Self-similar magnetogasdynamic cylindrical shock waves,I

Similarity solutions describing the flow of a perfect gas behind a cylindrical shock wave with transverse magnetic field are investigated in an inhomogeneous medium. The total energy of the shock wave is assumed to be constant. A comparative study has been made between the results with and without magnetic field.     

Propagation of cylindrical shock waves in magnetogasdynamics

Using a well-known similarity method, different aspects of cylindrical shock waves in magnetogasdynamics are investigated. Weak and strong shocks have been discussed in strong magnetic field. Combined effects of both the components of magnetic field on flow variables are studied.     

The structure of strong hydromagnetic shock waves in a thermally-radiating gas

The structure of strong shock waves in a thermally-radiating and electrically-conducting fluid is studied by method of asymptotic matching principle. It is assumed that upstream of the shock the gas is cold and does not radiate thermally while the Mach number (M) is very high so that after being shocked the gas now thermally radiates. The viscosity of the gas () depends on temperature (T) in the simple manner T where is a constant exponent. The problem is worthy of note in high-temperature phenomena in hypersonic flow.     

Numerical investigations of converging cylindrical and spherical shock waves

The converging cylindrical and spherical shock waves have been numerically simulated. The flow is created by rupturing the diaphragm. The behaviour of the solution in the focussing stage is closely investigated and compared with the other results. An invariant difference scheme of Rusanov is used to follow the propagation of the shock wave. The study includes not only the moderate initial pressure ratio but also pressure ratios amounting up to thousands. The same scheme has been used from the initial stage of the focussing stage near the axis.     

Self-similar flows behind cylindrical shock waves in magnetogasdynamics

A comparative study has been made between the effects of transverse and axial components of the magnetic field on the self-similar flow variables of the field behind the cylindrical shock waves propagating into a non-uniform atmosphere at rest. The total energy of the wave is constant.     

Propagation of magnetoacoustic shock waves in cylindrical geometry

Cylindrical Korteweg-de Vries-Burgers (cKdVB) equation for magnetoacoustic wave is derived for dissipative magneto plasmas. Two fluid collisionless electromagnetic model is considered and reductive perturbation method is employed to study the propagation of magnetoacoustic shock waves in cylindrical geometry. Two level finite difference method is employed by using Runge-Kutta method to solve cKdVB equation numerically. The effects of nonplanar geometry, plasma density, magnetic field strength, temperature dependence and kinematic viscosity on magnetoacoustic shocks are investigated. The numerical results are also presented for illustration.     

Self-similar cylindrical shock waves with radiation heat flux

Similarity solutions describing the flow of a perfect gas behind cylindrical shock waves with radiation heat flux are investigated. The total energy of the expanding wave has been supposed to remain constant. The solution, however, is only applicable to a gaseous medium where the undisturbed pressure falls as the inverse square of the distance from the line of explosion.     

On the energy dissipation of fast hydromagnetic shock waves in the solar chromosphere

MHD equations including dissipation terms are applied to study the most important irreversible processes occurring in fast hydromagnetic shock waves under the conditions of the outer solar atmosphere. The atmosphere is assumed to be permeated by a nearly horizontal, uniform magnetic field, the magnitude and inclination angle of which being parameters of the analysis. Numerical examples, corresponding to situations which might occur in the upper chromosphere, are computed in order to demonstrate the procedure.     

Converging magnetogasdynamic cylindrical shock waves in a uniform atmosphere

A self-similar solution to the problem of the implosion of a cylindrical shock wave in the presence of a magnetic field has been investigated. A strong shock wave in a cylindrically-symmetric flow travels to the axis of symmetry through a gas of uniform initial density ₀ and zero-pressure. A comparative study has been made between the results obtained in ordinary gasdynamics and magnetogasdynamics with transverse and axial components of the magnetic field. The value of similarity exponent has been assigned from that found in the paper of Whitham (1958).     

Effect of overtaking disturbances on a strong cylindrical hydromagnetic shock wave in a self-gravitating gas

The effect of overtaking disturbances upon the free propagation of strong cylindrical hydromagnetic shock through a self-gravitating gas has been studied by an approximating technique developed by Yadav. Assuming an initial density distribution law as ₀=r^–w, where is the density at the axis of symmetry and is a constant, the analytical relation for shock velocity and shock strength modified by overtaking waves has been obtained under two conditions: viz., (i) when the applied axial magnetic field is strong and (ii) when the field is weak. The results obtained here are compared with those for a freely propagating shock. The conclusions arrived at agreed with experimental results.It is shown that the applications of the CCW method and the neglect of overtaking disturbances are equivalent.     

Plane relativistic shock waves at the edge of a gas

Similarity solutions for propagation of plane relativistic shock waves through a medium of decreasing nucleon density and approaching the edge of the gas as well as for the subsequent motion of the gas after the shock front arrives at the vacuous boundary are studied in this paper. The medium in the pre-disturbed stage is assumed cold and in the disturbed stage its equation of state is taken as that of a photonic gas.     

