The ionospheric contribution to the plasma environment in near-earth space

SCATHA and ISEE 1 satellite ion mass spectrometer data on ion composition near GEO are reviewed. The data were gathered during and close to magnetic storm activity to assess the characteristics of ion composition variations in order to predict the effects of hot GEO plasma on spacecraft instruments. Attention is given to both substorms and storms, the former being associated, at high latitudes, with auroral activity, the latter with ring currents. The ionosphere was found to supply hot H(+), O(+) and He(+) ions to the GEO magnetosphere, while the solar wind carried H(+) and He(+) ions. The ionosphere was the dominant source in both quiet and storm conditions in the inner magnetosphere.