scholarly journals Effect of the radiative damping on magnetohydrodynamic waves in an isothermal medium

2002 ◽  
Vol 29 (6) ◽  
pp. 341-348 ◽  
Author(s):  
Hadi Alkahby ◽  
Andrew Talmadge ◽  
Abraham Jalbout
Keyword(s):  
Attenuation Factor ◽  
Heat Radiation ◽  
Heating Process ◽  
Magnetohydrodynamic Waves ◽  
Lower Region ◽  
Radiation Coefficient ◽  
Propagating Waves ◽  
Isothermal Medium ◽  
The Waves ◽  
Isothermal Atmosphere

We investigate the effect of the heat radiation on the reflection and dissipation of upward propagating waves in an isothermal atmosphere. It is shown that the magnetic field produces a totally reflecting layer. Consequently, the atmosphere can be divided into two distinct regions. In the lower region, the solution can be written as a linear combination of an upward and a downward propagating wave, and in the upper region the solution, which satisfies the upper boundary condition, decays exponentially or behaves like a constant. These two regions are connected by a region in which the reflection and transmission of the waves takes place. Moreover, the heat radiation affects only the lower region and changes the sound speed from the adiabatic value to the isothermal one. The reflection coefficient and the attenuation factor of the amplitude of the waves are derived for all values of the heat radiation coefficient. Finally, the conclusions are presented in connection with the heating process of the solar atmosphere.

scholarly journals On viscous and resistive dissipation of Alfvén waves in an isothermal atmosphere

1997 ◽  
Vol 20 (3) ◽  
pp. 605-610
Author(s):  
Hadi Yahya Alkahby
Keyword(s):  
Transition Layer ◽  
Kinematic Viscosity ◽  
Magnetic Energy ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Lower Region ◽  
Propagating Waves ◽  
The Waves ◽  
Isothermal Atmosphere ◽  
Viscosity Changes

In this article we will investigate reflection and dissipation of Alfvén waves, resulting from a uniform vertical magnetic field, in a viscous, resistive and isothermal atmosphere. It is shown that the atmosphere may be divided into two distinct regions connected by an absorbing and reflecting transition layer. In the transition layer the reflection, dissipation and absorption of the magnetic energy of the waves take place and in it the kinematic viscosity changes from small to large values. In the lower region the effect of the resistive diffusivity and kinematic viscosity changes from small to large values. In the lower region the effect of the resistive diffusivity and kinematic viscosity is negligible and in it the solution can be represented as a linear combination of two, incident and reflected, propagating waves with different wavelengths and different dissipative factors. In the upper region the effect of the resistive diffusivity and kinematic viscosity is large and the solution, which satisfies the prescribed boundary conditions, will behave as a constant. The reflection coefficient, the dissipative factors are determined and the conclusions are discussed in connection with solar heating.

scholarly journals On resistive dissipation of Alfvén waves in an isothermal atmosphere

1996 ◽  
Vol 19 (3) ◽  
pp. 587-594
Author(s):  
H. Y. Alkahby
Keyword(s):  
Transition Region ◽  
Magnetic Energy ◽  
Alfven Waves ◽  
Scale Height ◽  
Wave Number ◽  
Alfvén Waves ◽  
Propagating Waves ◽  
The Waves ◽  
Isothermal Atmosphere ◽  
Density Scale

In this paper we will examine the reflection and dissipation of Alfvén waves, resulting from a uniform vertical magnetic field, in an inviscid, resistive and isothermal atmosphere. An equation for the damping length distance that wave can travel at Alfvén speed is derived. This equation shows that the damping length is proportional to the wave number and the density scale height and it is valid not only for Alfvén waves but also for any wave that travels at Alfvén speed. Moreover, it is shown that the atmosphere may be divided into two distinct regions connected by an absorbing and reflecting transition region. In the lower region the solution can be represented as a linear combination of two, incident and reflected, propagating waves with the same wavelengths and the same dissipative factors. In the upper region the effect of the resistive diffusivity and Alfvén speed is large and the solution, which satisfies the prescribed boundary conditions, either decays with altitude or behaves as a constant. In the transition region the reflection, dissipation and absorption of the magnetic energy of the waves take place. The reflection coefficient, the dissipative factors, which are proportional to the damping length, are determined and the conclusions are discussed in connection with heating of the solar atmosphere.

