Fast magnetic field‐line merging at the magnetospheric bow and in the tail are examined to determine their implications in regard to the concept of bulk motion of the magnetosphere (convection) and the associated electric field. Upper atmosphere geophysical measurements are surveyed to determine to what extent the available data support this concept. The dawn‐dusk asymmetry in energetic particle fluxes, the movement of auroral ionization, ionospheric currents, and the location of the whistler knee (or ‘plasmapause’) are all consistent with this concept, the latter three all giving estimates of the electrostatic potential difference across the magnetosphere in the dawn‐dusk meridian of a few tens of kilovolts. A ‘present best estimate’ of the flow pattern in the magnetosphere is derived, based primarily on the diurnal variation in the location of the whistler knee. The convective flow in from the tail appears to be stronger before midnight than after, which is consistent with the location of the maximum nighttime precipitation of energetic electrons. The derived flow is also qualitatively in agreement with that deduced from field‐line merging. However, the Axford‐Hines types of viscous drag will also give rise to convective flow, and the currently available data do not allow a definitive determination of whether field‐line merging or viscous interaction is the principal driving force.

A simple concise formulation of the problem of propagation in multicomponent plasmas with static magnetic fields is given. Application to plasmas, such as the ionosphere, containing electrons and multiple positive ions is considered. For each ionic species beyond the first, a multiple-ion resonance and a multiple-ion cutoff frequency are found for propagation perpendicular to the static magnetic field as well as a cutoff and the expected ion gyrofrequency resonance for the left circularly polarized (Alfv•n) mode. Also, for each additional ion a crossover frequency is found for which the two longitudinally propagating modes and the transverse extraordinary mode have the same phase velocity. If a crossover frequency moves through the frequency of a wave propagating in a slowly varying medium, the polarization of the wave is changed from predominately right circular to left circular or vice versa.

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The transfer of energy between whistler‐mode signals and energetic charged particles is examined. Resonance conditions are derived, leading to a classification of the mechanisms previously suggested for the generation of VLF emissions. The relationship between change in energy and change in pitch angle of the particles is derived for the transverse resonance interaction with longitudinal whistler‐mode waves. Features of the transverse resonance plasma instabilities and the anomalous Doppler effect are clarified.

An experimental study of the proton whistler, a new VLF phenomenon observed in satellite data, is presented, and an explanation of this new effect is given. The proton whistler appears on a frequency‐time spectrogram as a tone which starts immediately after the reception of a short fractional‐hop whistler at the satellite and initially shows a rapid rise in frequency, asymptotically approaching the gyrofrequency for protons in the plasma surrounding the satellite. It is proposed that the proton whistler is simply a dispersed form of the original lightning impulse and that the dispersion can be explained by considering the effect of ions on the propagation of an electromagnetic wave in the ionosphere. The propagation of a wave in a multicomponent plasma for frequencies of the order of the ion gyrofrequencies is discussed. In the ionosphere it is found that, in addition to the right‐hand polarized whistler mode, the left‐hand polarized mode (ion cyclotron wave) is also a possible mode of propagation for certain ranges of frequencies and altitudes. Between each two adjacent ion gyrofrequencies there is a frequency for which both modes of propagation are linearly polarized. These frequencies are called the crossover frequencies. A wave propagating in the ionosphere changes polarization at the altitude where the wave frequency is equal to a crossover frequency. This polarization reversal provides the mechanism by which an upgoing whistler can become an ion cyclotron wave. We show that the proton whistler is an ion cyclotron wave which occurs via this polarization reversal process. The crossover frequency can be measured from spectrograms of proton whistlers and is used to determine the fractional concentration of H+ in the plasma surrounding the satellite. Near the altitude and frequencies for which polarization reversal occurs, it is shown that the right‐hand polarized wave and the ion cyclotron wave may be strongly coupled. For frequencies of the order of the ion gyrofrequencies, this coupling process plays an important part in determining what regions of the ionosphere are accessible to waves from a given source location.