The Alfvén wave equation for magnetospheric plasmas
Abstract
It is shown that besides the continuous spectrum which damps away as inverse power of time, the coupled Alfvén wave equation, which gives coupling between a shear Alfvén wave and a surface wave, can also admit a well behaved harmonic solution in the closed form for a set of initial conditions. This solution, though valid for finite time intervals, points out that the Alfvén surface waves can have a band of frequency (instead of a monochromatic frequency for a nonsheared magnetic field) within which the local field line resonance frequency can lie, and thus can excite magnetic pulsations with latitudedependent frequency. By considering magnetic fields not only varying in magnitude but also in direction, it is shown that the time interval for the validity of the harmonic solution depend upon the angle between the magnetic field directions on either side of the magnetopause. For small values of the angle the time interval can become appreciably large.
 Publication:

Journal of Geophysical Research
 Pub Date:
 January 1988
 DOI:
 10.1029/JA093iA01p00295
 Bibcode:
 1988JGR....93..295U
 Keywords:

 Geomagnetism;
 KelvinHelmholtz Instability;
 Magnetohydrodynamic Waves;
 Magnetopause;
 Surface Waves;
 Wave Equations;
 Magnetic Fields;
 Resonant Frequencies;
 Solar Wind Velocity;
 Geophysics;
 Magnetospheric Physics: MHD waves and instabilities;
 Magnetospheric Physics: Magnetopause;
 cusp;
 and boundary layers;
 Magnetospheric Physics: Planetary magnetospheres;
 Magnetospheric Physics: Plasma waves and instabilities