Direct measurements bearing on the extent of thermal nonequilibrium in the ionosphere

Two ejectable instrument packages, consisting of a spherical ion trap and a cylindrical electrostatic probe, were flown above Eglin Air Force Base, Florida. The first was launched near midday local time on August 3, 1962, and the second was launched at mid-night October 24, 1962. The experimental technique is briefly reviewed. The major steps in the derivation of the equations for the ion current to a moving spherical ion trap are given, and the assumptions used in obtaining these equations are discussed. The daytime ion temperature profile derived directly from the ion. trap displays isothermal characteristics from 180 km up to 365 km, the apogee of the flight. This directly measured value of 1500°K compares reasonably well with the ion temperature value of 1650°K derived from the scale height of measured ion density. Electron temperature obtained from both the cylindrical probe and the ion trap showed a monotonie increase with altitude. The electron temperature measured at the apogee of the flight, 2750°K, indicates a high degree of thermal nonequilibrium. There is extremely good agreement between the electron temperature profiles obtained by the two methods. The nighttime electron temperature results also showed excellent agreement. The midnight electron temperature was 1000°K and isothermal from 150 km to 488 km, the apogee of the flight. No direct ion temperature information was obtained from the night flight; however, when we used the ion density results, the scale-height method indicated that the electrons and ions were essentially in thermal equilibrium. The results from these flights are compared with the results of other experiments and, from the daytime data, it is noted that the effects of an ionospheric storm on the electron temperature last longer than present-day theories would predict. The nighttime results indicate that a particle flux may play an important role in the heating of the ionosphere at night.