ABSTRACT
In the magnetosphere, the first studies of field-line resonance emphasized the behaviour of the fields near resonance. They were carried out when the most detailed experimental information was the magnetometer information showing a change of polarization at a critical latitude. The inherent resolution imposed on magnetometer data meant that the details of the resonance region were unresolved. The magnitude of the magnetic field and, thus, the Alfven speed increases inwards from the boundary. A wave incident from the magnetosheath is partly reflected and partly transmitted by the magnetopause. As the Alfven speed increases, the wave is refracted by the medium within the magnetosphere. The thickness of the magnetopause is small compared with the wavelength so that it can be treated as a discontinuity in the Magnetohydrodynamic medium. Across it, the density, pressure, magnetic field, and plasma velocity change.
