scholarly journals Viscoelastic type magnetic effects and self-gravity on the propagation of MHD waves

Meccanica ◽  
2020 ◽  
Vol 55 (11) ◽  
pp. 2199-2214
Author(s):  
Franca Franchi ◽  
Barbara Lazzari ◽  
Roberta Nibbi
Keyword(s):  
Alfven Waves ◽  
Accelerated Expansion ◽  
Mhd Waves ◽  
Critical Threshold ◽  
Alfvén Waves ◽  
Sonic Waves ◽  
The Stability ◽  
Definition Of ◽  
Self Gravity ◽  
Network Patterns

Abstract We take up the challenge to explain the correlation between the Jeans instability topic towards star formation within the accelerated expansion of universe and the role of torsional shear-like Alfven waves in triggering the formation of network patterns, by proposing new mathematical models for self-gravitating interstellar non ideal MHD plasmas. The diffusion of the gravitational field is included via a parabolic Einstein’s equation with the cosmological constant, whereas anomalous resistive features are described through non ideal Ohm’s laws incorporating inertia terms, to account of relaxation and retardation magnetic responses. We perform a spectral analysis to test the stability properties of the novel constitutive settings where dissipative and elastic devices act together, by emphasizing the differences with previous models. As a main result, we highlight the definition of a lower critical threshold, here called the Jeans-Einstein wavenumber, against collapse formation towards the formation of longitudinal gravito-magneto-sonic waves and transverse non gravitational Alfven waves exhibiting larger effective wavespeeds, due to the hyperbolic-parabolic diffusion of the magnetic field. Consequently shorter collisional times are allowable so, beyond the plasma-beta, another interesting key point is the definition of the Ohm number to revisit the timescale topic, towards reviewed Reynolds and Lundquist numbers able to better capture the microphysical phenomena of Magnetic Reconnection in narrow diffusion regimes.

scholarly journals Relativistic Alfvén Waves on the jet of BL Lacertae

2014 ◽  
Vol 10 (S313) ◽  
pp. 147-152
Author(s):  
Marshall H. Cohen ◽  
David L. Meier
Keyword(s):  
Magnetic Field ◽  
Pitch Angle ◽  
Lorentz Factor ◽  
Alfven Waves ◽  
Longitudinal Component ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Bl Lacertae ◽  
Pattern Speeds ◽  
Helical Magnetic Field

AbstractThe jet of BL Lac displays transverse patterns that propagate downstream superluminally. We suggest that they are transverse Alfvén waves propagating on the longitudinal component of a helical magnetic field. The speed of the wave adds relativistically to the speed of the beam, and the apparent speed of the pattern is greater than the beam speed. Models for the jet and the MHD waves give values for the Lorentz factor of the beam of 3–4.4 and pitch angle of the helical magnetic field of 43° - 65°. These are consistent with other estimates, if the beam and pattern speeds are allowed to differ.

The Stability of the Relativistic Alfvén Waves

1983 ◽  
Vol 23 (2) ◽  
pp. 117-132
Author(s):  
C. D. Ciubotariu ◽  
D. I. Zoler ◽  
N. S. Thirer
Keyword(s):  
Alfven Waves ◽  
Alfvén Waves ◽  
The Stability

Three-dimensional stability of solitary shear kinetic Alfvén waves in a low-beta plasma

1989 ◽  
Vol 41 (1) ◽  
pp. 171-184 ◽  
Author(s):  
K. P. Das ◽  
L. P. J. Kamp ◽  
F. W. Sluijter
Keyword(s):  
Growth Rate ◽  
Dimensional Stability ◽  
Three Dimensional ◽  
Alfven Waves ◽  
Magnetized Plasma ◽  
Alfvén Waves ◽  
Ion Acoustic Solitons ◽  
The Stability ◽  
External Uniform Magnetic Field ◽  
Kinetic Alfvén Waves

The three-dimensional stability of solitary shear kinetic Alfvén waves in a low-β plasma is investigated by the method of Zakharov & Rubenchik (1974). It is found that there is no instability if the direction of perturbation falls within a certain region of space. The growth rate of the instability for the unstable region is determined. This growth rate is found to decrease with increasing angle between the direction of propagation of the solitary wave and the direction of the external uniform magnetic field. A particular case of the present analysis gives results on the stability of ion-acoustic solitons in a magnetized plasma.

