Propagation Of Hydromagnetic Waves Research Articles

Propagation of Weak Hydromagnetic Shock Waves in the Exosphere and Geomagnetic Variations Due to High Altitude Nuclear Explosion

Propagation paths are calculated for weak hydromagnetic shock waves (fast mode) from a point source lower than 3000km above the sea level. It is shown that the shock waves of this type have a tendency to propagate easily in the direction of the geomagnetic meridian. The results are compared with the observed geomagnetic disturbances due to the small scale high altitude nuclear explosion (Argus III). A qualitative agreement is obtained between the theoretical and the observational results.

On the interpretation of the sudden commencement of geomagnetic storms

The propagation and geometric attenuation of hydromagnetic waves in the earth's magnetic field are calculated by the methods of geometrical optics. The waves are assumed to be generated by point sources located at a distance of 6 earth radii from the center of the earth. It is shown that the ray tracing method cannot be used to explain the rise time of sudden commencements of geomagnetic storms. However, the calculated propagation times of hydromagnetic disturbances can give an understanding of delay times and latitude dependence of arrival times. If extended sources are considered, the following conclusion results from our analysis: According to geometric optics, hydromagnetic disturbances of the fast mode produced at 6 earth radii by the interaction of a solar plasma front with the earth's magnetosphere will reach the earth only if they are produced in a region within a radius of a few thousand kilometers of the subsolar point.

Hydromagnetic Wave Propagation near Ion Cyclotron Resonance

A torsional hydromagnetic wave is induced by application of an oscillatory radial electric field to one end of a cylindrical deuterium plasma located in a magnetic mirror field. The wave propagates in the axial direction to the center of the device, where a resonance occurs between the hydromagnetic wave frequency and the local ion cyclotron frequency. Wave magnetic-field measurements indicate that transfer of power from the 1-MW, 8.3-Mc oscillator to the hydromagnetic wave is about 65% efficient, and that more than 90% of the wave energy is transferred out of the wave at the resonance region.

The effect of finite conductivity on the propagation of hydromagnetic slow waves

The present paper deals with the one-dimensional propagation of disturbances in an inviscid conducting fluid of finite magnetic Reynolds number. The following conspicuous property is shown: The basic equations are not hyperbolic but nevertheless the slow wave has a domain of dependence determined by the sound velocity.

Distant electromagnetic observations of the high-altitude nuclear detonation of July 9, 1962

After the Argus experiment of late summer 1958, Porter [1959], Newman [1959], and Selzer [1959] reported the detection of ELF magnetic signals at substantial angular displacement and at considerable distance from the magnetic meridian of the Argus explosions. These observations were subsequently confirmed at various French magnetic stations by Eschenbrenner et al. [1960] and Launay and Beccaria [1960], and the published data were applied to construction of a hydromagnetic wave propagation pattern by Berthold, Hams, and Hope [I960]. No direct detection of VLF signals was reported by any of these authors. The high-altitude thermonuclear explosion over Johnston Island in the Pacific on July 9, 1962, again generated magnetic effects far from the explosion meridian. This note presents and summarizes data obtained after the July 9 test at an observing site near Los Angeles, where both VLF and ELF signals of large amplitude were recorded.

Propagation of hydromagnetic waves in the lower exosphere and the origin of short period geomagnetic pulsations

The exospheric region below an altitude of about 2000 km, where the Alfvén velocity has a very steep upward gradient, amplifies hydromagnetic waves coming from outer space with certain special periods. The longest characteristic period, corresponding to the fundamental mode, is of the order of from 1 to several seconds, which is comparable to the period of that particular group of geomagnetic micropulsations called pearls. The fundamental period has a frequency-width of the order of 0.02–0.08 sec −1 which is of the right order of the time-scale of fluctuations of the envelope of the pearls. The amplifying ratio also gives the correct order of magnitude of the intensity of pearls as observed at the earth's surface.

