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

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>

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 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

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.

DIFFUSIVE TRANSPORT THROUGH A NONTWIST BARRIER IN TOKAMAKS

2007 ◽  
Vol 17 (05) ◽  
pp. 1589-1598 ◽  
Author(s):  
J. S. E. PORTELA ◽  
I. L. CALDAS ◽  
R. L. VIANA ◽  
P. J. MORRISON
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Magnetic Field Line ◽  
Present Model ◽  
Radial Diffusion ◽  
Diffusive Transport ◽  
Magnetic Shear ◽  
Transport Barrier ◽  
Line Structure ◽  
The Magnetic Field

The magnetic field line structure of tokamaks with reversed magnetic shear is analyzed by means of a nontwist map model that takes into account non-integrable perturbations that describe ergodic magnetic limiters. The map studied possess behavior expected of the standard nontwist map, a well-studied map, despite the different symmetries and the existence of coupled perturbations. A distinguising feature of nontwist maps is the presence of good surfaces in the reveresed shear region, and consequently the appearance of a transport barrier inside the plasma. Such barriers are observed in the present model and are seen to be very robust. Very strong perturbations are required to destroy them, and even after breaking, the transport turns out to be diffusive. Poloidal diffusion is found to be two orders of magnitude higher than radial diffusion.

Solar Dynamo

2020 ◽  
Author(s):  
Robert Cameron
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Large Scale ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Small Scale ◽  
The Sun ◽  
The Magnetic Field

The solar dynamo is the action of flows inside the Sun to maintain its magnetic field against Ohmic decay. On small scales the magnetic field is seen at the solar surface as a ubiquitous “salt-and-pepper” disorganized field that may be generated directly by the turbulent convection. On large scales, the magnetic field is remarkably organized, with an 11-year activity cycle. During each cycle the field emerging in each hemisphere has a specific East–West alignment (known as Hale’s law) that alternates from cycle to cycle, and a statistical tendency for a North-South alignment (Joy’s law). The polar fields reverse sign during the period of maximum activity of each cycle. The relevant flows for the large-scale dynamo are those of convection, the bulk rotation of the Sun, and motions driven by magnetic fields, as well as flows produced by the interaction of these. Particularly important are the Sun’s large-scale differential rotation (for example, the equator rotates faster than the poles), and small-scale helical motions resulting from the Coriolis force acting on convective motions or on the motions associated with buoyantly rising magnetic flux. These two types of motions result in a magnetic cycle. In one phase of the cycle, differential rotation winds up a poloidal magnetic field to produce a toroidal field. Subsequently, helical motions are thought to bend the toroidal field to create new poloidal magnetic flux that reverses and replaces the poloidal field that was present at the start of the cycle. It is now clear that both small- and large-scale dynamo action are in principle possible, and the challenge is to understand which combination of flows and driving mechanisms are responsible for the time-dependent magnetic fields seen on the Sun.

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