scholarly journals Propagation of a solitary wave along a magnetic field in a cold collision-free plasma

1961 ◽  
Vol 11 (1) ◽  
pp. 16-20 ◽  
Author(s):  
P. G. Saffman
Keyword(s):  
Magnetic Field ◽  
Geometric Mean ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Order Of Magnitude ◽  
Hydromagnetic Waves ◽  
Cold Collision ◽  
The Magnetic Field ◽  
Free Plasma ◽  
Alfven Velocity

It is shown that solitary hydromagnetic waves can propagate parallel to a uniform magnetic field in a cold collision-free plasma. These waves are exact solutions of the non-linear equations of motion except for the quasi-neutral approximation. The velocity of propagation lies in a range of values somewhat larger than the Alfvén velocity, and is of the order of 25 times the Alfvén velocity for hydrogen, the precise value depending upon the strength of the wave. Simple expressions exist for the velocities of the ions and electrons and the magnetic field inside the wave. The lines of force are spirals about the direction of propagation. The waves are symmetrical about their middle. The order of magnitude of their width is the geometric mean of the gyro-radii of the ions and electrons when moving with the Alfvén velocity. The maximum value of the magnetic field can be somewhat larger than the value away from the wave.

scholarly journals The structure of a hydromagnetic front in a cold collision-free plasma

1962 ◽  
Vol 12 (1) ◽  
pp. 81-87 ◽  
Author(s):  
P. G. Saffman
Keyword(s):  
Magnetic Field ◽  
Characteristic Frequency ◽  
Cold Plasma ◽  
Equations Of Motion ◽  
One Dimensional ◽  
Infinite Extent ◽  
Cold Collision ◽  
The Magnetic Field ◽  
Free Plasma ◽  
A Current

A one-dimensional steady solution of the equations of motion of a cold plasma in a magnetic field is obtained. The plasma is of semi-infinite extent, bounded by a plane interface which separates it from a vacuum or medium at rest. The particles approach from infinity, are reflected at the front, and return to infinity in the opposite direction. At infinity, the magnetic field is parallel and anti-parallel to the plasma streams, and is inclined at an angle to the normal to the interface. The front is a current sheet across which the lines of force are bent, with the component of the magnetic field in the plane of the front changing direction. The inertia of the electrons is neglected, and the characteristic frequency associated with the front is the ion gyro-frequency.

A study of the propagation of a solitary wave along the magnetic field in a cold collision-free plasma

2020 ◽  
Vol 27 (4) ◽  
pp. 042102
Author(s):  
Gohar Abbas ◽  
J. E. Allen ◽  
M. Coppins ◽  
L. Simons ◽  
L. James
Keyword(s):  
Magnetic Field ◽  
Solitary Wave ◽  
Cold Collision ◽  
The Magnetic Field ◽  
Free Plasma

scholarly journals The influence of resistivity gradients on shock conditions for a Petschek reconnection geometry

2016 ◽  
Vol 34 (4) ◽  
pp. 421-425
Author(s):  
Christian Nabert ◽  
Karl-Heinz Glassmeier
Keyword(s):  
Magnetic Field ◽  
Necessary Conditions ◽  
The Other ◽  
Diffusion Region ◽  
Two Dimensional ◽  
Characteristic Velocity ◽  
Magnetohydrodynamic Equations ◽  
One Dimensional ◽  
The Magnetic Field ◽  
Alfven Velocity

Abstract. Shock waves can strongly influence magnetic reconnection as seen by the slow shocks attached to the diffusion region in Petschek reconnection. We derive necessary conditions for such shocks in a nonuniform resistive magnetohydrodynamic plasma and discuss them with respect to the slow shocks in Petschek reconnection. Expressions for the spatial variation of the velocity and the magnetic field are derived by rearranging terms of the resistive magnetohydrodynamic equations without solving them. These expressions contain removable singularities if the flow velocity of the plasma equals a certain characteristic velocity depending on the other flow quantities. Such a singularity can be related to the strong spatial variations across a shock. In contrast to the analysis of Rankine–Hugoniot relations, the investigation of these singularities allows us to take the finite resistivity into account. Starting from considering perpendicular shocks in a simplified one-dimensional geometry to introduce the approach, shock conditions for a more general two-dimensional situation are derived. Then the latter relations are limited to an incompressible plasma to consider the subcritical slow shocks of Petschek reconnection. A gradient of the resistivity significantly modifies the characteristic velocity of wave propagation. The corresponding relations show that a gradient of the resistivity can lower the characteristic Alfvén velocity to an effective Alfvén velocity. This can strongly impact the conditions for shocks in a Petschek reconnection geometry.

