scholarly journals Mode Coupling in the Solar Corona. IV. Magnetohydrodynamic Waves

1977 ◽  
Vol 30 (6) ◽  
pp. 647 ◽  
Author(s):  
DB Melrose ◽  
MA Simpson
Keyword(s):  
General Theory ◽  
Solar Corona ◽  
Mode Coupling ◽  
Stratified Medium ◽  
Mhd Waves ◽  
Fast Mode ◽  
Slow Mode ◽  
Magnetohydrodynamic Waves ◽  
Quartic Equation ◽  
Obliquely Incident

A general theory for coupling between MHD waves obliquely incident on a stratified medium is developed. Coupling between the Alfvtln mode and the magnetoacoustic mode (the fast mode for VA > cs and the slow mode for VA < cs) is affected little by the finiteness of Cs/VA for VA >> Cs and the coupling becomes weaker as Cs/VA is increased towards unity. Coupling between the fast and slow modes for VA ≈ C. is discussed qualitatively using solutions of the MHD counterpart of the Booker quartic equation.

scholarly journals Mode Coupling in the Solar Corona. V. Reduction of the Coupled Equations

1977 ◽  
Vol 30 (6) ◽  
pp. 661 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Solar Corona ◽  
Mode Coupling ◽  
Mhd Waves ◽  
Fast Mode ◽  
Coupling Theory ◽  
Mode Coupling Theory ◽  
Coupled Equations

A simplified version of the mode-coupling theory of Clemmow and Heading is developed by reducing the set of coupled equations to two for the magnetoionic theory and three for the MHD theory. The simplified theory reproduces known results for coupling in the neighbourhood of coupling points. It is used to treat coupling between the MHD waves, and it is found that coupling between the fast mode and the Alfven mode for VA ;?; C, is stronger than the coupling between any other pair of modes. The strongest coupling of all is between the Alfven and slow (magnetoacoustic) modes for VA ~ C,.

scholarly journals Galactic Center threads as nuclear magnetohydrodynamic waves

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Magnetic Field ◽  
Supernova Remnants ◽  
Galactic Center ◽  
Mhd Waves ◽  
Fast Mode ◽  
Magnetohydrodynamic Waves ◽  
Compression Waves ◽  
Sgr A ◽  
The Waves ◽  
The Magnetic Field

Abstract Propagation of fast-mode magnetohydrodynamic (MHD) compression waves is traced in the Galactic Center with a poloidal magnetic cylinder. MHD waves ejected from the nucleus are reflected and guided along the magnetic field, exhibiting vertically stretched fronts. The radio threads and non-thermal filaments are explained as due to tangential views of the waves driven by sporadic activity in Sgr A$^*$, or by multiple supernovae. In the latter case, the threads could be extremely deformed relics of old supernova remnants exploded in the nucleus.

scholarly journals Mode-Coupled MHD Waves in the Corona and Solar Wind

1980 ◽  
Vol 91 ◽  
pp. 139-141
Author(s):  
M. Heinemann ◽  
S. Olbert
Keyword(s):  
Solar Wind ◽  
Mode Coupling ◽  
Wkb Approximation ◽  
Mhd Waves ◽  
Fast Mode ◽  
Compressional Waves

The purpose of this paper is to outline a model of mode-coupled MHD compressional waves in the corona and solar wind. The eventual aim of this work is to be able to compute how MHD waves propagate through the corona and into the solar wind beginning with a source of Alfven or fast mode waves at the base of the corona. The necessity for consideration of mode coupling arises because of typical scalelengths in the corona. For wave sources, such as supergranulation, with wave periods of about a day, the different modes do no propagate independently, as in the WKB approximation, but are coupled because the ratio of wavelength to scalelength is of the order of one or greater.

scholarly journals The generation of dense cores and substructure within them by MHD waves

2006 ◽  
Vol 2 (S237) ◽  
pp. 486-486
Author(s):  
S. Van Loo ◽  
S. A. E. G. Falle ◽  
T. W. Hartquist
Keyword(s):  
High Density ◽  
Mhd Waves ◽  
Fast Mode ◽  
Slow Mode ◽  
Dense Cores

AbstractBy using 2D simulations, we examine the generation of dense cores and substructures by magnetosonic waves. We find that the excitation of slow-mode waves by fast-mode waves produces these high-density structures.

Slow magnetohydrodynamic waves in the solar atmosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 447-460 ◽  
Author(s):  
B Roberts
Keyword(s):  
Solar Atmosphere ◽  
Gordon Equation ◽  
Observational Evidence ◽  
Stratified Medium ◽  
Coronal Loops ◽  
Slow Mode ◽  
Magnetohydrodynamic Equations ◽  
Magnetohydrodynamic Waves ◽  
Klein Gordon ◽  
Special Case

There is increasingly strong observational evidence that slow magnetoacoustic modes arise in the solar atmosphere, either as propagating or standing waves. Sunspots, coronal plumes and coronal loops all appear to support slow modes. Here we examine theoretically how the slow mode may be extracted from the magnetohydrodynamic equations, considering the special case of a vertical magnetic field in a stratified medium: the slow mode is described by the Klein–Gordon equation. We consider its application to recent observations of slow waves in coronal loops.