Supernovae as Cosmic-Ray Sources

Certain characteristics of supernovae, inferred from observations and theories, are interpreted as suggesting that the young remnants of a supernovae eruption constitute a powerful source of cosmic rays. These features include an enormous energy release, a copious supply of relativistic electrons, large-scale magnetic fields, extended masses of plasma moving at high velocities, indications of the propagation of hydromagnetic waves, and relatively high concentrations of heavier elements. Recent evidence is reviewed which was obtained by the analysis of the continuous spectrum of electromagnetic radiations from the Crab Nebula, optical and nonthermal radio emissions, and photoelectric and photographic techniques employing polaroid filters. Notation, constants, and conversion factors used in the calculations are included. (Seventy-three references.) (C.H.)

On the Isotropic Hydromagnetic Waves in the Exosphere

We study in this paper the propagation of weak hydromagnetic waves in the exosphere between 1×103Km and 5×104Km height levels from the Earth's surface, based on simplified models. In the upper atmosphere the steady magnetic field is a dipole one, and it is, in general, difficult to discuss the wave propagation in such a field. But, in some special regions, an approximate treatment can be permitted. An attempt is made to describe two-dimensional wave fronts in the regions near the geomagnetic equatorial plane and high above the geomagnetic pole, using an approximate height-variation of the Alfvén wave velocity, and it is found that: (1) For our isotropic wave, the shape of wave fronts is the same for both the equatorial region and the polar one. (2) In the upper region above Va (Alfvén wave velocity) maximum height level the incident waves with large pitch angle to the zenith are almost reflected, and on the contrary, in the region below Va maximum height level the incident waves with any pitch angle have tendency propagating almost the Earth-ward.

On the Reflection and Refraction of Hydromagnetic Waves in Ionized Gas II

We are interested in the manner of propagation of hydromagnetic waves in the Earth's upper atmosphere. The density changes continuously in the atmosphere and the steady magnetic field is a dipole field, but we discuss here the laws of reflection and refraction of hydromagnetic waves at a plane boundary between two semi-infinite homogeneous media of anisotropic electrical conductivity under a uniform steady magnetic field. When the steady magnetic field is perpendicular to the boundary plane, the laws of reflection and refraction are simple, but when the steady magnetic field makes an angle with the plane, they are complicated. The incident ordinary (or extraordinary) waves may be reflected or refracted as the ordinary or extraordinary waves and propagate anisotropically.

Spectrum of hydromagnetic waves in the exosphere

A disturbance in the exosphere generates waves in three partially separable modes. The modes are described by considering the vorticity about a line of force, the two-dimensional divergences of velocity in the plane perpendicular to the line of force, and the component of velocity along the line of force. The propagation of vorticity is one-dimensional and there is no geometrical attenuation. It is suggested that this mode is associated with the sudden commencement of a magnetic storm. The propagation of the longitudinal component velocity is almost one-dimensional, but it is heavily damped at high frequencies. In a gravitational field, the medium is no longer uniform, and at low frequencies the modes are coupled in a complicated way. The influence of gravity is characterized by the frequency of oscillation of a small parcel of fluid when displaced from its zero-order position in the gravitational field. For parallel magnetic and gravitational fields the vorticity mode is still separable, and gravity leads to anisotropic dispersion in the other modes. The propagation at low frequencies is no longer cylindrically symmetrical if the lines of force are at an arbitrary angle to the direction of gravity. Detailed investigations of the influence of the gravitational field on hydromagnetic wave propagation is carried out for the case where the sound velocity is small compared to the Alfven wave velocity. The principal aim of the study is an attempt to provide a background for the separation of source effects from those of the medium as an aid to the spectral study of magnetic records. The relative proportion of the three modes generated by a specific source is estimated. Consideration of the regions of allowed solutions in frequency-wave number space show that the vorticity mode will have a narrow spectrum. It is suggested that high-frequency micropulsations are associated with vorticity mode propagation. Examples of vorticity generating sources include the turbulent region in the vicinity of a finite amplitude wave, the outgassing of a rocket motor, and a wake of a satellite in the lower exosphere. Energy may be trapped within the exosphere in various free vorticity mode oscillations. The free periods of these oscillations are comparable to the periods observed in the low frequency micropulsations. The limiting conditions for the propagation of the various modes in the exosphere are considered. Because of the long-range nature of the Coulomb forces, the charged particle may travel distances short compared with its mean free path and still exchange a substantial proportion of its momentum. For representative models of the exosphere, disturbances at several earth radii must have a length scale large compared with several kilometers for the propagation of the longitudinal component of velocity. The limiting conditions on the vorticity and transverse modes involve the ratio of the length scale of the disturbance to the Larmor radius. These modes are propagated if the disturbances have length scales of some hundreds of meters in the outer regions of the exosphere.

