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).

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 Plasma Flow and Solar Wind Acceleration in Non-Radial Coronal Magnetic Fields

1983 ◽  
Vol 102 ◽  
pp. 473-477
Author(s):  
H. Biernat ◽  
N. Kömle ◽  
H. Rucker
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Plasma Flow ◽  
Coronal Holes ◽  
Expansion Velocity ◽  
The Sun ◽  
Solar Wind Acceleration ◽  
Coronal Magnetic Fields ◽  
Field Lines ◽  
The Magnetic Field

In the vicinity of the Sun — especially above coronal holes — the magnetic field lines show strong non-radial divergence and considerable curvature (see e.g. Kopp and Holzer, 1976; Munro and Jackson, 1977; Ripken, 1977). In the following we study the influence of these characteristics on the expansion velocity of the solar wind.

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.

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 Summary of Conference

1985 ◽  
Vol 107 ◽  
pp. 529-536
Author(s):  
Vytenis M. Vasyliunas
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Magnetic Reconnection ◽  
Field Line ◽  
Magnetic Field Line ◽  
Plasma Flow ◽  
Remarkable Degree ◽  
Ideal Mhd ◽  
Points Of View ◽  
The Magnetic Field

For a meeting of people from such widely different fields, this Symposium has exhibited a remarkable degree of unity. There has been one key concept running as a thread throughout the Symposium: the concept of magnetic field line reconnection, or magnetic field line merging as I prefer to call it. It was dealt with directly in many papers, and many others dealt indirectly with it and various related aspects. The concept was applied in the Symposium to an amazing variety of objects and was examined from many points of view and by many different techniques. Magnetic field line reconnection or merging is a paradoxical concept. It clearly depends upon magnetohydrodynamics (MHD); for example, constraints imposed by the MHD relation between the magnetic field and the plasma flow are essential to set it up - without these constraints (if, for example, the electric field parallel to the magnetic field could assume any desired value) the problems we discuss under the heading of magnetic reconnection would merely be moderately complicated problems of magnetostatics. At the same time, departures from ideal MHD are also an essential and unavoidable part of the concept.

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 Electron dynamics during substorm dipolarization in Mercury's magnetosphere

2005 ◽  
Vol 23 (10) ◽  
pp. 3389-3398 ◽  
Author(s):  
D. C. Delcourt ◽  
K. Seki ◽  
N. Terada ◽  
Y. Miyoshi
Keyword(s):  
Magnetic Field ◽  
High Energy ◽  
Expansion Phase ◽  
Earth’S Magnetosphere ◽  
High Energy Electrons ◽  
Earth's Magnetosphere ◽  
Magnetic Field Model ◽  
Particle Simulations ◽  
Field Lines ◽  
The Magnetic Field

Abstract. We examine the nonlinear dynamics of electrons during the expansion phase of substorms at Mercury using test particle simulations. A simple model of magnetic field line dipolarization is designed by rescaling a magnetic field model of the Earth's magnetosphere. The results of the simulations demonstrate that electrons may be subjected to significant energization on the time scale (several seconds) of the magnetic field reconfiguration. In a similar manner to ions in the near-Earth's magnetosphere, it is shown that low-energy (up to several tens of eV) electrons may not conserve the second adiabatic invariant during dipolarization, which leads to clusters of bouncing particles in the innermost magnetotail. On the other hand, it is found that, because of the stretching of the magnetic field lines, high-energy electrons (several keVs and above) do not behave adiabatically and possibly experience meandering (Speiser-type) motion around the midplane. We show that dipolarization of the magnetic field lines may be responsible for significant, though transient, (a few seconds) precipitation of energetic (several keVs) electrons onto the planet's surface. Prominent injections of energetic trapped electrons toward the planet are also obtained as a result of dipolarization. These injections, however, do not exhibit short-lived temporal modulations, as observed by Mariner-10, which thus appear to follow from a different mechanism than a simple convection surge.

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.

scholarly journals Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

2013 ◽  
Vol 8 (S300) ◽  
pp. 416-417
Author(s):  
G. Allen Gary ◽  
Qiang Hu ◽  
Jong Kwan Lee
Keyword(s):  
Magnetic Field ◽  
Coronal Loop ◽  
Field Model ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Magnetic Field Model ◽  
Free Parameters ◽  
Field Lines ◽  
Fitness Parameter ◽  
The Magnetic Field

AbstractThis article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

Ganymede’s magnetic footprint mapping: Modeling and HST observations

2020 ◽  
Author(s):  
Tatphicha Promfu ◽  
Suwicha Wannawichian ◽  
Jonathan Nichols ◽  
John Clarke
Keyword(s):  
Magnetic Field ◽  
Hubble Space Telescope ◽  
Volcanic Eruptions ◽  
Plasma Pressure ◽  
Magnetic Field Mapping ◽  
Hot Plasma ◽  
Pressure Anisotropy ◽  
Magnetic Field Model ◽  
Field Lines ◽  
The Magnetic Field

<p>In this work, the locations of observed Ganymede’s magnetic footprint were compared with the locations predicted by the magnetic field model under different plasma conditions. The shifts of Ganymede's magnetic footprint locations from average footpath given by Grodent et al. (2008) were analyzed. The average path is created from about 1000 images taken by instruments onboarded Hubble Space Telescope (HST). The position shifts indicate the variation of magnetic field line mapping from Ganymede to Jupiter’s ionosphere. The two sets of data from HST were analyzed to obtain the locations of Ganymede’s magnetic footprint in 2007 and 2016. For both sets of data, at longitude ranging approximately from 170° to 180°, we found that the locations were significantly shifted in poleward direction between 0.5° to 2° from the average footpath. Different from data in May 2007, the Ganymede’s magnetic footprint locations in May 2016 at longitude about 160° could possibly locate in equatorward direction. At orbital distance of Ganymede about 15 R<sub>J</sub>, in Jupiter’s middle magnetosphere, there is strong influence of plasma, whose major source is Io’s volcanic eruptions. Thus, the variations of plasma resulting in the stretching of magnetic field lines affect the magnetic field mapping from Ganymede to ionosphere. Furthermore, based on the magnetodisc model, the hot plasma pressure anisotropy strongly influences the stretching of the field lines and the mapped locations of Ganymede’s footprint in ionosphere to be shifted in either poleward or equatorward directions. In this study, we detected both poleward and equatorward shifts in different observations, whose connection with the plasma environment in the middle magnetosphere awaits for further study.</p>

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