Internal waves in a viscous atmosphere

1975 ◽  
Vol 72 (4) ◽  
pp. 773-786 ◽  
Author(s):  
W. L. Chang ◽  
T. N. Stevenson
Keyword(s):  
Energy Source ◽  
Incompressible Fluid ◽  
Internal Waves ◽  
Infinite Number ◽  
Similarity Solution ◽  
Small Amplitude ◽  
Horizontal Plane ◽  
Two Dimensional ◽  
The Waves ◽  
Isothermal Atmosphere

The way in which internal waves change in amplitude as they propagate through an incompressible fluid or an isothermal atmosphere is considered. A similarity solution for the small amplitude isolated viscous internal wave which is generated by a localized two-dimensional disturbance or energy source was given by Thomas & Stevenson (1972). It will be shown how summations or superpositions of this solution may be used to examine the behaviour of groups of internal waves. In particular the paper considers the waves produced by an infinite number of sources distributed in a horizontal plane such that they produce a sinusoidal velocity distribution. The results of this analysis lead to a new small perturbation solution of the linearized equations.

scholarly journals Propagation of Rossby waves in stratified shear flows

1989 ◽  
Vol 12 (3) ◽  
pp. 547-557
Author(s):  
Palani G. Kandaswamy ◽  
B. Tamil Selvi ◽  
Lokenath Debnath
Keyword(s):  
Wave Equation ◽  
Relative Frequency ◽  
Shear Flows ◽  
Rossby Waves ◽  
Zonal Flow ◽  
Single Wave ◽  
Beta Plane ◽  
Valve Effect ◽  
The Waves ◽  
Isothermal Atmosphere

A study is made of the propagation of Rossby waves in a stably stratified shear flows. The wave equation for the Rossby waves is derived in an isothermal atmosphere on a beta plane in the presence of a latitudinally sheared zonal flow. It is shown that the wave equation is singular at five critical levels, but the wave absorption takes place only at the two levels where the local relative frequency equals in magnitude to the Brunt Vaisala frequency. This analysis also reveals that these two levels exhibit valve effect by allowing the waves to penetrate them from one side only. The absorption coefficient exp(2πμ)is determined at these levels. Both the group velocity approach and single wave treatment are employed for the investigation of the problem.

scholarly journals Acoustic-gravity waves in a viscous and thermally conducting isothermal atmosphere

1995 ◽  
Vol 18 (2) ◽  
pp. 371-382 ◽  
Author(s):  
H. Y. Alkahby
Keyword(s):  
Gravity Waves ◽  
Attenuation Factor ◽  
Volume Effect ◽  
Temperature Perturbation ◽  
Oscillatory Process ◽  
Acoustic Gravity Waves ◽  
Perturbation Problem ◽  
The One ◽  
Thermally Conducting ◽  
Isothermal Atmosphere

In this paper we will investigate the effect of Newtonian cooling on the propagation of acoustic-gravity waves in a viscous and thermally conducting isothermal atmosphere for large Prandtl number and for an arbitrary values of Newtonian cooling coefficient. This problem leads to a singular perturbation problem which is solved by matching inner and outer approximations. It is shown that the viscosity creates an absorbing and reflecting layer. Below it the oscillatory process is adiabatic, for small Newtonian cooling coefficient, and above it the solution will decay to constant before it is influenced by the effect of the thermal conductivity. Newtonian cooling is a volume effect and influences mainly the lower adiabatic region, in which it causes attenuation in the amplitude of the wave. Finally it is shown that when Newtonian cooling coefficient goes to infinity it acts directly to eliminate the temperature perturbation associated with the wave and the attenuation factor in the amplitude of the wave. Accordingly the wavelength changes to the one consistent with the Newtonian sound speed. The reflection coefficient and the attenuation factor of the amplitude of the wave are derived for all values of Newtonian cooling coefficient.

