Generation and propagation of Alfvén waves in solar atmosphere

AbstractThe propagation of Alfvén waves from the photosphere into the corona with regard to the fine structure of the magnetic field is considered. The energy flux of Alfvén–type waves generated in the photosphere by convective motions does not depend on the ionization ratio. The reflection coefficient continuously decreases with a decrease of wave period. Influence of the external magnetic field on the Spruit cutoff frequency for transverse (kink) modes excited in the thin magnetic flux tubes is analyzed. Torsional modes can penetrate into the upper atmosphere most effectively since their amplitudes does not increase with height in the photosphere while kink ones can be transformed into shock waves in the lower chromosphere because of a significant increase of amplitudes. In spite of stratification the linearity of Alfvén–type modes in the chromosphere is conserved due to violation of the WKB approximation. The important role of the magnetic canopy is discussed. Alfvén waves generated by convective motions in the photosphere can contribute significantly to the heating of the coronal plasma in quite regions of the Sun.

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V. Heating and Dynamics of Chromosphere and Corona

Transactions of the International Astronomical Union ◽

10.1017/s0251107x00007021 ◽

1988 ◽

Vol 20 (1) ◽

pp. 100-102

Author(s):

G.E. Brueckner

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Acoustic Waves ◽

Convection Zone ◽

Flux Tubes ◽

Magnetic Structures ◽

Convective Motions ◽

Field Lines ◽

The Magnetic Field

The crucial role of magnetic fields in any mechanism to heat the outer solar atmosphere has been generally accepted by all authors. However, there is still no agreement about the detailed function of the magnetic field. Heating mechanisms can be divided up into 4 classes: (I) The magnetic field plays a passive role as a suitable medium for the propagation of Alfvén waves from the convection zone into the corona (Ionson, 1984). (II) In closed magnetic structures the slow random shuffling of field lines by convective motions below the surface induces electric currents in the corona which heat it by Joule dissipation (Heyvaerts and Priest, 1984). (Ill) Emerging flux which is generated in the convection zone reacts with ionized material while magnetic field lines move through the chromosphere, transition zone and corona. Rapid field line annihilation, reconnection and drift currents result in heating and material ejection (Brueckner, 1987; Brueckner et al., 1987; Cook et al., 1987). (IV) Acoustic waves which could heat the corona can be guided by magnetic fields. Temperature distribution, wave motions and shock formation are highly dependent on the geometry of the flux tubes (Ulmschneider and Muchmore, 1986; Ulmschneider, Muchmore and Kalkofen, 1987).

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TRANSVERSE WAVES PROPAGATING ALONG AN APPLIED MAGNETIC FIELD IN A PLASMA

Canadian Journal of Physics ◽

10.1139/p64-084 ◽

1964 ◽

Vol 42 (5) ◽

pp. 906-917

Author(s):

R. E. Burgess ◽

J. G. Cook

Keyword(s):

Magnetic Field ◽

Dispersion Equation ◽

Applied Magnetic Field ◽

Equation Of Motion ◽

Alfven Waves ◽

Alfven Wave ◽

Alfvén Waves ◽

Transverse Waves ◽

The Magnetic Field

Transverse waves propagating along an applied magnetic field are studied, with special attention to the role of the magnetic field in determining the behavior of the wave. No restrictions are placed on the hole (or ion) mass, and the electron and hole densities may differ. The behavior of the magnetic-field-dominated waves is studied, and it is shown that it is profitable to extend the concept of an Alfvén wave to include those waves for which essentially B0 instead of B02 appears in the dispersion equation. Both intrinsic and extrinsic cases are studied.The dispersion equation approach is compared with the equation of motion and Ohm's law approach used by Watanabe for a study of Alfvén waves, and Watanabe's starting equations are generalized to make a study of Alfvén waves in solid-state plasmas with Watanabe's approach possible.

