The ion chemistry and thermal balance of the E-and lower F-regions of the daytime ionosphere: An experimental study

Abstract

The processes of heating and ionization in the E- and F-regions of the daytime ionosphere are discussed in depth. Construction of a sounding-rocket payload, consisting of an assembly of extreme ultraviolet (EUV) spectrometers and plasma probes designed for simultaneous measurement of related ionospheric parameters, is described, and results obtained from a flight of this payload on a sun-pointing Skylark sounding rocket at Woomera, S. Australia (31°S, 137°E) on 3 April 1969 are presented in detail. The derivation of neutral atmosphere densities and temperatures from the spectrometer data is defined, and the values obtained for ion production rates due to the absorption of solar EUV radiation in the 100–270 km range presented. Based on these data, individual ion densities and the ambient electron temperature are calculated, assuming quasi-static equilibrium. The value of the effective loss coefficient determined over this altitude range is 1 × 10 −7 cm 3 sec −1 at 120 km and 2.2 × 10 −3 sec −1 at 270 km. Above 130 km the calculated total ion density agrees with the measured electron density to within 30 per cent; below this altitude the calculated density diverges, becoming a factor of 2 too low at 120 km. The measured value of the electron temperature is found to be greater than the neutral temperature at all altitudes in the 120–270 km range. This thermal imbalance can be completely explained on the basis of the measured solar EUV heat input at all altitudes above about 140 km. To account for thermal anomalies at lower altitudes, however, it is necessary to postulate an additional heat source capable of raising the electron temperature above the neutral temperature.