scholarly journals The temporal behaviour of MHD waves in a partially ionized prominence-like plasma: Effect of heating and cooling

2017 ◽  
Vol 609 ◽  
pp. A6 ◽  
Author(s):  
J. L. Ballester ◽  
M. Carbonell ◽  
R. Soler ◽  
J. Terradas
Keyword(s):  
Temporal Variation ◽  
Mhd Equations ◽  
Time Dependent ◽  
Mhd Waves ◽  
Physical Situation ◽  
Fast Wave ◽  
Ionization Degree ◽  
Specific Internal Energy ◽  
Temporal Behaviour ◽  
Partially Ionized

Context. During heating or cooling processes in prominences, the plasma microscopic parameters are modified due to the change of temperature and ionization degree. Furthermore, if waves are excited on this non-stationary plasma, the changing physical conditions of the plasma also affect wave dynamics. Aims. Our aim is to study how temporal variation of temperature and microscopic plasma parameters modify the behaviour of magnetohydrodynamic (MHD) waves excited in a prominence-like hydrogen plasma. Methods. Assuming optically thin radiation, a constant external heating, the full expression of specific internal energy, and a suitable energy equation, we have derived the profiles for the temporal variation of the background temperature. We have computed the variation of the ionization degree using a Saha equation, and have linearized the single-fluid MHD equations to study the temporal behaviour of MHD waves. Results. For all the MHD waves considered, the period and damping time become time dependent. In the case of Alfvén waves, the cut-off wavenumbers also become time dependent and the attenuation rate is completely different in a cooling or heating process. In the case of slow waves, while it is difficult to distinguish the slow wave properties in a cooling partially ionized plasma from those in an almost fully ionized plasma, the period and damping time of these waves in both plasmas are completely different when the plasma is heated. The temporal behaviour of the Alfvén and fast wave is very similar in the cooling case, but in the heating case, an important difference appears that is related with the time damping. Conclusions. Our results point out important differences in the behaviour of MHD waves when the plasma is heated or cooled, and show that a correct interpretation of the observed prominence oscillations is very important in order to put accurate constraints on the physical situation of the prominence plasma under study, that is, to perform prominence seismology.

scholarly journals Dynamical Effects in Solar Photospheric Flux Tubes

1996 ◽  
Vol 154 ◽  
pp. 155-158
Author(s):  
S.S. Hasan
Keyword(s):  
Flux Tube ◽  
Ambient Medium ◽  
Resonant Interaction ◽  
Scale Height ◽  
Mhd Equations ◽  
Time Dependent ◽  
Radiative Transport ◽  
Local Pressure ◽  
Flux Tubes ◽  
Pressure Scale

AbstractThe interaction of an intense flux tube, extending vertically through the photosphere, with p-modes in the ambient medium is modelled by solving the time dependent MHD equations in the thin flux tube approximation. It is found that a resonant interaction can occur, which leads to the excitation of flux tube oscillations with large amplitudes. The resonance is not as sharp as in the case of an unstratified atmosphere, but is broadened by a factor proportional to H−2, where H is the local pressure scale height. In addition, the inclusion of radiative transport leads to a decrease in the amplitude of the oscillations, but does not qualitatively change the nature of the interaction.

A MATHEMATICAL MODEL FOR ANALYSIS OF WAVE PROPAGATION IN A LINEARIZED VERTICALLY NONUNIFORM PARTIALLY IONIZED GAS

1966 ◽  
Vol 44 (5) ◽  
pp. 1047-1065 ◽  
Author(s):  
Harold R. Raemer
Keyword(s):  
Wave Propagation ◽  
Differential Equations ◽  
Numerical Solutions ◽  
Mhd Waves ◽  
Mathematical Treatment ◽  
Algebraic Differential Equation ◽  
Neutral Gas ◽  
Partially Ionized ◽  
Analytical Approaches ◽  
Adiabatic State