A general theory of self-similar expansion waves in magnetohydrodynamic flows

2001 ◽  
Vol 66 (4) ◽  
pp. 239-257 ◽  
Author(s):  
M. G. G. T. TAYLOR ◽  
P. J. CARGILL
Keyword(s):  
Magnetic Field ◽  
General Theory ◽  
Critical Point ◽  
Mhd Equations ◽  
Fast Mode ◽  
Slow Mode ◽  
Mode Wave ◽  
Expansion Waves ◽  
Self Similar ◽  
The Magnetic Field

Abstract. The general theory of self-similar magnetohydrodynamic (MHD) expansion waves is presented. Building on the familiar hydrodynamic results, a complete range of possible field–flow and wave-mode orientations are explored. When the magnetic field and flow are parallel, only the fast-mode wave can undergo an expansion to vacuum conditions: the self-similar slow-mode wave has a density that increases monotonically. For fast-mode waves with the field at an arbitrary angle with respect to the flow, the MHD equations have a critical point. There is a unique solution that passes through the critical point that has ½γβ = 1 and Br = 0 there, where γ is the polytropic index, β the local plasma beta and Br the radial component of the magnetic field. The critical point is an umbilical point, where sound and Alfvén speeds are equal, and the transcritical solution undergoes a change from a fast-mode to a slow-mode expansion at the critical point. Slow-mode expansions exist for field-flow orientations where the angle between field and flow lies either between 90° and 180° or between 270° and 360°. There is also an umbilic point in these solutions when the initial plasma beta β0 exceeds a critical value βcrit. When β0 [ges ] βcrit, the solutions require a transition through a critical point. When β0 < βcrit, there is a smooth solution involving an inflection in the density and angular velocity. For other angles between field and flow, all the slow-mode waves are compressive. An analytic solution for the case of a magnetic field everywhere perpendicular to the flow with γ = 2 is presented.

scholarly journals Mode Coupling in the Solar Corona. III. Alfvén and Magnetoacoustic Waves

1977 ◽  
Vol 30 (4) ◽  
pp. 495 ◽  
Author(s):  
DB Melrose
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Acoustic Waves ◽  
Mode Coupling ◽  
Stratified Medium ◽  
Magnetoacoustic Waves ◽  
Field Lines ◽  
Hydromagnetic Waves ◽  
Special Case ◽  
The Magnetic Field

Coupling between Alfven waves and fast mode waves obliquely incident on a stratified medium is treated using the method of Clemmow and Heading (1954) within the framework of the cold plasma approximation. A result due to Frisch (1964) is rederived in the special case of vertical incidence. The coupling is strongest for nearly parallel (to the magnetic field lines) propagation, and the coupling ratio may be approximated by Q = (00 /0)" where 0 is the angle between the wave vector and the magnetic field lines, while og = A/L, with A the wavelength and L the scalelength of the inhomogeneity. This result may be of significance in connection with the heating of the solar corona by the dissipation of waves generated initially as acoustic waves in the photosphere, and perhaps with the propagation of hydromagnetic waves in the interplanetary medium.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

1994 ◽  
Vol 144 ◽  
pp. 503-505
Author(s):  
R. Erdélyi ◽  
M. Goossens ◽  
S. Poedts
Keyword(s):  
Resonant Absorption ◽  
Numerical Code ◽  
Mhd Waves ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Element Discretization ◽  
Flux Tubes ◽  
Magnetohydrodynamic Waves ◽  
Viscosity Coefficients ◽  
Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

scholarly journals Prominence Seismology

2013 ◽  
Vol 8 (S300) ◽  
pp. 30-39 ◽  
Author(s):  
J. L. Ballester
Keyword(s):  
Solar Corona ◽  
Small Amplitude ◽  
Dense Plasma ◽  
Mhd Waves ◽  
Physical Parameters ◽  
Solar Prominences ◽  
Dynamic Structures

AbstractQuiescent solar prominences are cool and dense plasma clouds located inside the hot and less dense solar corona. They are highly dynamic structures displaying flows, instabilities, oscillatory motions, etc. The oscillations have been mostly interpreted in terms of magnetohydrodynamic (MHD) waves, which has allowed to perform prominence seismology as a tool to determine prominence physical parameters difficult to measure. Here, several prominence seismology applications to large and small amplitude oscillations are reviewed.

Propagation of magnetodynamic waves into a collisionless current layer

1976 ◽  
Vol 15 (3) ◽  
pp. 389-394 ◽  
Author(s):  
A. Hruška
Keyword(s):  
Magnetic Field ◽  
Current Layer ◽  
Fast Mode ◽  
Slow Mode ◽  
Field Aligned Current ◽  
The Waves

In a layer of magnetic field aligned current, waves corresonding to the slow mode in the limit of no current are absorbed and/or reflected as soon as they enter the layer, while, under certain conditions, the waves corresponding to the fast mode do propagate through the layer.

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