A search for helium ions in the recovery phase of a magnetic storm

Data from an energetic ion mass spectrometer experiment on the low-altitude polar-orbiting satellite 1971-89A were examined for evidence of helium ions in the region of the ring current during the recovery phase of the December 17–18, 1971, magnetic storm. The principal precipitating ion species with energies between 0.7 and 12 keV were observed to be O+ and H+. No evidence for He+ was obtained. Inferences about the composition of the trapped population are made on the basis of simultaneous observations in the equatorial plane by Explorer 45. Coordinated observations with Explorer 45 and the Fritz Peak Observatory during the period of a stable auroral red arc have provided some information on the ionospheric and magnetospheric processes associated with the arc. A comparison of charge exchange and precipitation lifetimes during the recovery phase of the December 17–18 storm has shown both processes to be of comparable importance as ring current decay mechanisms in the energy range of the observations.