Electro-hydromagnetic waves in a fully ionized gas-II

The propagation of hydromagnetic and low frequency radio waves in all directions in a fully ionized gas containing a magnetic field is examined. For longitudinal and transverse propagation the addition of one extra term in the magneto-ionic formulae (without collisions) accounts for the presence of heavy ions. The partition of energy of disturbance between kinetic ( K) and magnetic ( M) for longitudinal propagation of all frequencies is given by K=V 2 k 2 σ 2 M 1− σ 2 k 2c 2 2 where V is the Alfvén speed. Thus approximate equipartition may exist for some audio- and radio-frequencies in the Earth's exosphere. Some errors in Paper I of this series are corrected.

On The Reflection and Refraction of Hydromagnetic Waves in Ionised Gas

We are interested in the manner of propagation of hydromagnetic waves in the Earth's upper atmosphere. The density changes continuously in the atmosphere and the steady magnetic field is a dipole field, but we discuss here the laws of reflection and refraction of hydromagnetic waves at a plane boundary between two semi-infinite homogeneous media of anisotropic electrical conductivity under a uniform steady magnetic field. When the steady magnetic field is perpendicular to the boundary plane, the laws of reflection and refraction are simple, but when the steady magnetic field makes an angle with the plane, they are complicated. The incident ordinary (or extraordinary) waves may be reflected or refracted as the ordinary or extraordinary waves and propagate anisotropically.

Evidence of Quasi-Perpendicular Propagation of Hydromagnetic Waves caused by Nuclear Explosions over Johnston Island

IN previous reports1,2 one of us (H. M.) has suggested that the initial phase of artificial magnetic storms due to high-altitude nuclear explosions over Johnston Island (16.5° N.; 169.5° W.) may be interpreted by hydromagnetic waves propagated through the high atmosphere from the explosion point. Such a suggestion has also been made by many other workers. The purpose of this communication is to exhibit evidence supporting such a suggestion. (Quite recently, Berthold et al. 3 have also found similar effects due to Argus.)

On the Theory of Propagation and Decay of Hydromagnetic Waves in an Anisotropic Medium

On the Theory of Propagation and Decay of Hydromagnetic Waves in an Anisotropic Medium

Hydromagnetic wave propagation in the ionosphere

The dispersion equation of hydromagnetic waves, including the effects of collisions, is obtained for an arbitrary angle between the direction of propagation and the direction of a primary magnetic field, assuming certain approximations usually valid in the terrestrial ionosphere. Special cases of the general dispersion equation are considered and some well-known results are regained. Expressions for the dissipated power are derived. The propagation of hydromagnetic waves in a horizontally-stratified ionosphere is discussed, by analogy with the propagation of very-low-frequency radio waves.

The Impact of the Argus Experiment on Hydromagnetic-Wave Research

The Argus series of high-altitude nuclear explosions has provided us with the means of studying hydromagnetic-wave effects under known and controllable conditions. These explosions have enabled us to compare, for the first time, quantitative experimental data with theoretical considerations. Analysis of the world-wide hydromagnetic-wave effects led to the discovery of an interesting duct-like mechanism for the propagation of hydromagnetic waves at altitudes between 2000 and 3000 km. This mechanism is essential for the efficient propagation of hydromagnetic waves over global distances.

Electro-hydromagnetic waves in a fully ionized gas—I

Transport equations are used to determine coefficients which are generalizations for any frequency of electric field of the parallel, Pedersen and Hall conductivities in a fully ionized gas. These coefficients are used in an investigation of the propagation of weak electromagnetic and hydromagnetic waves of all frequencies across a homogeneous and constant magnetic field in a rarefied fully ionized gas. For propagation perpendicular to the magnetic field it is found for all frequencies i σ 2 K 2 =C 2 τ V 2 C 2 σ P 2−σ 2 +σ τ(σ P 2−σ 2)+iσ ii 1 2 ρ|υ| 2=V 2· |k| 2 σ 2 · |h| 2 8π where V 2 = H 2/4 πϱ and v, h are the perturbations of the velocity, magnetic field. Similar relationships are deduced for propagation at any angle to the field for frequencies greater than about 10 times the gyrofrequency of electrons. The theory is applied to discuss transmission of disturbance across the interplanetary medium, the temperature of the solar corona and the earth's outer atmosphere, the emission of non-thermal solar radio noise, cosmic radio noise and the anomalous emission of light from shock fronts.

