Discovery of energetic molecular ions (NO⁺ and O₂⁺) in the storm time ring current

A few hours after the onset of a large geomagnetic storm on September 4, 1984, energetic molecular ions in the mass range 28‐32, predominantly NO + and O 2 + , have been discovered in the outer ring current at L ∼ 7. The data have been obtained with the time‐of‐flight spectrometer SULEICA on the AMPTE/IRM spacecraft. We find at 160 keV/e a mean abundance ratio of the molecular ions relative to O + ions of 0.031±0.004. During quiet times no molecular ions are observed, the 1 σ upper limit of the ratio derived by averaging over several quiet periods is 0.003. The observations demonstrate the injection of ionospheric plasma into the storm time ring current and the subsequent acceleration to energies of several hundred keV on a time scale of a few hours after the onset of the magnetic storm.