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Concerning the Dynamics of Energetic Protons in Coronal Magnetic Loops: Dispersion Effects of Alfven Waves

Symposium - International Astronomical Union ◽

10.1017/s007418090007618x ◽

1985 ◽

Vol 107 ◽

pp. 559-559

Author(s):

V. A. Mazur ◽

A. V. Stepanov

Keyword(s):

Magnetic Field ◽

Wave Dispersion ◽

Alfven Waves ◽

Alfven Wave ◽

Wave Number ◽

Alfvén Waves ◽

Coronal Loops ◽

Coronal Magnetic Loops ◽

The Magnetic Field ◽

Solar Coronal

It is shown that the existence of plasma density inhomogeneities (ducts) elongated along the magnetic field in coronal loops, and of Alfven wave dispersion, associated with the taking into account of gyrotropy U ≡ ω/ωi ≪ 1 (Leonovich et al., 1983), leads to the possibility of a quasi-longitudinal k⊥ < √U k‖ propagation (wave guiding) of Alfven waves. Here ω is the frequency of Alfven waves, ωi is the proton gyrofrequency, and k is the wave number. It is found that with the parameter ξ = ω2 R/ωi A > 1, where R is the inhomogeneity scale of a loop across the magnetic field, and A is the Alfven wave velocity, refraction of Alfven waves does not lead, as contrasted to Wentzel's inference (1976), to the waves going out of the regime of quasi-longitudinal propagation. As the result, the amplification of Alfven waves in solar coronal loops can be important. A study is made of the cyclotron instability of Alfven waves under solar coronal conditions.

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Alfvén Waves in Dusty Interstellar Clouds

Publications of the Astronomical Society of Australia ◽

10.1071/as97170 ◽

1997 ◽

Vol 14 (2) ◽

pp. 170-178 ◽

Cited By ~ 15

Author(s):

N. F. Cramer ◽

S. V. Vladimirov

Keyword(s):

Magnetic Field ◽

Negative Charge ◽

Alfven Waves ◽

Dust Particles ◽

Alfvén Waves ◽

Interstellar Clouds ◽

General Dispersion ◽

The Right ◽

The Magnetic Field ◽

Field Wave

AbstractDust particles in a plasma can be higWy charged, and can carry a proportion of the negative charge of the plasma. Even if this proportion is quite small, as in interstellar dusty clouds, it can have a large effect on hydromagnetic Alfvén waves propagating at frequencies well below the ion–cyclotron frequency. In particular, the right-hand circularly polarised mode experiences a cutoff due to the presence of the dust. We generalise previous work on Alfvén waves in dusty interstellar plasmas by considering the general dispersion relation for waves propagating at an arbitrary angle with respect to the magnetic field. Wave energy propagating at oblique angles to the magnetic field in an increasing density gradient can be very efficiently damped by the Alfvén resonance absorption process in a dusty plasma, and we consider this damping mechanism for waves in interstellar clouds.

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Effect of the magnetic field curvature on the generation of zonal flows by drift-Alfvén waves

Plasma Physics Reports ◽

10.1134/s1063780x07050066 ◽

2007 ◽

Vol 33 (5) ◽

pp. 407-419 ◽

Cited By ~ 4

Author(s):

A. B. Mikhailovskii ◽

E. A. Kovalishen ◽

M. S. Shirokov ◽

V. S. Tsypin ◽

R. M. O. Galvão

Keyword(s):

Magnetic Field ◽

Alfven Waves ◽

Alfvén Waves ◽

Zonal Flows ◽

Field Curvature ◽

The Magnetic Field

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What are the Radio Filaments Near the Galactic Center?