The Propagation of Hydromagnetic Waves of Finite Amplitude in a Horizontally Stratified Atmosphere.

view Abstract Citations References (4) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Propagation of Hydromagnetic Waves of Finite Amplitude in a Horizontally Stratified Atmosphere. Plumpton, C. Abstract e vertical propagation of a train of transverse harmonic hydromagnetic waves of finite amplitude in the presence of a uniform vertical magnetic field is discussed. It is shown that, although in this case the motion of the gas cannot be wholly horizontal, the vertical motion is negligible so long as the particle velocity is small compared with the local sonic velocity. Approximate solutions of the field equations are derived, and the results are discussed in relation to the propagation of waves in the solar atmosphere. Publication: The Astrophysical Journal Pub Date: May 1959 DOI: 10.1086/146672 Bibcode: 1959ApJ...129..752P full text sources ADS |

Interactions of Hydromagnetic Waves

A generalized Rankine-Hugoniot relation for hydromagnetic shock waves propagating perpendicularly to the magnetic field is discussed. Then the interaction of the shock or rarefaction waves with the contact surface on which the magnetic field has a discontinuity is, analyzed by a graphical method. The motion of the high temperature part of a plasma surrounded by the strong magnetic field and the electric current is investigated applying the result of the above analysis. It is shown that under some initial condition the contracting motion of the plasma occurs succeeding its expansion. The results obtained by them show that the propagation of shocks is generally complicated for the arbitrary configuration of the magnetic field. However, it was shown by Taniuti G ) that the analysis of the fluid with infinite conductivity can be comparatively simplified, and that the propagation of hydromagnetic waves may be described in the way analogous to that of the ordinary hydrodynamics so far as the one-dimensional propagation of the hydromagnetic wave perpendicular to the magnetic field is concerned. In the present article, we deal with these perpendicular shock and rarefaction waves and their interaction. In § 2, the various shock relations, involving an equation which corresponds to the Rankine-Hugoniot equation in the hydrodynamics, will be presented. 4 ) The analysis of the interaction between the shock, rarefaction wave and the contact discontinuity will be given in § 3. In § 4 we shall discuss, on the basis of these results, an initial value problem in which the fluid is initially at rest and the high density part of the fluid associated with a weak magnetic field is surrounded by the low density part with a strong magnetic field. The subsequent b~haviour of the fluid and the magnetic field will be calculated in detail and it will be pointed out that under certain conditions the contact surface can oscillate due to its interaction with the rarefaction and shock waves. We hope that this result concerning the motion of the contact surface may be of some use for the qualitative explanations of some experimental facts, resulting from the pinched discharge in the cylindrical tube, although it may be difficult to find any actual phenomenon exactly corresponding with this kind of initial value problem.

On the Reflection and Refraction of Alfven Waves.

view Abstract Citations (62) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Reflection and Refraction of Alfven Waves. Ferraro, V. C. A. Abstract It is shown that plane harmonic hydromagnetic waves polarized at right angles to the plane of incidence can be reflected and refracted from a plane surface of separation of two infinitely conducting liquids. The general laws of reflection and refraction are derived, and it is shown that these depend on the orientation of the permanent uniform magnetic field with respect to the surface of separation and the plane of incidence. The propagation of hydromagnetic waves in a horizontally stratified isothermal atmosphere lying over an infinitely conducting liquid is briefly discussed. It is shown that eventually the magnetic field associated with waves decreases with height proportionately to the density of the atmosphere. Publication: The Astrophysical Journal Pub Date: March 1954 DOI: 10.1086/145837 Bibcode: 1954ApJ...119..393F full text sources ADS |