Wave propagation in fully and partially ionized gases, with and without magnetic fields, has been treated by several workers; e.g., Tanenbaum and Mintzer (1962) obtained dispersion relations for a linearized and spatially uniform gas of electrons, positive ions, and neutrals. The present paper discusses the basic formulation and mathematical treatment of wave propagation in a linearized electron – ion – neutral gas, with static magnetic field, in which ambient-gas parameters vary arbitrarily vertically and are uniform horizontally.A standard formulation of the general problem is discussed via Boltzmann and Maxwell equations. By momentum-space averaging, the Boltzmann equation yields motion, continuity, and dynamic adiabatic state equations. These are combined to yield neutral and plasma equations of motion, continuity, and adiabatic state and a generalized Ohm's Law. Steady-state plane-wave solutions of the form exp[−i(ωt – kxx)] are assumed, reducing the x, y, and t dependence to algebraic relations, but the equations remain differential in z. The system consists of 10 simultaneous coupled ordinary first-order complex differential equations and 11 simultaneous complex algebraic equations in 21 complex unknowns.The second part of the paper is a discussion of the solution of this coupled algebraic differential equation system, equivalent to the system arising in the analysis of coupled linear electrical networks. Referring to the literature of differential equations and modern automatic control systems, various purely analytical approaches are discussed with emphasis on their deficiencies in obtaining practical numerical results with an arbitrary z variation. The Runge–Kutta step-by-step-procedure was invoked eventually and a Fortran program based on this technique was written. The program can be used to obtain accurate numerical solutions to many problems involving wave propagation in a linearized, vertically nonuniform electron – ion – neutral gas without requiring drastic simplifying assumptions for the vertical nonuniformity. This program can be used, by changing input parameter values, to treat such diverse problems as the perturbing effect of acoustic–gravity waves on ionospheric electron density, electromagnetic wave propagation in the vertically inhomogeneous ionosphere, MHD waves high in the ionosphere, or various kinds of wave propagation in prepared plasmas with a one-dimensional inhomogeneity. Numerical solutions for the acoustic – gravity wave – plasma interaction problem and their interpretation will be reported in a later paper.

scholarly journals Nonlinear theory of non-axisymmetric resonant slow waves in straight magnetic flux tubes

2000 ◽  
Vol 64 (5) ◽  
pp. 579-599 ◽  
Author(s):  
I. BALLAI ◽  
R. ERDÉLYI ◽  
M. GOOSSENS
Keyword(s):  
Solar Phys ◽  
Normal Component ◽  
Mhd Equations ◽  
Mhd Waves ◽  
Mean Flow ◽  
Slab Geometry ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
Field Lines ◽  
Connection Formulae

Nonlinear resonant slow magnetohydrodynamic (MHD) waves are studied in weakly dissipative isotropic plasmas for a cylindrical equilibrium model. The equilibrium magnetic field lines are unidirectional and parallel with the z axis. The nonlinear governing equations for resonant slow magnetoacoustic (SMA) waves are derived. Using the method of matched asymptotic expansions inside and outside the narrow dissipative layer, we generalize the connection formulae for the Eulerian perturbation of the total pressure and for the normal component of the velocity. These nonlinear connection formulae in dissipative cylindrical MHD are an important extention of the connection formulae obtained in linear ideal MHD [Sakurai et al., Solar Phys. 133, 227 (1991)], linear dissipative MHD [Goossens et al., Solar Phys. 175, 75 (1995); Erdélyi, Solar Phys. 171, 49 (1997)] and in nonlinear dissipative MHD derived in slab geometry [Ruderman et al., Phys. Plasmas4, 75 (1997)]. These generalized connection formulae enable us to connect the solutions at both sides of the dissipative layer without solving the MHD equations in the dissipative layer. We also show that the nonlinear interaction of harmonics in the dissipative layer is responsible for generating a parallel mean flow outside the dissipative layer.

scholarly journals THE TIME-DEPENDENT ONE-ZONE HADRONIC MODEL: FIRST PRINCIPLES

2012 ◽  
Vol 08 ◽  
pp. 19-24 ◽  
Author(s):  
STAVROS DIMITRAKOUDIS ◽  
MARIA PETROPOULOU ◽  
APOSTOLOS MASTICHIADIS
Keyword(s):  
Magnetic Field ◽  
First Principles ◽  
Kinetic Equations ◽  
Time Dependent ◽  
Accurate Description ◽  
Temporal Behaviour ◽  
Spherical Volume ◽  
The One ◽  
Hadronic Model

