite to discriminate which of the two components in the calculation of the theoretical position of the IB (the T01 model or Sergeev's criterion) induces the discrepancy. For very quiet magnetic conditions, we find that statistically the T01 model approximately predicts the correct location of the maximum proton precipitation. However, large discrepancies are observed in individual cases, as demonstrated by the large scatter of predicted latitudes. For larger values of the AE index, the model fails to predict the observed latitude of the maximum proton intensity, as a consequence of the lack of consideration of the cross-tail current component which produces a more elongated field configuration at the location of the proton injection along the field lines. We show that it is possible to match the observed location of the maximum proton precipitation by decreasing the current sheet half-thickness D parameter. We thus conclude that underestimation of the field line stretching leads to inadequately prediction of the boundary latitude of the non-adiabatic proton precipitation region.

Resistively induced plasma diffusion due to the trivial marginal modes of ideal MHD

1988 ◽  
Vol 39 (1) ◽  
pp. 157-168
Author(s):  
W. Liebert ◽  
E. Rebhan
Keyword(s):  
Magnetic Field ◽  
Heat Conduction ◽  
Perturbation Analysis ◽  
Cross Diffusion ◽  
Magnetic Surfaces ◽  
Ideal Mhd ◽  
Reductive Perturbation ◽  
Plasma Diffusion ◽  
Field Lines ◽  
The Magnetic Field

The influence of nonlinearities and plasma resistivity on the so-called trivial marginal modes of ideal MHD is investigated. It turns out that to lowest significant order of a reductive perturbation analysis nonlinearities have no influence, while in toroidal confinement configurations resistivity induces a local plasma diffusion across the magnetic surfaces. This is demonstrated for tokamaks with zero poloidal current density. In addition, the appearance of singularities in the plasma motion parallel to the magnetic field lines suggests a profile condition at the edge of the plasma. Heat conduction would directly tend to keep these effects at lower level, while indirectly it creates a reinforcement mechanism through the coupling to usual cross diffusion.

Geometry of magnetic field lines approaching a current sheet

2003 ◽  
Vol 69 (6) ◽  
pp. 541-550
Author(s):  
MANUEL NÚÑEZ
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Two Dimensions ◽  
Time Of Arrival ◽  
Positive Contribution ◽  
Neutral Sheet ◽  
Spatial Function ◽  
Field Lines ◽  
The Magnetic Field ◽  
A Current

The evolution of a magnetic field line in two dimensions near a neutral sheet is analysed. It is found that the general features of this evolution are rather independent of any particular model, provided that the magnetic field is small and the current density does not vanish. The time of arrival of a field line to the neutral sheet as well as its breaking and reconnection are proved to be finite and to satisfy a simple formula whose main parameter is the resistivity, which may be a spatial function. The shape of the evolving field lines satisfies a differential equation whose solution in some simple cases is shown to agree with certain classical reconnection configurations. Hyperresistivity is found to be more often a hindrance than a positive contribution to the reconnection process.

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