Absorption of hydromagnetic waves in the ionosphere

1970 ◽  
Vol 48 (3) ◽  
pp. 362-366
Author(s):  
M. Abbas
Keyword(s):  
Magnetic Field ◽  
Frequency Range ◽  
Parallel Propagation ◽  
Hydromagnetic Waves ◽  
The Magnetic Field

Absorption of hydromagnetic waves in the ionosphere propagated normal to the magnetic field is calculated at various frequencies and compared with the absorption for parallel propagation. Data corresponding to both daytime and nighttime ionospheres are used. Waves propagated normal to the magnetic field are highly absorbed through the daytime ionosphere at frequencies above a few Hz; the nighttime ionosphere, however, is virtually transparent to waves in the frequency range of 10−3 to 20 Hz. A comparison of the absorption processes for waves propagated parallel and normal to the magnetic field is made.

Influence of the magnetic field of stellar wind on hot jupiter’s envelopes

2019 ◽  
Vol 15 (S354) ◽  
pp. 268-279
Author(s):  
Dmitry V. Bisikalo ◽  
Andrey G. Zhilkin
Keyword(s):  
Magnetic Field ◽  
Plasma Flow ◽  
Coronal Mass Ejections ◽  
Stellar Wind ◽  
Roche Lobe ◽  
Bow Shock ◽  
Hot Jupiters ◽  
The Magnetic Field ◽  
Alfven Velocity ◽  
Hot Jupiter

AbstractHot Jupiters have extended gaseous (ionospheric) envelopes, which extend far beyond the Roche lobe. The envelopes are loosely bound to the planet and, therefore, are strongly influenced by fluctuations of the stellar wind. We show that, since hot Jupiters are close to the parent stars, magnetic field of the stellar wind is an important factor defining the structure of their magnetospheres. For a typical hot Jupiter, velocity of the stellar wind plasma flow around the atmosphere is close to the Alfvén velocity. As a result stellar wind fluctuations, such as coronal mass ejections, can affect the conditions for the formation of a bow shock around a hot Jupiter. This effect can affect observational manifestations of hot Jupiters.

A Discussion on the early days of ionospheric research and the theory of electric and magnetic waves in the ionosphere and magnetosphere - Electromagnetic and hydromagnetic waves in a cold magnetoplasma

1975 ◽  
Vol 280 (1293) ◽  
pp. 57-93 ◽  
Keyword(s):  
Magnetic Field ◽  
Group Velocity ◽  
Plasma Frequency ◽  
Geometric Mean ◽  
Wave Frequency ◽  
Beam Direction ◽  
Rich Variety ◽  
Infinite Conductivity ◽  
The Rich ◽  
Hydromagnetic Waves

The basis of the theory of waves in a cold homogeneous magnetoplasma is reviewed. The radio approximation (associated with Appleton) applies when the wave-frequency is large compared with the geometric mean of the electronic and ionic gyrofrequencies. The hydromagnetic approximation (associated with Alfven) corresponds to infinite conductivity along the lines of flux of the imposed magnetic field and applies when the wave-frequency is small compared with the plasma-frequency. The rich variety of dispersion phenomena existing in a magnetoplasma is illustrated by polar diagrams showing both the variation of group-velocity with beam-direction and the direction in which the antenna must be pointed to aim a beam in a particular direction.

Magnetohydrodynamic Stability of Two Streaming Superposed Viscoelastic Conducting Fluids

2001 ◽  
Vol 56 (6-7) ◽  
pp. 416-439
Author(s):  
Mohamed Fahmy El
Keyword(s):  
Magnetic Field ◽  
Stable Configuration ◽  
Retardation Time ◽  
Horizontal Magnetic Field ◽  
Fluid Velocities ◽  
Unstable Configuration ◽  
The Stability ◽  
The Magnetic Field ◽  
Conducting Fluids ◽  
Alfven Velocity

Abstract The stability of the plane interface separating two Oldroydian viscoelastic superposed moving fluids of uniform densities when immersed in a uniform horizontal magnetic field has been in­ vestigated. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities. It is found that the potentially stable configuration remains stable if the fluids are at rest, while it becomes unstable if the fluids move. The stability criterion is found to be independent of the viscosity and viscoelasticity, and to be dependent on the orientation of the magnetic field and the magnitudes of the fluids and Alfven velocities. It is also found that the potentially unstable configuration remains unstable in the absence of average fluid velocities, or in the presence of fluid velocities and absence of a magnetic field. The magnetic field is found to stabilize a certain wavenumbers range of the unstable configuration even in the presence of the effects of viscoelasticity. The behaviour of growth rates with respect to the stress relaxation time, strain retardation time, fluid and Alfven velocity parameters is examined analytically, and the stability conditions are obtained and discussed. -Pacs: 47.20.-k; 47.50.+d; 47.65.+a.

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