Summary of Conference

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.

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Possible Generation Mechanism for Alfvenic Velocity Spikes and Magnetic Field Switchbacks as Observed by PSP

10.5194/egusphere-egu2020-18832 ◽

2020 ◽

Author(s):

Xingyu Zhu ◽

Jiansen He ◽

Die Duan ◽

Lei Zhang ◽

Liping Yang ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Reconnection ◽

Field Line ◽

Magnetic Field Line ◽

Small Scale ◽

The Sun ◽

Internal Temperature ◽

External Temperature ◽

Pulse Type ◽

The Magnetic Field

<div>According to Parker's theory in the 1950s, the magnetic lines of force extending from the sun to the interplanetary appear to be Archimedean spirals. From 1960 to 1970, it was found that the interplanetary magnetic field not only follows the Archimedes spiral structure, but also has the characteristics of Alfvenic turbulence. How do these Alfvenic turbulence occur? What will be the characteristics when getting close to the Sun? Parker Solar Probe at 0.17au has found that there are often intermittent Alfvenic pulses (or called Alfvenic velocity spikes) in the solar wind. These pulses are high enough that the disturbed magnetic lines may even turn back. What's more interesting is that there is always a compressibility disturbance along with the Alfven pulse: the temperature and density inside and outside the Alfven pulse are different, the internal temperature is often higher than the external temperature, some of the internal density is higher than the external and some is lower than the external. The Alfven pulse often shows asymmetry on both sides: the magnetic field and velocity on one side are "clean" jumps, while on the other side are multiple small-scale disturbances of variables in the transition boundary layer. In view of this new phenomenon of magnetic field line switch back with compressed Alfven pulse, how it is generated is raising a hot debate. It is thought that the exchange magnetic reconnection of the solar atmosphere may be the underlying physical mechanism. But in the traditional exchange magnetic reconnection image, after reconnection, the zigzag magnetic field line can easily become smooth, which can not maintain the distortion of the magnetic field line, and may not be able to explain the observed Alfven pulses. In this work, we propose a new model called "Excitation of Alfven Pulses by Continuous Intermittent Interchange Reconnection with Guide Field Discontinuity" (EAP-CIIR-GFD). By analyzing and comparing the simulation results and observation results, we find that the model can explain the following observation features: (1) Alfven disturbance is pulse type and asymmetric; (2) Alfven pulse is compressible with the enhancement of internal temperature and the increase or decrease of the internal density; (3) Alfven pulse can cause serious distortion of the magnetic field line. Improvements to the model will also be discussed in the report.</div>

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Study on the Effect of Magnetic Field on Temperature Domain During Electrolytic Processing

10.21203/rs.3.rs-764735/v1 ◽

2021 ◽

Author(s):

Jianli Jia ◽

Mingzhe Wang ◽

Tianci Xu ◽

Haotian Pangyan ◽

Xueying Zhou

Keyword(s):

Magnetic Field ◽

Flow Field ◽

Electric Field ◽

Field Line ◽

Magnetic Field Line ◽

Current Density ◽

Design Methods ◽

Electrolyte Temperature ◽

Electrolyte Flow ◽

The Magnetic Field

Abstract A physical model, mathematical model and geometric model of multi-physical field (electric field, flow field, temperature field, magnetic field) were established to explore the influence of magnetic field on the temperature domain in the gap during ECM. The change law of temperature domain of ECM gap under different magnetic field design methods was studied by using COMSOL MULTIPHYSICS. The scheme is as follows: the magnetic field line is perpendicular to the electric field and the flow field is parallel; the magnetic field line is parallel to the electric field and the flow field is vertical; the electric field of the magnetic field is vertical and the flow field is vertical. The change law of the influence of the magnetic field on the electrolyte temperature is studied by simulation. The changes of current density under three magnetic field design methods and different electrolyte flow were studied. The simulation results show that when the magnetic field is perpendicular to the electric field and the flow field, the temperature change is relatively gentle, and the flow field changes uniformly under the action of the magnetic field volume force, so that the change of current density is relatively stable; The current density of anodic dissolution increases with the increase of voltage, resulting in the increase of electrolyte temperature and heat, further reducing the gap and machining gap, and the temperature in the gap will be greatly increased. Under the action of magnetic field, the electrolyte flow rate increases and the electrolyte temperature decreases greatly.

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

Annales Geophysicae ◽

10.1007/s00585-000-1257-6 ◽

2000 ◽

Vol 18 (10) ◽

pp. 1257-1262 ◽

Cited By ~ 1

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)

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The development of magnetic field line wander by plasma turbulence

Journal of Plasma Physics ◽

10.1017/s0022377817000617 ◽

2017 ◽

Vol 83 (4) ◽

Cited By ~ 5

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.

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Mapping of steady-state electric fields and convective drifts in geomagnetic fields – Part 1: Elementary models

Annales Geophysicae ◽

10.5194/angeo-34-55-2016 ◽

2016 ◽

Vol 34 (1) ◽

pp. 55-65 ◽

Cited By ~ 4

Author(s):

A. D. M. Walker ◽

G. J. Sofko

Keyword(s):

Magnetic Field ◽

Steady State ◽

Electric Field ◽

Electric Fields ◽

Magnetic Field Line ◽

Geomagnetic Field ◽

Geomagnetic Field Models ◽

Spatial Derivatives ◽

Field Lines ◽

The Magnetic Field

Abstract. When studying magnetospheric convection, it is often necessary to map the steady-state electric field, measured at some point on a magnetic field line, to a magnetically conjugate point in the other hemisphere, or the equatorial plane, or at the position of a satellite. Such mapping is relatively easy in a dipole field although the appropriate formulae are not easily accessible. They are derived and reviewed here with some examples. It is not possible to derive such formulae in more realistic geomagnetic field models. A new method is described in this paper for accurate mapping of electric fields along field lines, which can be used for any field model in which the magnetic field and its spatial derivatives can be computed. From the spatial derivatives of the magnetic field three first order differential equations are derived for the components of the normalized element of separation of two closely spaced field lines. These can be integrated along with the magnetic field tracing equations and Faraday's law used to obtain the electric field as a function of distance measured along the magnetic field line. The method is tested in a simple model consisting of a dipole field plus a magnetotail model. The method is shown to be accurate, convenient, and suitable for use with more realistic geomagnetic field models.

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Magnetic field line braiding in the solar atmosphere

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317001818 ◽

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.

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

Annales Geophysicae ◽

10.5194/angeo-24-339-2006 ◽

2006 ◽

Vol 24 (1) ◽

pp. 339-354 ◽

Cited By ~ 9

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).

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Solitary Alfvén waveguide structures in a magnetized plasma

Journal of Plasma Physics ◽

10.1017/s0022377800022698 ◽

1980 ◽

Vol 24 (1) ◽

pp. 157-162 ◽

Cited By ~ 7

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.

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