A reverse hydromagnetic shock in the solar wind
Reverse hydromagnetic shock in solar wind as discontinuity of plasma density, proton temperature and magnetic field density, using spacecraft data
Burlaga, L. F.↗
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Hydromagnetic waves and discontinuities in the solar wind
Hydromagnetic waves and discontinuities in solar wind
Burlaga, L. F.↗
Kelvin instability in a composite hydromagnetic system
Two component hydromagnetic system Kelvin instability due to tangential velocities discontinuity, using normal mode analysis
Talwar, S. P.↗
On hydromagnetic precession in a cylinder
Rotating fluid cylinder in magnetic field parallel to rotation axis, discussing hydromagnetic precession rate, resonance phenomena and magnetic Reynolds number flows
Gans, R. F.↗
Solar and lunar hydromagnetic tides in the earth's magnetosphere
Solar and lunar hydromagnetic tides in earth magnetosphere obtained from electrostatic fields in dynamo region
Maeda, H.↗
Propagation of hydromagnetic waves in a stochastic magnetic field
Coherent small amplitude hydromagnetic wave propagation in magnetic field with time independent random component
Valley, G. C.↗
On hydromagnetic oscillations in a rotating cavity.
Time-dependent hydromagnetic phenomena in a rotating spherical cavity are investigated in the framework of an interior boundary-layer expansion. The first type of wave is a modification of the hydrodynamic inertial wave, the second is a pseudo-geostrophic wave and is involved in spinup, and the third is related to the MAC waves of Braginskii (1967). It is shown that the MAC waves must satisfy more than the usual normal boundary conditions, and that reference must be made to the boundary-layer solution to resolve the ambiguity regarding which conditions are to be taken. The boundary-layer structure is investigated in detail to display the interactions between applied field, viscosity, electrical conductivity, frequency and latitu de.
Gans, R. F.↗
Plasma heating and acceleration due to Landau damping of hydromagnetic waves.
We analyze energy and momentum exchange associated with Landau damping of hydromagnetic waves, from a macroscopic viewpoint, and compare the conclusions with those of the resonant quasi-linear theory. It is found that the heating of protons and electrons is correctly given by the resonant theory, but that the momentum exchange is not correctly described by the resonant theory.
Barnes, A.↗
Hydrostatic equilibrium of hydromagnetic fields.
The condition for a hydromagnetic field to be in hydrostatic equilibrium is discussed. It is shown that if the topology of the wrapping pattern of lines of force of a non-force-free field around each other changes along the field, then the configuration cannot be in hydrostatic equilibrium. A general discussion is given, and several special cases are worked out to illustrate the general equilibrium requirement.
Yu, G.↗
Study of low frequency hydromagnetic waves using ATS-1 data
Summaries are presented on the use of ATS-1 data to analyze low frequency oscillations of the earth's magnetic field and hydromagnetic wave polarization.
Cummings, W. D.↗
Reflection and refraction of hydromagnetic waves at the magnetopause
Reflection and transmission coefficients of MHD waves are obtained at a stable, plane interface which separates two compressible, perfectly conducting media in relative motion to each other. The coefficients are evaluated for representative conditions of the quiet-time, near-earth magnetopause. The transmission coefficient averaged over a hemispherical distribution of incident waves is found to be 1-2%. Yet the magnitude of the energy flux deposited into the magnetosphere in a day averaged over a hemispherical distribution of waves having amplitudes of say 2-3 gamma, is estimated to be of the order 10 to the 22-nd power erg. Therefore the energy input of MHD waves must contribute significantly to the energy budget of the magnetosphere. The assumption that the boundary surface is a tangential discontinuity with no curvature limits the present theory to hydromagnetic frequencies higher than about .1 Hz.
Verzariu, P.↗
Large-amplitude hydromagnetic waves
Several aspects of the theory of large-amplitude hydromagnetic waves and their behavior in the interplanetary medium are examined. The characteristic modes of the full (i.e., nonlinearized) MHD equations and their modification by collisionless and finite-frequency effects are considered. Special attention is paid to the transverse Alfven mode, which is undamped and characterized by strictly constant pressure, density, and B; this seems to be the predominant propagating fluctuation at 1 AU. It is shown that its propagation in the small-wavelength (WKB) approximation is essentially identical to that of the small-amplitude Alfven wave of linearized theory. It is also suggested that its presence at 1 AU may provide a natural explanation of the observed power anisotropy of the fluctuations. A second-order analysis is used to study fluctuations that are not characteristic modes. It is found that for a small range of propagation directions, and subject to third-order effects, a finite-amplitude wave can exist that is linearly polarized with delta B perpendicular to both B sub zero and k; such a wave can damp nonlinearly.