Analytical solutions of cylindrical shock waves in magnetogasdynamics,I

The C.C.W. method has been used to investigate the propagation of converging and diverging cylindrical shock waves in a non-uniform medium under the influence of a magnetic field of constant strength. A comparison has also been made between the two types of cylindrical shock waves, simultaneously for both weak and strong cases of the magnetic field. Density distribution is assumed to be _o = r ^–, where is the density at the axis of symmetry and a constant. The analytical expressions for shock velocity and shock strength as well as the pressure, the density, and the particle velocity just behind the shock front have been derived for both the cases.     

Strong cylindrical magnetogasdynamic shock waves in a rotating interplanetary medium

Strong cylindrical magnetogasdynamic shock waves in rotating interplanetary medium has been studied and an analytic solution for their propagation has been obtained. Using characteristic method and considering the effect of Coriolis force, we have shown that magnetic field has significant effect on the velocity of the shock wave.     

Multisatellite observations of resonant hydromagnetic waves

Most measurements of long period ULF pulsations have come from ground based and single satellite observations. The observations have given strong support to the idea that these waves are resonant standing hydromagnetic waves on geomagnetic field lines. Simultaneous ground-satellite observations provide further details of the pulsation structure and are useful for examining the effect of the ionosphere on the transmission of the waves to the ground. Recently, multisatellite observations have been used to provide further insight into the nature of pulsations and we review the results obtained using this technique. Among the results presented are those from the ISEE 1 and 2 spacecraft which are closely spaced in identical orbits, making it possible to distinguish temporal from spatial structure in waves. The ISEE spacecraft have made measurements of resonant region widths and resonance harmonics. In addition, examples are shown of recent multisatellite observations of the global nature of some pulsations and the localization of Pi2 pulsations in space.     

Thermal overstability of hydromagnetic surface waves

We investigate the effects of radiative heat losses and thermal conductivity on the hydromagnetic surface waves along a magnetic discontinuity in a plasma of infinite electrical conductivity. We show that the effects of radiative heat losses on such surface waves are appreciable only when values of the plasma pressure on the two sides of the discontinuity are substantially different. Overstability of a surface wave requires that the medium in which it gives larger first-order compression should satisfy the criterion of Field (1965). Possible applications of the study to magnetic discontinuities in solar corona are briefly discussed.Collaborative programme in Astronomy and Astrophysics, Department of Physics, Indian Institute of Science, Bangalore 560012, India.     

Compressibility effects on hydromagnetic surface waves

The dispersion equation for hydromagnetic surface waves along a plasma-plasma interface has been solved as a function of the compressibility factor c ₁/v _A1, where c ₁ and v _A1 are the acoustic and Alfvén wave speed in one of the medium, for general wave propagation direction. Both slow and fast magnetosonic surface waves can exist. The nature and existence of these waves depends on the values of c ₁/v _A1 and , the angle of wave propagation. For low- plasmas only fast mode exists. The slow mode does not propagate below a critical value of c ₁. When c ₁ the phase velocity of the slow wave tend to the Alfvén surface wave velocity in the incompressible media and for large the phase velocity of the fast wave approaches this value. The phase velocity of the slow wave increases whereas for the fast wave it decreases with increase in the angle .     

A study of self-similar cylindrical MHD shock waves in monochromatic radiation

It is never too strange to expect that an eventual fifth repulsive interaction may also be mediated by a spin-2 field. On the other hand, it is highly unlikely that a spin-1 field may mediate an attractive force.     

Propagation of cylindrical shock waves under the action of monochromatic radiation

A model of cylindrical shock waves is investigated under the action of monochromatic radiation into non-uniform stellar interiors with a constant intensity on a unit area. We have assumed that the radiation flux moves through the gas.     

Non-similarity solutions for cylindrical shock waves in radiative magnetogasdynamics,I

The propagation of radiative-magnetogasdynamic cylindrical shock waves in an exponentially increasing medium is investigated. The shock wave moves with variable velocity and the total energy of the wave is also variable. The transformations in terms of , as given in the text, is necessarily a non-similarity one.     

Simultaneous geomagnetic and ionospheric oscillations caused by hydromagnetic waves

During magnetically quiet or slightly disturbed nights, closely correlated oscillations of the geomagnetic field and the F-layer were observed by means of magnetometers and a vertical-icidence continuous-wave Doppler sounder at 3.57 MHz. The magnetic oscillations were mostly Pi2 pulsations with periods from 0.5 to 2 min, and an amplitude of 10^?9 T corresponding to a Doppler shift of the order of 0.3 Hz. The observations cannot be explained by a dynamo-motor hypothesis assuming that the magnetic and ionospheric oscillations are caused by alternating E-layer currents, but they agree well with the theory of downgoing hydromagnetic waves. In particular, this theory explains the observed effects due to sporadic E-layer ionization and ion-neutral collisions. The results are found to differ substantially from those of other authors.