The effect of density inhomogeneity on standing Alfven wave structure

Abstract

At geomagnetic latitudes well within the plasmasphere (~25°–40°), ionospheric O + ions have a significant effect on hydromagnetic wave frequencies, waveforms and wave mode coupling. We apply a physically realistic plasmasphere model to obtain the eigenfunctions of the toroidal mode standing waves in a dipole field. Ion mass density inhomogeneities along the field lines (e.g. ionospheric O +, hemispheric asymmetry, or equatorial enhancements) result in a confinement of the wave fields within any significant density increase. Near latitude 30° the fundamental toroidal mode electric field has its largest values well away from the equatorial plane. The effects of the ionospheric F-region need to be considered when mapping pulsation fields and evaluating hydromagnetic wave coupling at low latitudes. The irregular spacing of the toroidal mode harmonic frequencies near latitude 30° is a direct consequence of the Alfvén velocity inhomogeneity over a substantial portion of the field line length.