Barnes, A.↗
Hydromagnetic waves guided by the geomagnetic field
Properties of hydromagnetic waves propagating in the magnetosphere from a source of limited dimensions are considered. It is shown that they are closely related to electric currents flowing along geomagnetic lines of force. The notions developed form a theoretical basis for interpretation of fluctuations and polar bays.
Vanyan, L. L.↗
Hydromagnetic waves and cosmic-ray diffusion theory
Pitch-angle (and energy) diffusion of cosmic rays in hydromagnetic wave fields is considered. The treatment remains strictly within the quasi-linear approximation. It is shown that the popular assumption of an isotropic power spectrum tensor of magnetic fluctuations requires in this case equal forms and magnitudes of Alfven and magnetosonic wave spectra - a situation which is generally unlikely. The relative contributions to the pitch-angle diffusion coefficient from the cyclotron resonances and Landau resonance due to the different types of waves are evaluated for a typical situation in the solar wind. Since the Landau resonance in this approximation also does not lead to particle reflections, a proper consideration of the nonlinear particle orbits is indeed necessary to overcome the well-known difficulties of quasi-linear scattering theory for cosmic rays near 90 deg pitch angle.
Lee, M. A.↗
Electromagnetic and hydromagnetic waves in a cold magnetoplasma
The basis of the theory of waves in a cold homogeneous magnetoplasma is reviewed. The radio approximation (associated with Appleton) applies when the wave-frequency is large compared with the geometric mean of the electronic and ionic gyrofrequencies. The hydromagnetic approximation (associated with Alfven) corresponds to infinite conductivity along the lines of flux of the imposed magnetic field and applies when the wave-frequency is small compared with the plasma-frequency. The rich variety of dispersion phenomena existing in a magnetoplasma is illustrated by polar diagrams showing both the variation of group-velocity with beam-direction and the direction in which the antenna must be pointed to aim a beam in a particular direction.
Booker, H. G.↗
Hydromagnetic waves and cosmic ray diffusion theory
Pitch angle diffusion of cosmic rays in hydromagnetic wave fields is considered strictly within the quasilinear approximation. It is shown that the popular assumption of an isotropic power spectrum tensor of magnetic fluctuations requires in this case equal forms and magnitudes of Alfven and magnetosonic wave spectra - a situation which is generally unlikely. The relative contributions to the pitch angle diffusion coefficient from the cyclotron resonances and Landau resonance due to the different types of waves are evaluated for a typical situation in the solar wind. Since in this approximation also the Landau resonance does not lead to particle reflections a proper consideration of the nonlinear particle orbits is indeed necessary to overcome the well known difficulties of quasilinear scattering theory for cosmic rays near 90 degrees pitch angle.
Lee, M. A.↗
Grain disruption in interstellar hydromagnetic shocks
The observed abundance variations of Ca, Fe, Si, and Ti in intermediate-velocity interstellar gas suggest that grains have been disrupted in clouds with velocities as low as 20 to 50 km/s. A simplified hydromagnetic shock model for such clouds is described; the dynamical equations for charged grains in the postshock region are derived, including the collisional drag and 'betatron-acceleration' effect of a magnetic-field gradient; and the fraction of grains destroyed in evaporative collisions with other grains is calculated. It is found that for shocks of 20 to 50 km/s in which the fractional H-ionization remains low, 3-10% of the grain material may be destroyed - sufficient to explain in part the heavy-element depletion pattern in intermediate velocity clouds and the well-known correlation of N(Ca II)/N(Na I) with cloud velocity.
Shull, J. M.↗
On the hydromagnetic model of comets
Several consequences of Alfven's (1957) hydromagnetic model of comets are developed. It is shown that such a model not only accounts for the observed morphology and time variations of the fine structure in the plasma tail, but also leads, in a natural way, towards explanations of two of the central problems in cometary physics; namely, the short ionization time-scales of the cometary molecules, and the large velocities and accelerations observed far down the tail.
Mendis, D. A.↗