On the plasma environment of solitary waves and weak double layers

Observations of charged particles during events of solitary waves and weak double layer‐like structures by the Swedish magnetospheric research satellite Viking are discussed. The observations took place in relatively weak acceleration regions at altitudes between 1 and 2 RE. The total accelerating potential was typically somewhat less than 1 kV. The characteristics of ion and electron spectra indicate that the main part of the potential was below the satellite but some field‐aligned acceleration of electrons had also taken place above it. The composition of the ion beams was dominated by protons with a variable concentration (0–30%) of oxygen ions. While it is difficult to determine the exact parameters of the background plasma, there is clear evidence of the presence of cool background electrons and ions. It is proposed that the weak double layer‐like structures are structures in the cool ambient ions and convect slowly upward with the ion population. On the other hand, the structures accelerate auroral electrons toward Earth and beam ions from the ionosphere upward. It is suggested that the structures are likely to contribute to the perpendicular heating of the ion beams.