We present some results on the radiative signatures of the one zone hadronic model. For this we have solved five spatially averaged, time-dependent coupled kinetic equations which describe the evolution of relativistic protons, electrons, photons, neutrons and neutrinos in a spherical volume containing a magnetic field. Protons are injected and lose energy by synchrotron, photopair and photopion production. We model photopair and photopion using the results of relevant MC codes, like the SOPHIA code in the case of photopion, which give accurate description for the injection of secondaries which then become source functions in their respective equations. This approach allows us to calculate the expected photon and neutrino spectra simultaneously in addition to examining questions like the efficiency and the temporal behaviour of the hadronic models.

Time-dependent solutions of the Navier–Stokes equations for spatially-uniform velocity gradients

1994 ◽  
Vol 124 (1) ◽  
pp. 127-136 ◽  
Author(s):  
A. D. D. Craik
Keyword(s):  
Fluid Flow ◽  
Incompressible Fluid ◽  
Stokes Equations ◽  
Time Dependent ◽  
Navier Stokes ◽  
Incompressible Fluid Flow ◽  
Navier Stokes Equations ◽  
Temporal Behaviour ◽  
Uniform Velocity ◽  
Velocity Gradients

Classes of exact solutions of the Navier–Stokes equations for incompressible fluid flow are explored. These have spatially-uniform velocity gradients at each instant, but often display complex temporal behaviour. Particular illustrative cases are described and related to previously-known solutions.

scholarly journals Gravitational instability on propagation of MHD waves in astrophysical plasma

2013 ◽  
Vol 79 (5) ◽  
pp. 805-816 ◽  
Author(s):  
ALEMAYEHU MENGESHA CHERKOS ◽  
S. B. TESSEMA
Keyword(s):  
Magnetic Field ◽  
Dispersion Relation ◽  
Gravitational Instability ◽  
Mhd Equations ◽  
Mhd Waves ◽  
Anisotropic Pressure ◽  
Heat Conducting ◽  
Magnetic Field Direction ◽  
Pressure Tensor ◽  
Astrophysical Plasma

AbstractWe determine the general dispersion relation for the propagation of magnetohydrodynamic (MHD) waves in astrophysical plasma by considering the effect of gravitational instability and viscosity with anisotropic pressure tensor and heat-conducting plasma. Basic MHD equations have been derived and linearized by the method of perturbation to develop the general form of dispersion relation equation. Our result indicates that the transverse propagation of waves in such a plasma is affected by the inclusion of heat conduction. For wave propagation, parallel to the magnetic field direction, we find that the fairhose mode is unaffected, whereas the mode corresponding to the gravitational instability is modified in astrophysical plasma with anisotropic pressure tensor being stable in the presence of viscosity and strong magnetic field at considerable wavelength.

scholarly journals Collisional and viscous damping of MHD waves in partially ionized plasmas of the solar atmosphere

2004 ◽  
Vol 422 (3) ◽  
pp. 1073-1084 ◽  
Author(s):  
M. L. Khodachenko ◽  
T. D. Arber ◽  
H. O. Rucker ◽  
A. Hanslmeier
Keyword(s):  
Solar Atmosphere ◽  
Mhd Waves ◽  
Viscous Damping ◽  
Ionized Plasmas ◽  
Partially Ionized Plasmas ◽  
Partially Ionized

scholarly journals Partially ionized layers of accreted envelopes of weakly and strongly magnetized neutron stars

2000 ◽  
Vol 177 ◽  
pp. 619-620 ◽  
Author(s):  
Alexander Potekhin ◽  
Gilles Chabrier ◽  
Yuri Shibanov
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Strong Field ◽  
Ionization Degree ◽  
Occupation Numbers ◽  
Partially Ionized

AbstractWe study equilibrium properties of partially ionized hydrogen atmospheres and subphotospheric layers of weakly (with magnetic fieldB≪ 109G) and strongly (B≫ 1010G) magnetized neutron stars. In both weak- and strong-field cases, the ionization degree, atomic occupation numbers, and equation of state are calculated. These results are used to calculate opacities of neutron-star atmospheres.

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