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Daytime electron density profiles measured at Fort Churchill have been found to be similar to those observed at White Sands. One winter nighttime flight showed very little ionization, less than 20,000 electrons per cc up to 165 km. Polar blackout produced strong enhancement of the D-region electron density down to 55 km. NO+ is the predominant ion below 200 km during the night, but O+ becomes the most abundant ion above 150 km during the day. Solar flares are accompanied by X-ray bursts capable of penetrating to the 60-km level and sufficiently intense to account for sudden ionospheric disturbances. At night a diffuse glow of Lyman-Â¿ is visible over the entire sky. From the observed intensity it is possible to estimate the electron density of interplanetary space.