Stability of Alfvén wings in uniform plasmas

2007 ◽  
Vol 73 (6) ◽  
pp. 957-966
Author(s):  
P. A. SALLAGO ◽  
A. M. PLATZECK
Keyword(s):  
Solar System ◽  
Normal Modes ◽  
Background Field ◽  
Alfven Waves ◽  
Magnetized Plasma ◽  
Alfvén Waves ◽  
Solar System Bodies ◽  
Uniform Background ◽  
The Stability ◽  
Magnetohydrodynamic System

AbstractA conducting source moving uniformly through a magnetized plasma generates, among a variety of perturbations, Alfvén waves. An interesting characteristic of Alfvén waves is that they can build up structures in the plasma called Alfvén wings. These wings have been detected and measured in many solar system bodies, and their existence has also been theoretically proven. However, their stability remains to be studied. The aim of this paper is to analyze the stability of an Alfvén wing developed in a uniform background field, in the presence of an incompressible perturbation that has the same symmetry as the Alfvén wing, in the magnetohydrodynamic approximation. The study of the stability of a magnetohydrodynamic system is often performed by linearizing the equations and using either the normal modes method or the energy method. In spite of being applicable for many problems, both methods become algebraically complicated if the structure under analysis is a highly non-uniform one. Palumbo has developed an analytical method for the study of the stability of static structures with a symmetry in magnetized plasmas, in the presence of incompressible perturbations with the same symmetry as the structure (Palumbo 1998 Thesis, Universidad de Firenze, Italia). In the present paper we extend this method for Alfvén wings that are stationary structures, and conclude that in the presence of this kind of perturbation they are stable.

The influence of negatively charged heavy ions on Alfven waves in a cometary environment

2014 ◽  
Vol 4 (3) ◽  
pp. 643-654
Author(s):  
Venugopal Chandu ◽  
Sreekala G ◽  
Sijo Sebastian ◽  
Manesh Michael ◽  
Neethu Theresa Willington ◽  
...  
Keyword(s):  
Heavy Ions ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Loss Cone ◽  
Direction Parallel ◽  
Oxygen Ions ◽  
Oxygen Ion ◽  
Laboratory Plasmas ◽  
Cone Type ◽  
The Stability

Alfven waves are important in a wide variety of areas like astrophysical, space and laboratory plasmas. In cometary environments, waves in the hydromagnetic range of frequencies are excited predominantly by heavy ions. We, therefore, study the stability of Alfven waves in a plasma of hydrogen ions, positively and negatively charged oxygen ions and electrons. Each species has been modeled by drifting distributions in the direction parallel to the magnetic field; in the perpendicular direction the distribution is  simulated with a loss cone type distribution obtained through the subtraction of two Maxwellian distributions with different temperatures.  We find that for frequencies  ( and   being respectively the Doppler shifted and hydrogen ion gyro-frequencies ), the peak growth  rate  increases with increasing negatively charged oxygen ion densities. On the other hand, for frequencies   (being the oxygen ion gyro-frequencies) the region of wave growth increases with increasing negatively charged oxygen ion densities.

scholarly journals Contribution of observed multi frequency spectrum of Alfvén waves to coronal heating

2019 ◽  
Vol 623 ◽  
pp. A37 ◽  
Author(s):  
P. Pagano ◽  
I. De Moortel
Keyword(s):  
Active Region ◽  
Power Spectrum ◽  
Solar Corona ◽  
Coronal Loop ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Coronal Loops ◽  
Phase Mixing ◽  
Transverse Oscillations

Context. Whilst there are observational indications that transverse magnetohydrodynamic (MHD) waves carry enough energy to maintain the thermal structure of the solar corona, it is not clear whether such energy can be efficiently and effectively converted into heating. Phase-mixing of Alfvén waves is considered a candidate mechanism, as it can develop transverse gradient where magnetic energy can be converted into thermal energy. However, phase-mixing is a process that crucially depends on the amplitude and period of the transverse oscillations, and only recently have we obtained a complete measurement of the power spectrum for transverse oscillations in the corona. Aims. We aim to investigate the heating generated by phase-mixing of transverse oscillations triggered by buffeting of a coronal loop that follows from the observed coronal power spectrum as well as the impact of these persistent oscillations on the structure of coronal loops. Methods. We considered a 3D MHD model of an active region coronal loop and we perturbed its footpoints with a 2D horizontal driver that represents a random buffeting motion of the loop footpoints. Our driver was composed of 1000 pulses superimposed to generate the observed power spectrum. Results. We find that the heating supply from the observed power spectrum in the solar corona through phase-mixing is not sufficient to maintain the million-degree active region solar corona. We also find that the development of Kelvin–Helmholtz instabilities could be a common phenomenon in coronal loops that could affect their apparent life time. Conclusions. This study concludes that is unlikely that phase-mixing of Alfvén waves resulting from an observed power spectrum of transverse coronal loop oscillations can heat the active region solar corona. However, transverse waves could play an important role in the development of small scale structures.

scholarly journals A study of phase-steepened Alfvén waves in a high-speed stream at 0.29 AU