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 Gravity wave generation by large scale bubbles

1988 ◽  
Vol 123 ◽  
pp. 383-386
Author(s):  
Axel Brandenburg
Keyword(s):  
Gravity Wave ◽  
Fourier Transformation ◽  
Large Scale ◽  
Lamb Waves ◽  
Vertical Direction ◽  
Hydrodynamic Equations ◽  
Propagating Waves ◽  
Pressure Scale ◽  
Isothermal Atmosphere ◽  
Small Disturbances

The response of an isothermal atmosphere to small disturbances in entropy is studied taking compressible effects fully into account. The method of Green's functions is applied to solve the linearized hydrodynamic equations by Fourier transformation. A bubble may be created by perturbing the entropy within a finite volume. At first Lamb waves will be then emitted radially and the bubble undergoes a series of Brunt-Väisälä oscillations. We find that horizontally propagating waves are generated only by large bubbles “exceeding a radius of about ten pressure scale heights, whereas smaller bubbles lead to motions propagating principally in the vertical direction.

scholarly journals Energy occupation of waves and structures in 3D compressive MHD turbulence

2019 ◽  
Vol 488 (1) ◽  
pp. 859-867 ◽  
Author(s):  
L P Yang ◽  
H Li ◽  
S T Li ◽  
L Zhang ◽  
J S He ◽  
...  
Keyword(s):  
Large Scale ◽  
Mean Field ◽  
Turbulent Energy ◽  
Mhd Turbulence ◽  
Linear Cascade ◽  
Temporal Domain ◽  
Propagating Waves ◽  
Cascade Processes ◽  
Parallel Direction ◽  
The Waves

Abstract Structures and propagating waves are often observed in solar wind turbulence. Their origins and features remain to be uncovered. In this work, we use 3D driven, compressible MHD turbulence simulations to investigate the global signatures of the driven fluctuations in whole spatial and temporal domain. With four-dimensional spatial-temporal (x, y, z, t) Fourier transformations implemented, we have identified two distinct main populations: waves, which satisfy the $\omega -\boldsymbol {k}$ dispersion relations and are propagating; and structures, which satisfy the polarization relations but non-propagating (ω = 0). Whereas the overall turbulent energy spectrum is still consistent with k−5/3, the contributions from waves and structures show very different behaviour in $\boldsymbol {k}$ space, with structures dominating at small k but waves becomes comparable to structures at large k. Overall, the fluctuations in the directions perpendicular to the large-scale mean field $\boldsymbol {B_0}$ are a manifestation of structures, while along the parallel direction, the fluctuations are dominated by waves. Also, a significant portion of the incompressible structures are the Alfvénic nature, and with imbalanced increased, the waves predominantly propagate in one direction and nearly perpendicular to $\boldsymbol {B_0}$. Differentiating the relative contributions from waves and structures could have important implications for understanding the non-linear cascade processes in the inertial range as well as particle-fluctuation interactions at small scales.

Nonlinear Landau Damping of Alfvén Waves in a High β Plasma

1982 ◽  
Vol 37 (8) ◽  
pp. 809-815 ◽  
Author(s):  
Heinrich J. Völk ◽  
Catherine J. Cesarsky
Keyword(s):  
Wave Length ◽  
Wave Spectrum ◽  
Nonlinear Damping ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Propagating Waves ◽  
Damping Rate ◽  
Nonlinear Landau Damping ◽  
The Waves ◽  
The Magnetic Field

A study is made of the nonlinear damping of parallel propagating Alfvén waves in a high β plasma. Two circularly polarized parallel propagating waves give rise to a beat wave, which in general contains both a longitudinal electric field component and a longitudinal gradient in the magnetic field strength. The wave damping is due to the interactions of thermal particles with these fields. If the amplitudes of the waves are low, a given wave (ω1, k1) is damped by the presence of all longer wavelength waves; thus, if the amplitudes of the waves in the wave spectrum increase with wave length, the effect of the longest waves is dominant.However, when the amplitude of the waves is sufficiently high, the particles are trapped in the wave packets, and the damping rate may be considerably reduced. We calculate the induced electrostatic field, and examine the trapping of thermal particles in a pair of waves. Finally, we give examples of modified damping rates of a wave in the presence of a spectrum of waves, and show that, when the trapping is effective, the waves are mostly damped by their interactions with waves of comparable wavelengths

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