Auroral zone ion composition

The paper discusses the auroral zone and its role as the region of exchange of warm and hot plasmas between the magetosphere and ionosphere. Consideration is then given to the ion mass, energy, and angle distributions observed on a typical midaltitude auroral zone crossing and the central role of oxygen ions as a tracer of the processes involved in the coupling of ionospheric and magnetospheric plasmas. The successful operation of the Swedish Viking satellite in 1986 is noted.