Temperature and density in the ionized upper atmosphere at 4000 to 5300 kilometers

Measurements of the ion density between 550 km and 5500 km made in 1960 have been given in a preliminary report by Hale and have been interpreted by Hanson. Hale's preliminary data indicated that the density began to increase with increasing altitude above 4200 km, but this fact was neither noted nor explained at that time. Laboratory calibrations and re-evaluation of the 1960 data initiated at North Carolina State in 1962 have been completed. They show that either the density increases more than fourfold between 4000 and 5500 km and is increasing rapidly at the upper value, or the temperature is greater than 32,000°K in this altitude range. Further measurements are needed to determine which interpretation is correct.