Symposium - International Astronomical Union ◽

10.1017/s0074180900229756 ◽

1996 ◽

Vol 169 ◽

pp. 247-261 ◽

Cited By ~ 1

Author(s):

Mark Morris

Keyword(s):

Magnetic Field ◽

Galactic Center ◽

Galactic Plane ◽

Local Source ◽

Flux Tubes ◽

Flux Lines ◽

Magnetic Flux Tubes ◽

The Magnetic Field ◽

Relativistic Particles ◽

Projected Distance

A population of nonthermally-emitting radio filaments tens of parsecs in length has been observed within a projected distance of ∼130 pc of the Galactic center. More or less perpendicular to the Galactic plane, they appear to define the flux lines of a milligauss magnetic field. The characteristics of the known filaments are summarized. Three fundamental questions raised by these structures are discussed: 1) Do they represent magnetic flux tubes embedded within an ubiquitous, dipole magnetic field permeating the inner Galaxy, but which have been illuminated by some local source of relativistic particles, or are they instead isolated, self-sustaining current paths with an approximately force-free magnetic configuration in pressure equilibrium with the interstellar medium? 2) What is the source of either the magnetic field or the current? and 3) What is the source of the relativistic particles which provide the illuminating synchrotron radiation? We are nearer an answer to the the last of these questions than to the others, although several interesting models have been proposed.

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Solar and stellar magnetic flux tubes

Symposium - International Astronomical Union ◽

10.1017/s0074180900083236 ◽

1996 ◽

Vol 176 ◽

pp. 201-216

Author(s):

Sami K. Solanki

Keyword(s):

Magnetic Field ◽

Magnetic Properties ◽

Magnetic Flux ◽

Large Range ◽

The Sun ◽

Flux Tubes ◽

Magnetic Elements ◽

Turbulent Pressure ◽

Magnetic Flux Tubes ◽

The Magnetic Field

The magnetic field of the Sun is mainly concentrated into intense magnetic flux tubes having field strengths of the order of 1 kG. In this paper an overview is given of the thermal and magnetic properties of these flux tubes, which are known to exhibit a large range in size, from the smallest magnetic elements to sunspots. Differences and similarities between the largest and smallest features are stressed. Some thoughts are also presented on how the properties of magnetic flux tubes are expected to scale from the solar case to that of solar-like stars. For example, it is pointed out that on giants and supergiants turbulent pressure may dominate over gas pressure as the main confining agent of the magnetic field. Arguments are also presented in favour of a highly complex magnetic geometry on very active stars. Thus the very large starspots seen in Doppler images probably are conglomerates of smaller (but possibly still sizable) spots.

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Concerning the Dynamics of Energetic Protons in Coronal Magnetic Loops: Dispersion Effects of Alfven Waves

Symposium - International Astronomical Union ◽

10.1017/s0074180900076105 ◽

1985 ◽

Vol 107 ◽

pp. 559-559

Author(s):

V. A. Mazur ◽

A. V. Stepanov

Keyword(s):

Magnetic Field ◽

Wave Dispersion ◽

Alfven Waves ◽

Alfven Wave ◽

Wave Number ◽

Alfvén Waves ◽

Coronal Loops ◽

Coronal Magnetic Loops ◽

The Magnetic Field ◽

Solar Coronal

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A note on the modulational instability of long Alfvén waves parallel to the magnetic field

Journal of Plasma Physics ◽

10.1017/s0022377800021267 ◽

1978 ◽

Vol 19 (3) ◽

pp. 437-447 ◽

Cited By ~ 60

Author(s):

Einar Mjølhus

Keyword(s):

Magnetic Field ◽

Inverse Scattering ◽

Modulational Instability ◽

Alfven Waves ◽

Alfvén Waves ◽

Stable Case ◽

Unstable Case ◽

Modulational Stability ◽

Limiting Case ◽

The Magnetic Field

An amplitude dependent criterion for modulational stability of long Alfvén waves parallel to the magnetic field is interpreted in terms of a recently obtained inverse scattering solution to the modified nonlinear Schrödinger equation. It is found that the solitons formed are of two types. In the strongly unstable case, normal solitons are formed. In the transition region of weakly unstable and stable cases, the anomalous type, which in a limiting case becomes the algebraic soliton, dominates. In the strongly stable case, no solitons are formed.

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