Electrical processes in the nighttime exosphere

The results of nighttime measurements of positive ion densities between 240 and 1875 km are presented. The ion scale height is found to change abruptly around 600 km, increasing from 120 km at 500 km to 1400 at 640 km; it increases gradually with height above this level. An ion temperature of 1050±50°K is deduced from the ion scale height measured above the peak of the F region. The ion-density measurements were obtained by means of a spherical electrostatic analyzer flown on a Blue Scout rocket. In the altitude region 280 to 350 km the ion-density values agree to within 15 per cent with the electron-density measurements obtained from local ground-based ionosondes. The vertical distributions of the principal light ions above 400 km are calculated, assuming the existence of diffusive equilibrium. The relative abundance of the different ionic species at the reference level is determined from the measured profile of the total ion density. The results of the nighttime flight show that the atomic oxygen ion is the principal constituent below 530 km and ionized hydrogen the major constituent above 550 km. An upper limit is placed on the helium ion distribution, which attains its maximum value at 550 km. At this level it constitutes a maximum of about 7 per cent of the total ion density. The ion-atom interchange coefficient for the production of NO+ is calculated from the variations with time of charge densities in the altitude region 280 to 300 km; the coefficient is found to vary between 2 and 4 × 10−12 cm3 sec−1.