Magnetohydrodynamic Wave Modes Research Articles

Magnetohydrodynamic wave mode conversion in the Earth's magnetotail

We study magnetohydrodynamic wave mode conversion as a mechanism contributing to the observed low‐frequency electromagnetic fluctuation level in the plasma sheet. Low‐frequency waves originating in the magnetosheath can transport energy across the tail flank magnetopause and through the tail lobes toward the plasma sheet. In the plasma sheet boundary layer and in the central plasma sheet, local conditions permit mode conversion to occur in resonant sheets. Resonant coupling to both Alfvén and slow‐mode waves is possible. Energy is fed to the plasma in these resonant sheets, which may help to explain the acceleration and heating of particles observed in the plasma sheet boundary layer and the central plasma sheet.

Standing magnetohydrodynamic wave modes in a viscous, gravitationally stratified cylindrical plasma

Abstract We consider standing wave solutions of the linearized magnetohydrodynamic (MHD) equations describing a perfectly conducting but viscous magnetofluid in a gravitationally-stratified cylindrical plasma. We assume a relatively strong homogeneous background magnetic field within the flux tube, which is oriented along the cylinder axis; the background atmosphere is in hydrostatic equilibrium, with gravity uniform and parallel to the cylinder axis; the vertical temperature profile (constrained by the stability conditions) is arbitrary. The MHD wave equations are separable, and appropriate boundary conditions are formulated. We employ a numerical shooting scheme to solve the coupled ordinary differential equations and to obtain the damping rates and eigenfrequency spectra for the standing MHD wave modes. Three series of modes are obtained for an isothermal flux tube: Alfvtnic, quasi-fast, and quasi-slow. The quasi-slow mode series is novel, having been missed previously. In the inviscid limit, with a st...

Electron heating by fast mode magnetohydrodynamic waves in the solar wind emanating from coronal holes

It is shown that fast mode magnetohydrodynamic waves, propagating outwards from the sun in coronal hole regions, will dissipate primarily through collisionless interaction with electrons rather than with protons. This dissipation can lead to higher electron than proton temperatures in the accelerating region of the solar wind, provided the waves carry a sufficiently large energy flux.

Numerical experimentation on spherically symmetric one-dimensional magnetohydrodynamic (MHD) wave propagation

Radial propagation of one-dimensional magnetohydrodynamic (MHD) waves are analyzed numerically on the basis of the Implicit-Continuous-Fluid-Eulerian (ICE) scheme. Accuracy of the numerical method and other properties are tested through the study of MHD wave propagation. The three different modes of MHD waves (i.e. fast- slow- and Alfven (transverse) mode) are generated by applying physically consistent boundary perturbations derived from MHD compatibility relations. It is shown that the resulting flow following these waves depend upon the relative configurations of the initial magnetic field and boundary perturbations.

On the acoustic and magnetoacoustic heating of the outer atmosphere of stars

Observational and theoretical evidence indicates that chromospheres are very likely heated by acoustic and by slow mode magnetohydrodynamic waves. The acoustic heating of coronae which has recently been disclaimed still appears to be an important possibility.

Modes of magnetohydrodynamic waves in the magnetosphere

Magnetohydrodynamic plasma waves (waves with frequencies less than the local ion gyrofrequency) constitute an important part of the wave frequency spectrum in the earth's magnetosphere and in the solar wind. Such plasma waves also probably play an important role in astrophysical plasmas. The nature and modes of the plasma waves excited in the earth’s magnetosphere are of interest because they are generated and propagate in a plasma environment imbedded in a dipole magnetic field configuration. As such, analyses of the nature of these waves may prove useful in studies of some planetary and stellar plasma environments. Measurements made at conjugate points on the earth's surface and in the magnetosphere between spacecraft altitudes and the ground provide information on the nature of the modes of the magnetohydrodynamic waves excited in the magnetosphere. This paper reviews the available data on wave modes and concludes that near L=4 (corresponding to geomagnetic latitudes ∼60°) the mode for waves in the period range ∼20 to ∼200 s is predominantly odd mode. This may be a fundamental aspect of the physical process that couples the driving source to the resonant field line. For other geomagnetic and frequency ranges there is presently a disappointing dearth of experimental observations.

The interaction of homogeneous wave turbulence and a magnetohydrodynamic tangential discontinuity

The interaction of homogeneous wave turbulence and a magnetohydrodynamic tangential discontinuity is studied. Attention is focused on the turbulent shear stress produced as a result of such an interaction. A magnetohydrodynamic description is used which is believed to be adequate for plasma problems in interplanetary space. As a model for wave turbulence, it is assumed that the turbulent wave field is made up of the seven modes of magnetohydrodynamic waves. They are the entropy waves, the Alfvn waves (two independent modes), the fast and slow waves (each with two independent modes). It is found that to a first approximation the turbulent shear stress acting on the surface of discontinuity is linearly proportional to the energy density of the fluctuating magnetic field and to the kinetic energy density of the plasma fluctuations. On applying the present theory to the problem of interaction between the turbulent waves in the magnetosheath and the magnetopause, it is found that the turbulent shear stress produced is too weak to produce any large-scale internal magnetospheric convection as was previously contemplated.

Magnetohydrodynamic Wave Modes behind Normal Ionizing Shock Waves

The distribution of current loops that develop behind strong ionizing shock waves in a coxial electromagnetic tube has been studied experimentally and found to be similar to modes excited by two dimensional magnetohydrodynamic waves.