2000 ◽  
Vol 18 (8) ◽  
pp. 845-851 ◽  
Author(s):  
P. Alexander
Keyword(s):  
Solar Wind ◽  
High Speed ◽  
A Priori ◽  
Solar Wind Plasma ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Interplanetary Physics ◽  
Speed Solar Wind ◽  
High Speed Solar Wind

Abstract. This work performs a search of phase-steepened Alfvén waves under a priori ideal conditions: a high-speed solar wind stream observed in one of the closest approaches to the Sun by any spacecraft (Helios 2). Five potential candidates were initially found following procedures established in earlier work. The observed cases exhibited arc-like or elliptical polarizations, and the rotational discontinuities that formed the abrupt wave edges were found at either the leading or the trailing part. The consideration of some additional specific parameters (mainly related to the relative orientation between mean magnetic field, wave and discontinuity) has been suggested here for an ultimate and proper identification of this kind of phenomenon. After the inclusion of these calculations in our analysis, even fewer cases than the five originals remain. It is suggested that optimum conditions for the detection rather than just for the existence of these events have to be reconsidered.Key words: Interplanetary physics (discontinuities; MHD waves and turbulence; solar wind plasma)

scholarly journals Toroidal and poloidal Alfvén waves with arbitrary azimuthal wavenumbers in a finite pressure plasma in the Earth's magnetosphere

2004 ◽  
Vol 22 (1) ◽  
pp. 267-287 ◽  
Author(s):  
D. Yu. Klimushkin ◽  
P. N. Mager ◽  
K.-H. Glassmeier
Keyword(s):  
Extreme Values ◽  
Second Harmonic ◽  
Alfven Waves ◽  
Wave Number ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Left Hand ◽  
Azimuthal Wave ◽  
Polarized Waves ◽  
Radially Polarized

Abstract. In this paper, in terms of an axisymmetric model of the magnetosphere, we formulate the criteria for which the Alfvén waves in the magnetosphere can be toroidally and poloidally polarized (the disturbed magnetic field vector oscillates azimuthally and radially, respectively). The obvious condition of equality of the wave frequency ω to the toroidal (poloidal) eigenfrequency ΩTN (ΩPN) is a necessary and sufficient one for the toroidal polarization of the mode and only a necessary one for the poloidal mode. In the latter case we must also add to it a significantly stronger condition ∣ΩTN–ΩPN∣/ΩTN ≫ m–1 where m is the azimuthal wave number, and N is the longitudinal wave number. In cold plasma (the plasma to magnetic pressure ratio β = 0) the left-hand side of this inequality is too small for the routinely recorded (in the magnetosphere) second harmonic of radially polarized waves, therefore these waves must have nonrealistically large values of m. By studying several models of the magnetosphere differing by the level of disturbance, we found that the left-hand part of the poloidality criterion can be satisfied by taking into account finite plasma pressure for the observed values of m ∼ 50 – 100 (and in some cases, for even smaller values of the azimuthal wave numbers). When the poloidality condition is satisfied, the existence of two types of radially polarized Alfvén waves is possible. In magnetospheric regions, where the function ΩPN is a monotonic one, the mode is poloidally polarized in a part of its region of localization. It propagates slowly across magnetic shells and changes its polarization from poloidal to toroidal. The other type of radially polarized waves can exist in those regions where this function reaches its extreme values (ring current, plasmapause). These waves are standing waves across magnetic shells, having a poloidal polarization throughout the region of its existence. Waves of this type are likely to be exemplified by giant pulsations. If the poloidality condition is not satisfied, then the mode is toroidally polarized throughout the region of its existence. Furthermore, it has a resonance peak near the magnetic shell, the toroidal eigenfrequency of which equals the frequency of the wave. Key words. Magnetospheric physics (plasmasphere; MHD waves and instabilities) – Space plasma physics (kinetic and MHD theory)

scholarly journals Phase Mixing of Propagating Alfvén Waves

1985 ◽  
Vol 107 ◽  
pp. 365-369
Author(s):  
L. Nocera ◽  
B. Leroy ◽  
E. R. Priest
Keyword(s):  
Solar Corona ◽  
Solar Atmosphere ◽  
Outer Part ◽  
Alfven Waves ◽  
Mhd Waves ◽  
Alfvén Waves ◽  
Phase Mixing ◽  
The Waves

Among MHD waves, Alfvén waves have been proved to be the best candidates to reach the solar corona and, eventually, to be responsible for the heating of this outer part of the solar atmosphere. The problem arises, however, about the mechanism able to transform the energy stored in the waves into heat.

scholarly journals On the stability of solitary kinetic Alfvén waves

1979 ◽  
Vol 73 (5-6) ◽  
pp. 389-390 ◽  
Author(s):  
J.P. Sheerin ◽  
R.S.B. Ong
Keyword(s):  
Alfven Waves ◽  
Alfvén Waves ◽  
The Stability ◽  
Kinetic Alfvén Waves
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