METAL-ION LAYERS IN THE AURORAL LOWER E-REGION MEASURED BY MASS SPECTROMETERS

Within the Rocket and Scatter Experiments (ROSE) campaign the positive ion composition of the lower auroral E-region was probed by rocket-borne mass spectrometers in the altitude region from about 80 to 120 km. In all four flights with nearly identical geophysical conditions, that is, relatively high electric fields and sporadic-E layers, metal ions were found between 80 and 100 km altitude. The isotopic composition of the metal ions does not contradict a meteoric origin. The elemental composition indicates an enhancement of Fe+ over other metal ions, with respect to the solar system abundances, which cannot be explained by a different chemical behaviour. Column densities of iron atoms inferred from measured ion densities by chemical modelling essentially agree with observations made by the lidar technique. In one of the flights an intense thin layer was found at 91 km superimposed on the normal metal ion layer. The half-width of the thin layer was less than 1 km, while metal ion densities were enhanced by about one order of magnitude. The thin layer is supposed to be a sporadic-E event. Metallic ions detected are Na+, Mg+, Al+, Ca+, Cr+, Fe+, Ni+, FeO+ and possibly K+.